2 Insects and Rodents: the Pests of Materials and Products · Insects and Rodents: the Pests of Materials ... the Pests of Materials and Products case of ... reports of caterpillars

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Insects and Rodents: the Pests of Materials and Products

2.1 The Moth as a Pest of Woollen Cloth and Furs

About thirty moth species have been recorded as pests. They damage furs, woollen cloth, as well as stocks of fur and raw wool, felt washers in instruments, leather bindings of books, and clothes [1, 2]. Some moth species inhabit birds’ nests, rodent burrows and carrion and can fly from birds’ nests into houses and storage rooms through ventlights, windows and doors.

The clothes moth is the most dangerous and common pest capable of year-round multiplication and causing large economic damage. The fur moth is reputed to be the second most common pest in countries with a moderate climate. This insect has a worldwide distribution and the variety of species can change in different habitats. The clothes moth is an obligate inhabitant of human accommodation, where, under suitable conditions, it gives rise to between two and seven generations per year depending on the temperature.

The damage from moths is huge: they can be found in many living spaces, dress and fur shops, warehouses, fur, wool and leather processing enterprises.

The moth family (Tineidae) contains a great number of genera and species which are widespread all over the world. It includes small, plain adults, which are well-known pests in houses, causing troubles to people and giving an idea of their appearance. The tinea usually has well developed maxillary palps, while the proboscis can be underdeveloped. The forewings are long and narrow, and the hindwings have a wide villous fringe. The larvae inhabit portable cases [3–5].

Many moth species live in forests, such as on tree trunks, stumps, bracket fungi and in the detritus in birds’ nests. In such places you can see the assembly and even the original mating flight of adult moths such as the cork moth. The cork moth has migrated from its natural forest habitat to human settlements and has become a specific storage pest. In the wild, its caterpillars feed on rotten oak wood and bracket fungi, but in warehouses they damage grain, dried fruit and mushrooms.

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Biodamage and Biodegradation of Polymeric Materials: New Frontiers

This is not an isolated example among moths. About ten species of such pests are known, the grain moth being the most dangerous of these. It was originally a forest species, which develops in rotten wood and timber fungi in nature.

Curious facts: The female Tinea moth lays 50 to 300 eggs per week, and from each of them a small caterpillar hatches. The adult female common clothes moth drops her eggs during flight and many of these land in places that cannot provide food for a future caterpillar. In search of something edible the caterpillar must move, burrowing its way through cardboard, paper or cloth. The females of case-bearing clothes moths and white-tip clothes moths behave differently; they search for a long time to find a suitable place for their eggs. Their caterpillars are sedentary, but despite this fact, they are just as destructive as any other caterpillar.

In heated rooms, the grain moth can give rise to two or three generations per year. Along with stocks of seed grain, food and feed grain, it can damage dried fruit, mushrooms and vegetables, as well as seeds of various agricultural and decorative plants.

Beside plant-eating species, there are many other species of Tinea that consume various animal products, such as hair, fur, wool, feathers, leather, horn, bones, dried meat. They are also able to digest keratin and other tough organic materials.

One of the most dangerous pests for furs, wool and fur skins is the common clothes moth (Tineola furciferella). This small adult moth (with a wingspan 1–1.5 cm) has yellowish or buff coloured front wings and drab hindwings; both wing pairs are glossy, with a visible golden tint. The female lays up to 300 eggs during a fortnight. The development is very rapid: one life cycle lasts from two to four months and four generations are produced annually, so adult moths can be seen flying almost all year round. The caterpillars moult between six and eight times. They spin silken tubes, interweaving food debris and excrement. Pupation occurs at the end of the tube in a loose cocoon. The pupa develops during seven to 18 days. Figure 2.1 shows different moth species [3, 5].

The clothes moth (Tineola biselliella) very much resembles the common clothes moth. It is a bit smaller (the wingspan is 0.9–1.2 cm) and the wing colour is lighter; straw coloured, with a golden gloss. The caterpillars do not spin tubes, but live under curtains woven from food debris and excrement. Fewer eggs are laid (60–100) and the life cycle is longer (9–16 months).

Beside these two species, fur and wool items are frequently damaged by the wool moth (or case-bearing clothes moth, Tineola pellionella), which is similar to the common clothes moth in size, but the wing colour is different; both wings of the front pair have three or four umber spots or patches against a treacle brown background. From May until September, the case-bearing clothes moth caterpillar lives in a portable compressed

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case of silk, which it begins to build immediately after hatching. The moult happens in the case. After the moult, caterpillars build up the old case, and if a caterpillar uses substrates of different colours, the case will show coloured ‘growth rings’. Caterpillars that have finished feeding climb up to ceilings or eaves and rest there until spring after fastening their cases in an upright position. In April, the caterpillars moult for the last time and after leaving the old case, most of them build a new one, where they pupate.

Figure 2.1 Moths. (top left) Case-bearing clothes moth; (top right) common clothes moth; (bottom left) cork moth; (bottom right) grain moth

Moth caterpillars of every age damage the substrate on which they feed. The quantity of materials eaten by the caterpillar during the whole period of development depends on the moth species, the quality of material on which it feeds, and the temperature and relative humidity of the air. Unprotected keratin material can be completely degraded by a caterpillar infestation. The digestive juice secreted by moth caterpillars is alkaline (pH 9.9), and keratin is not resistant to the impact of alkalis. Moths can also cause damage to cloth made from a mixture of natural and synthetic fibres; in fact they have to feed on this more intensively, because the food value of such cloth is lower than of woollen cloth and they cannot digest the synthetic threads [2, 3].

Caterpillars damage materials during feeding but secondary damage is also caused as caterpillars burrow into materials while they search for food and for suitable places in which to pupate, and some caterpillars also use the materials to build protective

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cases. Caterpillars will also damage with their jaws materials such as paper, cardboard, cotton, linen, synthetic fabrics, polyvinyl chloride (PVC) and polyethylene (PE) films, and telephone wire insulation which they cannot use as food sources.

Adult moths do not feed. They fly at nightfall and during the first part of the night, live for seven to ten days, on average, and during this time females lay 60–120 eggs.

Moth caterpillars hide, making different shelters from silk threads. For instance, caterpillars of the case-bearing clothes moth spin a silk tube around themselves, including food debris and excrement in it. This tube is built up as the caterpillar grows and can reach 10 cm in length. Caterpillars of the clothes moth fasten damaged fibres by a silk thread, so that wide curtains will be formed, which cover the caterpillar from above. The carpet moth builds branching channels around and through the material.

Pupation may occur in tight cocoons in the nutritious substrates or far away from the feeding places. For example, caterpillars of the case-bearing clothes moth leave the food substrate before pupation and climb up to ceilings, where they spend the winter hanging in their cases and only pupate in the spring. There have been reports of caterpillars of the large pale clothes moth damaging lime plaster coatings 20–30 mm thick before pupation. The development of the pupa takes one to two weeks. The case-bearing clothes moth and carpet moth carefully choose the place in which to lay their eggs on the food substrate. Adult clothes moths, in turn, frequently drop eggs down on any nutrient and sometimes inedible substrate.

Adult moths fly badly and for short distances only. One has an impression that they are unwilling to leave the place where they have been resting and try to get on to any new resting place as quickly as possible, so are not always easy to see or find. They choose items that are food sources for caterpillars on which to lay their eggs, such as carpets, upholstery, clothes and shoes made from wool and other materials.

Curious facts: Immediately after hatching and having a little snack, caterpillars of the clothes moth and other moth species use a fast-curing silk thread to build an individual tube in which to live. The silk thread stretches from the mouth, which has special spinning glands. From the outside, the silk cocoon is masked skilfully by strands of wool. After building the cocoon, the caterpillar begins to destroy the wool.

The optimal development temperature is 23–25 °C for the caterpillar of the case-bearing clothes moth and clothes moth, 27–28 °C for the large pale clothes moth, and slightly lower for moths resident in bird nests, such as the nest moth and sparrow-nest clothes moths. Caterpillars of these moth species can also survive at temperatures below 0 °C, whereas the case-bearing clothes moth (Tinea pellionella) perishes very quickly.

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2.1.1 Moth Control: Prophylactic Measures

To prevent moth infestation, dwellings or warehouses should be kept tidy and well-ventilated and should be cleaned once a month using a moth killer or repellent. Carpets should be cleaned regularly, and walls and ceilings vacuumed to remove any cocoons that may be present [5]. Natural deterrents, which include substances based on lavender or fir needle essential oils or tobacco, are often used in storage chests for clothes and linens and these give off odours which the adult moths hate. These can only repel the adults but do not kill eggs, and if an adult moth is already present, it is too late to use them.

Curious facts: Naphthalene was first used for moth control as far back as 1887. After a hundred years, the clothes moth became completely resistant to this poison. There are reports that moths even fly towards the smell of naphthalene and caterpillars are no longer affected by it. Another extremely important factor, however, is that naphthalene, which was previously used in households in large amounts, is now known to be carcinogenic in humans. Today, its use is forbidden.

2.1.2 Moth Control: Physical Control Methods

These methods are based on destroying moths by removing by hand, mechanical cleaning, and heat treatment, by ultraviolet (UV) radiation and high frequency currents. At present, the use of infrared radiation for moth control is experimental [5–7].

2.1.2.1 Removal of Adult Moths and Caterpillars by Hand

This is only suitable for use in small areas such as living rooms or small warehouses with low contamination. This method is not very efficient, because the moth is a night creature and any adults that are found may well be females, which have already laid their eggs.

2.1.2.2 Mechanical Cleaning

Eggs and caterpillars that are not firmly attached to fabrics or surfaces can be removed by brushing or tapping. Substrates which are matted together or tangled must be separated by hand and combed out thoroughly. Vacuum cleaning is also an effective method against eggs and caterpillars.

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2.1.2.3 Heat Treatment

Unfavourable temperatures have an adverse effect on moth vital activity and heat treatment is a good and reliable control method. Low positive temperatures decelerate the development of the caterpillars, and negative temperatures kill them. Low temperatures can be used to slow down the development of the eggs or caterpillars. In order to do this, warehouses should be ventilated on frosty clear days and/or cold air can be blown through the shelves where goods or raw materials are stored. Depending on the type of raw material or product which is in the store, ice may be put on to the shelves.

High temperatures destroy both eggs and caterpillars, too. Contaminated goods can be heated to between 60 and 70 °C using sunlight, an oven or by blowing hot air through them.

2.1.2.4 UV Radiation

Sun or UV lamp irradiation treatment is an effective moth control method. UV radiation is absorbed by the insect body and can result in protein coagulation.

2.1.2.5 High-frequency Currents

This is a highly effective moth control method. The disinfecting effect of electromagnetic field currents occurs as a result of very fast (within a few seconds), uniform heating of a treated object. Moth-contaminated raw materials are placed on a special conveyor or between condenser plates. The heating proceeds from the centre to the outer surfaces and disinfection occurs within 8–10 minutes.

2.1.3 Moth Control: Chemical Methods

Insecticides that are used for moth control are classified with respect to their action into internal or intestinal, external or contact, and fumigants which are gaseous (suffocating) insecticides.

Insecticides are used as:

• Solutions, emulsions or suspensions (spraying)

• Dusts (dusting)

• Gases (fumigation)

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• Mists (aerosol treatment)

• Smoke

Insecticides must not be toxic to humans and must not damage goods such as fur, wool, furniture, etc.

2.1.3.1 Internal or Intestinal Poisons

These are applied as dusts or sprays to the nutritive substrate on which the caterpillar feeds, and their effects depend on the amount of poison which is ingested by the caterpillar from this. Intestinal poisons are only active in solution; they destroy the walls of the intestine or generally poison the insect when they penetrate into the blood. Internal poisons include arsenic salts, barium chloride, rare earth metal salts, fatty acids, and siliceous compounds.

Curious facts: Preparations based on synthesised chemical analogues of juvenile insect hormones (allatum hormones) are assumed ideal. It is known that insect metamorphosis (egg – caterpillar – pupa – adult) happens under the influence of a group of hormones, including moulting hormone and juvenile hormone. If synthetic hormones penetrate into the insect organism at the wrong time, they can cause an acute disturbance of the normal development and death. Preparations based on juvenile or moulting hormone are only highly effective in relation to insects and absolutely harmless to people.

2.1.3.2 External or Contact Poisons

In contrast to intestinal poisons, contact poisons affect insects at every stage of their development. Poisoning happens when these are applied to the insect body and is manifested by chemical degradation of integuments, as well as by blocking the airways. These poisons gain access to the inside of the body via breathing and through the outer integument, and then damage the internal organs and nervous system. Poisons of this group are less dangerous for people than internal ones, and examples include caustic soda, potassium hydroxide, anhydrous calcium oxide, and kerosene-lime mixture.

2.1.3.3 Gaseous Poisons or Fumigants

These are highly volatile and are able to penetrate into treated objects and affect insects via their respiratory system and outer integument at any stage of development. As the main fumigants, the following compounds can be used: carbon disulphide,

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paradichlorobenzene, ethyl bromide, sulfur dioxide, and Zitol (permethrin) which is less toxic to humans. Prussic acid and its salts are not currently used.

Curious facts: Is it possible to make wool inedible for moths? Yes, but it is expensive and difficult. We can break the sulfur bridges in keratin by chemical means and replace them by other bonds. Such wool does not change its characteristics and has the same pleasing appearance. There is also a dye, martius yellow, which prevents the caterpillar from feeding. However, this dye is faded and unimpressive, and not many people will wish to wear yellow sweaters, mittens and suits.

The presence of moth infestation of carpets, fur rugs, woollen curtains and so on in the home is indicated by hair shedding, the presence of greyish paths produced by the caterpillar as it feeds, and abundant excrement. The damage to furniture can be seen in the form of damage to the upholstery caused by the feeding caterpillars. If the furniture is upholstered with leather or non-woollen fabric, only the seat cushions stuffed with horse hair will be attacked by moths, and caterpillars, whereas cocoons or webs may be found under the seat on the frame.

Moth infestations found in soft goods such as woollen textiles or fur should be treated as follows: cleaned thoroughly; warmed up, either in the sun or by ironing; and treated with insecticides. It is very difficult to exterminate moths in furniture. The reliable method is to replace hair with a different stuffing material or to impregnate seat cushions which are stuffed with hair with long-lasting insecticides. Heavy infestations in the home can be treated with insecticides by spraying, dusting or fumigation. Staircases, storerooms and attics should be treated as well as living rooms, kitchens and floors.

2.1.4 Guidelines for Storing Woollen and Fur Clothes

2.1.4.1 Woollen Clothes

Before storing, woollen clothes should be inspected carefully and then any contaminated places in which they are to be stored should be cleaned with liquid ammonia, taking care not to inhale ammonia vapours, which can damage health. Clean and well-dried wool clothes should be stored in PE or paper bags. Everything packed for storage should be regularly inspected.

2.1.4.2 Furs

Furs are best stored in dark rooms at a temperature of about –4° C. Such conditions are maintained in warehouses, using special refrigerators for furs.

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At very high temperatures, the leather of the fur shrinks and deteriorates and the fur begins to moult.

Furs should be hung free and, most importantly, must not be stored in sealed plastic covers because fur loses its properties when air is excluded. Furs should be stored in paper or linen covers, in which moth repellents should be placed.

2.2 Leather Beetles – Enemies of Fur and Leather

Leather beetles represent a relatively small but very important group of beetles in relation to biodeterioration. They are dangerous insects which attack plant and animal materials, and cause problems for sericulture and in museum collections. Leather beetles inhabit all geographical areas, except for tundra. The widest variety of species and the greatest numbers are found in dry and hot regions. The main feature of the biology of leather beetles is that they are xerophiles. In nature, they inhabit dried dead animal bodies, nests of birds, burrows of rodents and some preying animals [3, 5].

Leather beetles have an oval or, more rarely, elongated or obrotund body, 1.3–11.0 mm in length and 0.5–5.0 mm wide. They have club-shaped antennae, which may be hidden in a deep cleft in front of the sternum. Leather beetle larvae are mobile, with a rigid cover, are covered by long setae, often with a particularly long seta forming a peculiar ‘tail’. The larva is 1.5–17.0 mm long and 0.5–5.0 wide (Figure 2.2).

The females lay their eggs in small batches in grooves or on the material surface. The duration of the incubation period depends on temperature and may vary from 2 to 55 days. The larvae start to feed soon after hatching and, under optimal conditions, they moult 5–7 times at intervals of 4–9 days. Before pupation the larvae dig into the ground or gnaw a burrow in the substrate, which is 5–10 cm long and ends with a small chamber. The pupal stage lasts for 4–20 days.

The majority of leather beetles have a one-year life cycle but in heated spaces, many species produce between one and four generations annually. They propagate in all places where raw materials and products of animal origin are present. In warehouses, their populations increase very quickly because they have a relatively high breeding power in conjunction with low larval mortality and are highly resistant to unfavourable environmental conditions.

Many species of leather beetles which occur widely in nature attack leather and fur in warehouses and museum collections because these provide the same preferred food sources as are found in their their natural habitats, i.e., hair, feathers, leather and dried insects. The bacon beetle (Dermestes lardarius) which usually consumes dry carrion is

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a typical representative of the family. This black beetle is densely covered with round scale-like hairs and a broad light coloured band crosses the elytra (forewings) and is frequently observed in fur warehouses, where it can damage leather and fur. Its larva tapers towards both ends, has a hairy body and two short curved stiff spines on top of the last abdominal segment.

Figure 2.2 (a) Leather beetle; (b) leather beetle larva

Hair, feathers and antler goods are nutrition sources for the fur beetle (Attagenus pelio). The mature beetle is oblong, and black with two distinctive white marks on the wing cases behind the head. Their larvae are similar to those of the bacon beetle, but without the short curved stiff spines at the end of the body.

The larvae of these beetles live in various different materials and as they feed, they create many burrows and holes in them, and also contaminate the material with excrement, thereby rapidly making the materials useless. In addition, the larvae of many beetle species damage materials and goods which they do not use as a food source but which they use as the substrate for building a pupal chamber. Prior to pupation, the larvae leave the substrates upon which they developed, and gnaw into any neighbouring materials. This is why they damage the walls of buildings in which materials of animal origin are stored and the insides of containers in which they are transported [5].

Most often, leather beetles damage leather and rawhide, fur, feather, wool, meat, cheese, milk powder, dried and smoked fish, glue, museum exhibits and book covers,

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but they can also damage asbestos, cardboard, plastics and telephone cables. At silk farms they seriously damage silkworm cocoons, by gnawing holes in them and make it impossible to unwind the silk from them.

2.2.1 Methods of Leather Beetle Control

Storing foods and some other materials such as fur and textiles at low temperatures protects them completely against damage by leather beetles. The use of very low temperatures for extermination of these pests is only possible in cases when warehouses are infested by species which have come from warmer areas. Leather beetles can be eradicated from goods and materials by heating them to 80 °C for 1–2 hours, so long as the materials are not damaged by the high temperature used.

The volatile repellents which are currently available have a very low deterrent effect on the adult beetles. One of the most effective protective measures is the impregnation of materials with stable substances which have low toxicity for humans. Some of these substances (e.g., tetramethrin and some surface-active substances) have repellent properties; others are strong, or less strong, insecticides. Contact insecticides are used extensively to control leather beetles in warehouses and in homes. Many of them reduce the population of the pests significantly but, in general, do not lead to their total extermination.

The comparative study of many insecticides provides evidence that sometimes, even related species of leather beetles show different responses to the same substances. Therefore, the dosage of insecticide must be calculated based on laboratory trials with the species to be controlled.

Total extermination of any leather beetle species at all stages of development may only be achieved by fumigation of storage areas and materials. Of the currently used fumigants, ethyl bromide is the most effective. For chamber fumigation, dichloroethane, para-dichlorobenzene or carboxide can be used.

2.3 Wood Fretters (Wood Borers): the Enemies of Wood

A healthy growing tree trunk is not usually damaged by insects. The osmotic pressure, which is maintained in the tissues at a defined level by the supply of water through the roots and into the tree trunk keeps them out. As soon as normal transpiration is disturbed and the osmotic pressure in the whole trunk, or part of it, changes the tree will be exposed to insect attack.

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Insects which attack tree trunks have very well-developed mouthparts with two pairs of jaws, which help them to bore easily through the bark and disperse within the tree tissues. After cutting, the tree becomes vulnerable to attack and has a strong characteristic smell, which attracts insects. They find fallen trees very quickly and colonise them. Exposed to insects, the wood quickly loses its properties; the durability decreases, its mechanical properties are reduced significantly, and its water content, bulk and thermal conductivity change. Fungal spores penetrate easily into this wood and it begins to rot. Within a few years, the wood becomes rotten, decays and is reduced to powder when handled. At this point, if such wood is being used as a post or floor board, it will not endure the necessary load [5].

Wood pests can be transferred into houses in the timber which is used for their construction. Most insects which inhabit forest timber cannot adapt to life within a building and will die. However, there are pest species in nature which, over a long period, have become adapted to living in timber which has been used to construct buildings. The wood borer is one such pest [6–11].

Curious facts: Mature wood borers spend the majority of their lives in burrows in the dead wood core, where their larvae are usually developing. Many species produce sounds by tapping the walls of their burrows with their heads. They do it so rhythmically that it has sounds like a clock ticking. Superstitious people call them ‘clock of death’ and believe them to be a bad omen. In fact, these sounds help female and male beetles to find each other in the wood strata. When the ‘clock ticking’ sounds are heard from a wall, table or cupboard, this is a warning for the house owner that his house or furniture is being damaged by dangerous pests – the wood borers.

The common furniture beetle is a member of a small wood boring family, which includes about 200 species; the majority live in warm climates [12, 13]. Historically, there has been a strong connection between the spread of the common furniture beetle and human activity. This beetle is generally found only in buildings because it is transported in infested wood and products made from it, and buildings usually provide suitable conditions in which it can develop. A specific feature of the common furniture beetle is that it attacks wood products, which have been in use for a definite period (5–25 years). This phenomenon is usually associated with the texture and physical state of the wood. The larvae of common furniture beetle can also normally develop on green wood.

The wood borer larvae develop in the inner parts of wood products frequently making them rot, whereas from the outside, only relatively small circular exit holes, through which the beetles leave the wood, are visible. In some species, larva development takes up to three or four years, so even an expert cannot detect infected materials before the first beetle flight. Most often, wood borers appear in old timber, but the adult beetles may fly into a building through open windows.

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Common furniture beetle damage cannot always be evaluated precisely, because wood is often infested not only by the beetle, but also by wood fungi. The wood borer destroys not only the timber in ordinary buildings and wooden items, but also that in unique buildings and items of historical interest, together with museum exhibits, so the loss that they cause is incalculable. It is no wonder that great attention is focused on timber protection. For example, there are special laboratories in restoration workshops dealing with the problem.

When developing, the common furniture beetle passes through four stages: ovum, larva, pupa and adult insect, or beetle, (usually called the imago). The common furniture beetle is 5 mm long, 1.2–1.7 mm wide and is umber in colour. Their antennae are slightly shorter than a half of the body; the last three segments of the antennae are elongated. The living insect has them pointing forwards. The beetle becomes still when touched, and the antennae are hidden in the hollow of the sternum. The head is hidden under the pronotum and is almost invisible from above. The pronotum is hood-shaped with a clear spot in the middle. There are ten rows of equal and distinct dotted striations on the wing cases (Figure 2.3).

Wood borer males are different in appearance from the females. The females are bigger and, moreover, the end of their body is smooth, while males have a pronounced cross hollow on it.

In houses, adult beetles can be observed throughout the year but are most abundant at the beginning of summer. This is time of the so-called ‘flight’, when females and males mate. The term ‘flight’ is not completely appropriate for this pest species, because the common furniture beetle seldom flies and, when it does so, it flies only for a short distance (usually on warm summer days). The majority of beetles stay in the places where they have emerged, or nearby. The reluctance of wood borers to fly explains why they frequently cause localised damage. It is at this stage of their lives that the common furniture beetles produce their characteristic short ‘ticking’ sound, which can easily be heard on summer evenings if there is an infestation in the house.

When disturbed, the beetle draws in its antennae and legs and ‘feigns dead’. This defence reaction helps it to escape from enemies, because when it draws its leg in, it drops and is then difficult to find.

Mating usually occurs in the grooves and cracks which are abundant in dry wood, and only infrequently on the wood surface. Almost immediately after mating, the females begin to lay. About 80 eggs are laid; they are elongated, whitish in colour, 0.5 mm long and 1.2 mm wide. They are observed on wood only with the help of a lens. The eggs are normally glued to the substrate and it is very difficult to detach them from it without damage. The beetles usually die shortly after laying their eggs and the adults have a life span of 6–22 days [5, 12, 13].

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Figure 2.3 (a) Wood borer and (b) its larva

The embryonic development (from fertilisation till larva hatching) lasts for 10–12 days. In this period wood borers are especially sensitive to the impact of external factors, namely to humidity and temperature. At 50% relative humidity the egg survivability decreases, and at 45% they die. Eggs are also sensitive to the impact of high temperature. The eggs are killed by a temperature of 30 °C and the larvae are killed at 45 °C.

The larvae of these beetles are C-shaped, are whitish in colour, have a relatively large head and a covering of slightly reddish short, thin hairs. When the larva hatches, it bites through the end of the egg which is attached to the wood, and penetrates into it. The outlet hole is 0.1–0.2 mm in diameter and is only visible with the help of a lens. As the insect grows, the burrow width increases reaching 2.0–2.3 mm in diameter. The burrows are filled with residual digested wood, which is called wormhole dust. The larvae destroy the interior of the wood but do not affect its exterior, so it is difficult to distinguish infested wood from non-infested wood until after the rounded beetle flight holes have appeared. The feature of many wood borers is that most of burrows are concentrated in the springwood. Therefore, severely damaged wood becomes stratified into separate layers composed of autumn wood. It is of interest that the larvae of some wood borers damage not only wood but are able to live on many plant, or even animal-based, products including opium and dried meat.

The secret of the considerable ability of the wood borer to adapt to different nutritional sources was disclosed by studying their digestion processes. It turned out that beetle larvae have a great variety of intestinal enzymes, which help them to metabolise not

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only sugars, proteins and starch, but also cellulose, the stable component of wood. Moreover, there are special structures in their bodies (mycetomes), containing specific species of symbiotic microorganisms which supply the larvae with nitrogen-containing substances which are available only in low amounts from the wood substrate. The role of symbionts in the life of the wood borer is so great that they are passed on from generation to generation. When the female lays her eggs, the egg surface is covered by these microorganisms. When it bores through the eggshell, the young larva simultaneously ingests a portion of symbionts which then multiply in the mycetomes. Thanks to these allies, wood borer larvae can consume even cellulose. In their natural habitat, however, they prefer old, dry wood which has already been attacked by fungi.

Mature larvae look different from the young ones. They are bigger and, unlike young larvae, have spines on their backs which the larvae press against the walls of their tunnels in order to help them to move along. Before pupation the larva moves to the wood surface leaving an undamaged layer of about 0.5 mm thick. Here the larva converts to a pupa, which becomes an adult insect within 2–3 weeks, and the whole cycle repeats.

The life cycle of the common furniture beetle, from the egg to the adult insect, lasts about a year, at least nine months of which are spent as a larva and it is this stage which causes the most severe damage to wood products and buildings.

Along with humidity, the main factor determining the damage rate of wooden buildings is the probability of eggs being laid in them. If there are few active female wood borers in the vicinity, the likelihood of infestation is lower than if many females are present.

The damage level of wood structures and woodworks depends on how similar the conditions in dwellings are to the optimum conditions for wood borer development. In unheated parts of buildings, such as attics and basements, temperatures which are high enough for the development of wood borers are only reached in summer, except when wood constructions under the leads are wetted due to a defective roof and the relative humidity of the air reaches 60–80%. The conditions in heated areas of buildings are distinctly different. The temperature and humidity must be 21–22 °C and 30–45% respectively in winter, and 13–24 °C and 35–50% respectively in summer.

At any time of year deviations from the temperatures and humidities mentioned above are observed. Nevertheless, temperature conditions in dwellings throughout the year correspond to the optimum for wood borer development. The case is somewhat different for humidity. The usual levels of humidity in dwellings promote quick wood drying. The moisture content of wood adjusts to the air humidity and at normal temperature the absolute moisture content of wood is 11–17%. Therefore, the air humidity in living quarters is quite unfavourable for wood borer egg development, and the moisture content of wood is lower, than that required by the larvae. Common

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furniture beetle clusters are concentrated in places where, for any reason, the air humidity and moisture content of wood is increased.

The floorboards of ground floors, basements and kitchens, and the ends of wooden beams become wet most frequently. In wooden houses the wood borer is frequently found in lower timber sets of walls, beams and the floor boards of ground floors. This pest is also detected in base mouldings, especially at the external walls, and the bottom part of the door frame. Inspections show that the greatest damage occurs in floors, followed by timber frames, doors and door frames. Partitions are damaged less frequently because they dry relatively quickly [5, 12, 13].

The appearance of common furniture fretters indicates either defects in the construction of the building or inadequate ventilation or use of the building which increases the humidity of the air and the structure as compared with normal levels.

The tunnels made by wood borer larvae and flight holes made by the adults are called ‘wormholes’ and can be detected on growing trees, stored wood and in furniture, parquet flooring, plywood, timber or chipboard. The wormholes appear as grooves and oval holes of different depths and sizes. They can be described as ‘surface’ (up to 3 mm below the wood surface), shallow (5–15 mm below the surface in round timbers) or deep (more than 15 mm below the surface). They may be small (not more than 3 mm in diameter) or large (more than 3 mm in diameter). These tunnels destroy the outward appearance of the wood and the commercial value of the wood. A large quantity of wormholes reduces the mechanical properties of the wood, but only surface wormholes do this. The presence of wormholes means that the affected wood cannot be used and is therefore wasted [14–17]. If living beetles are found on the premises, the infested places in the timber or furniture must be found and only then should measures against wood borers be undertaken. The focus of the damage is usually determined by the presence of flight holes in the wood. However, it should be determined whether or not this damage focus is active (i.e., if there are larvae in the wood), or if all the adult beetles have flown away. The presence of tunnels in the wood indicates that at least some of the adult beetles have flown and this is the main difficulty. Common instructions on furniture beetle control recommend looking for wormhole dust which can be seen outside the tunnels. This is believed to be a reliable sign that larvae are present in the wood. In most situations, inspection is the only method used, which takes account of the presence of flight holes, the hole edge contamination rate (new holes which have clean edges and fresh wood is visible) and the presence of wormhole dust pouring out from the burrows. It is necessary to search thoroughly for infestations which are hidden from view in crevices etc. However, the X-ray method is more reliable, because it clearly shows images of larvae on the film and this confirms that the source of the damage has been found. The X-ray method is normally used in museums to evaluate the degree of wood infestation.

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In houses, common furniture beetle (Anobium punctatum) is also frequently observed. It is dark-brown, with 3–4 mm long cylindrical body, covered by a thin grey indumentum. Its larvae damage furniture, frames, floor, ceiling beams and wall beams. The common borer (Anobium pertinax) is slightly bigger and has two light spots in front angles of the pronotum. Its larvae usually appear on attic floors, in the corners of rooms and on floor boards, but they do not damage furniture.

The larvae of the drugstore beetle (Stegobium paniceum) are omnivorous and will feed on crackers, stale bread, furniture, dry insects, book covers and many other materials. In libraries, it is called the ‘book beetle’; in food warehouses, it is responsible for ‘wormy’ crackers and in museums, its larvae damage stuffed animals. The beetle itself is 2–3 mm long and brown in colour. It inhabits dwellings, and in the evening it flies toward light.

2.3.1 Control Measures Against the Common Furniture Beetle

All control measures are divided into three groups: those that are used for buildings and households, and those that are chemical and physicomechanical. [5, 6, 7].

Prophylactic measures prevent wood borer damage of wooden structures, wood products or furniture for a long time. Some are for buildings and households and some are chemical methods. These measures should be effective for as long as possible, because in most cases they are carried out only during construction and repair; using them in completed buildings is very expensive and is difficult to do.

Destructive measures are used for the extermination of wood borers which are already living in wood. Some are physicomechanical and others are chemical methods. Destructive measures completely exterminate wood borers, but only for a relatively short time. With respect to this classification, the requirements to different control measures also change.

Constructive measures for wood protection against fretters include the entire group of measures which are applied to the wood where the trees are felled, in warehouses and when it is used in the construction of buildings. They include cutting practice, the length of time taken to remove it from the cutting area, the storage regime and the regulations which apply to wood use. The main goal of constructive control measures is to limit the possibility of the wood borers getting into the wood in the first place or to stop their further development if this does happen. In a completed building, wood borers appear either during the summer or are brought into it in infested wood.

To eliminate an infestation, the affected wood must not be stored, but burned immediately. Old furniture should only be brought into dwellings after it has been

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inspected for infestation by the common furniture beetle. Of course, even if these measures are carried out thoroughly, it is still possible that the wood borer may appear and, if the conditions are favourable, it will lay its eggs and the resulting larvae will damage the wood. Therefore, the second stage of control measures includes the creation of conditions, under which eggs and larvae cannot develop.

Chemical control measures include the use of different poisons (insecticides) for fretter extermination. Insecticides are divided into three groups according to the way in which they affect the fretters: intestinal, contact insecticides and fumigants (preparations which affect the respiratory system). Intestinal insecticides affect wood borers, when they entered the intestine and are ingested from the food substrate, contact insecticides have an effect after physical contact with the beetle body surface and fumigants poison the beetles after inhalation.

The main part of the life cycle of the wood borer (8–10 months) is spent as a larva and pupa inside the wood and the adult insect lives for only two to three weeks after leaving the wood. This way of life significantly complicates the control of these insects and puts additional demands on the pest killing agents.

Insecticides applied against fretters must be highly toxic for insects and must remain active for a long time when injected into wood. They must have a low toxicity to humans, must not reduce the physicomechanical properties of wood and should have an objectionable odour in order to repel the insects.

For the control of wood borer larvae, the wood is treated with chemical agents, including benzene hexachloride, turpentine mixed with kerosene, wax, paraffin and kresosolvin or a mixture of turpentine, kerosene and phenol. These methods do not, however, ensure reliable and long-term protection of wood against insects. Larvae are only completely exterminated after high-frequency current treatment of the infested wood.

2.4 Cockroaches

Cockroaches are an ancient group of insects: typical representatives of this order have been found in sediments from as early as the Middle Carboniferous Period. At that time, they apparently formed a large part of the insect population. It is understood that before the Tertiary Period, there were no wingless forms or forms with shortened wings among the Dictyoptera order species.

Dictyoptera have a flat oval body and a head with turned down mouth and which is nearly, or completely, covered by a large shield-shaped pronotum. Their antennae are multiarticulate, setaceous; the pedicels are rudimentary with flattened hips and

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five-jointed tarsus. The elytrum and wings can be shortened or absent. The abdomen is extended and consists of 8–10 segments with soft vestitures. The majority of Dictyoptera have a light russet coloured body and elytrum, but less frequently these may be dark or black in colour. The flattened body and dense exterior vestiture of the cockroach are perfectly suited to lifestyle of this insect. Most cockroaches are nocturnal but some are not. Cockroaches with different lifestyles have different external appearances.

Many cockroach species, including the German cockroach and the oriental cockroach are known as synanthropic species (i.e, they are ecologically associated with humans). The German cockroach (Blatella germanica) is brownish-red in colour with two dark strips on the pronotum and is 10–13 mm in length. It was originally imported into Europe from southern Asia and propagated very quickly. Blatella germanica inhabits warm, heated rooms, especially kitchens, where it feeds on various products of animal or vegetable origin. It is thermophilic and hates low temperatures. At 22 °C, it becomes mature after 172 days, but at higher temperatures of about 30 °C, the development stage decreases to 75 days. However, these cockroaches die within 30 min at temperatures below –5 °C and within one minute at –7 °C.

The oriental cockroach (Blatella orientalis) is a bigger species (18–30 mm long), with a black or blackish-brown shiny body. The elytra of the male are slightly shorter than the abdomen, and females have them short, shaped as small squamous blades (Figure 2.4). This insect produces a secretion with an offensive smell from special cutaneous glands [4].

Figure 2.4 Oriental cockroaches. (a) Male; (b) female; (c) female with an ootheca

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The origins of the oriental cockroach are not known but it appeared in Europe, at least, 300 years ago. It is usually found in buildings in the same places as the German cockroach, consumes the same food sources, and both are nocturnal. The larvae grow very slowly and take up to four years to reach maturity.

The chitinous cuticle of cockroaches consists of three layers and a layer of wax protects them from dehydration and drying. The ability of these insects to tolerate extreme climatic conditions, their sensitive tactile organs and their quick responses help them to survive. Even the soft footsteps of a person are perceived by the nervous system of the cockroach as an earthquake, and an air blast from a thrown slipper warns that danger is near, and the cockroach disappears immediately. This sensitivity is granted them by two tactile organs: filiform and corymbiform. Filiform organs have an extremely thin hair fixed on the chitinous vestiture by a flexible membrane. At the base of the hair a tactile cell is located, which is even excited by a very low displacement from the state of rest. Corymbiform organs are of similar structure. Excitation is transmitted through them to the nervous system. They are bound to structures resembling ear drum membranes for perception of hardly perceptible vibrations. These tactile cells are located at the back end of the insect body. Sensitive cells in the tarsus register even insignificant vibrations. The phenomenally swift reaction of the insects to vibrations is provided by the nervous system which is spread throughout the entire body of the cockroach from the tip of the abdomen to the brain. The danger signal is transmitted from the tip of the abdomen to the brain as quickly as 25 m/s. When the nervous impulse from the distal end of the body passes through the thoracic zone of the cockroach, where the thoracic ganglia are situated, the signal is transmitted directly to nerves which control the muscles. The danger signal causes an instant response of the insect to flee, even before it reaches the brain.

Cockroaches have valves in the spiracles which close if the insect detects any toxic materials in the air. This mechanism provides them with high resistance to poisons applied as powders or sprays.

The mandibles of the cockroach form sturdy jaws which bite off pieces of food and these are then manipulated into the mouth by other mouthparts (the maxillae and labium). The labium and maxillae are also used to clean the antennae. The entire foregut of the cockroach is lined with chitin which, in the gizzard, forms proventricular teeth and a plate which are used to grind the food.

Cockroaches live in groups that have no leaders; unlike ant colonies, there is no social hierarchy in these groups but they have ‘scouts’. A scout is a young, strong and quick individual that can travel far away from the colony and usually knows exactly where food and further shelter may be located, and where danger may occur.

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If they have gorged themselves, some species of cockroach may be able to then go without food for between 40 and 80 days, and they can also survive for several days without water. The female cockroach lays batches of eggs every 4–6 weeks. The immature stage of the German cockroach lasts for between five and 180 days, and for oriental cockroaches it can be extended to four years.

The egg laying process is quite unusual. The eggs are released from the oviduct, one by one, and accumulate in the egg chamber, where they adhere to one another by means of a specific secretion and a capsule, the ootheca is formed. The ootheca usually contains from 15 to 40 eggs laid in symmetrical coupled rows. It is usually oblong in shape, is slightly compressed from the sides and there is a row of kinks on the upper edge. The case of the ootheca is resistant to many chemicals, including alcohols and acids.

German cockroach females can lay three or four oothecae duirng their lifetime. They carry their egg cases on the end of their abdomen until just before they hatch. Some species hide their oothecae in safe, protected places.

However, not all Dictyoptera form normal oothecae at egg laying. Approximately one third of species produce immature capsules, which represent thin membranes and are destroyed during laying of eggs. In these cases, eggs are laid in small packs without any protective cover.

The embryos develop inside the eggs for 20–50 days, depending on the temperature and air humidity. When they hatch, the juveniles (nymphs) do not resemble mature insects. They are small, different in colour, they have no wings and the antennae contain fewer segments. For example, the mature German cockroach has about 85 segments in its antennae, whereas those of a newly-hatched nymph have 19–24 segments.

In the course of its development, the cockroach nymph moults between five and nine times. Different species have a different development cycle and life duration, which depends significantly on the temperature. At 22 °C the German cockroach takes six months to reach maturity and therefore produces two generations per year; at 30 °C, however, the development period is only 75 days.

Cockroaches are able to reproduce rapidly under favourable conditions and a proportion of the eggs and nymphs will always survive. Cockroaches can develop resistance to a new poison within, at most, six generations (i.e., in about one year). This means that pesticides must be changed every year in order to prevent the insects from becoming resistant to them.

The extraordinary ability of cockroaches to survive is easily explained because they are almost omnivorous. They prefer plant-based food sources and they like beer

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very much. They eat bread, potatoes, grain, vegetables, sugar, leather, cotton wool, wool, shoe cream and even books. Cellulose-degrading bacteria in the cockroach’s gut enable it to feed on paper and cellulose fibres.

Cockroaches colonise areas behind heating radiators, in drawers, gaps between the floor and mouldings, behind crumbling plaster, loose tiles and wallpaper, in heaps of paper, newspapers and magazines, and inside any closed and permanently operating equipment. Zhuzhikov and co-workers have investigated the problem of failure of computers and audio and video equipment caused by cockroaches. They have found that computers provide an ideal habitat for cockroaches because they are warm and dark inside [4]. The mature insect, 5–6 days after its final larval moult, may begin to eating synthetic materials such as, PE and PVC insulation of wires. As a result, short circuiting may happen.

Cockroaches are dangerous for man, not only because they damage foodstuffs and other materials and contaminate them by their metabolites, but also because they can spread various bacteria and helminth eggs. They carry bacteria which cause dysentery and other human gastrointestinal diseases both on sensory hairs on the legs and inside their intestines, and these pathogens are then expelled in the cockroach excrement. Whipworm and seat worm (threadworm) eggs have been found in the intestine of the oriental cockroach, and in the German cockroach intestine, along with these mentioned above, broad fish tapeworm eggs were also detected.

Curious facts: Studies on asthmatic children have indicated that the most frequent cause of the disease is cockroaches living in bathrooms and kitchens and that the allergy is caused by cockroach excreta and dead insects. The dust mite reproduces in the chitinous cuticle of dead cockroaches, and this is what causes the allergic reaction. The number of allergy cases in children caused by cockroaches is comparable only to the number of cases of allergic asthma caused by dust. Only 3% of asthma are sensitive to pets, whereas 37% are allergic to cockroaches.

2.4.1 Chemical Methods of Controlling Cockroaches

Insecticides to control cockroaches may be administered in various forms including sticks, gels, powders, aerosol cans, traps and bait. Four main classes of insecticides are used to control cockroaches [7, 14, 15].

The first, most well-known, class of insecticides is the organophosphorus compounds (FOS), which are highly toxic to both cockroaches and man. It includes the following compounds: karbofos (malathion), sulfidofos (fenthion), dichlofos, methylacethion.

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The second class is carbamates. The mechanism of action of this class of compounds is very similar to that of FOS; however, they are more toxic and, consequently, more dangerous for people. Of this class, only propoxur is used in some aerosols.

The third class of substances, and the least harmful for man, is the pyrethroids. These are various synthetic compounds based on of pyrethrum powder. Pyrethroids have a strong neuroparalytic effect on insects, but are relatively harmless to man. Pyrethroids retain their insecticidal properties for 2–6 months, whereas FOS provide protection for only 2–4 weeks. The most commonly used pyrethroids include permethrin, cypermethrin and deltamethrin.

The fourth class of cockroach control methods includes biological preparations, which are specially selected microorganisms that will attack cockroaches. This group also includes hormones which are able to disrupt the normal development of the insect.

Curious facts: On the rapid transit railway between Tokyo and Osaka, war was declared on cockroaches, which had colonised the train cars. For this purpose, new strong insecticides were used. This had to be done, because the six-legged freeloaders were not only damaging the image of the superhigh-speed express, but could potentially endanger the lives of passengers. If they get into control panels they can cause an accident; on one occasion a cockroach got into a fuse box and caused the power to fail. Even electricity was suggested as a weapon against the cockroaches; two naked copper wires were placed under the mouldings, where the cockroaches liked to be and when they crept into the gap between the two wires, they caused a short circuit and were electrocuted.

Encapsulated insecticides remain active against cockroaches for a long period. FOS group compounds are often administered in this form. The active substance is sealed in microcapsules which are placed in water and then sprayed on to the areas where the cockroaches are living. The capsules become attached to the cockroach antennae, their outer coat deteriorates and the insecticide is released. These poisoned cockroaches bring these capsules back to their nests and poison the entire population. This method is odourless and, therefore, can be used by persons with any type of allergy. If cockroaches have become resistant to these preparations, bait can be tried. Most of these contain a substance extracted from insect pheromones, which attracts the cockroach. Some baits, such as Tanglefoot, are adhesives which physically trap the cockroach until it dies. These usually take the form of cardboard boxes with the adhesive on the bottom. Other baited traps contain poisons which the insect consumes and then dies. For maximum effectiveness, it is necessary to use many containers of bait; the Tanglefoots should distributed at a density of one per 5–10 m2, and baited traps containing poison at a density of one per 1–2 m2.

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2.5 Termites as Tropical Pests

Termites are often called ‘white ants’ because their social hierarchy resembles that of ants. They frequently build cone-shaped structures and, similar to ants, most of the termites in a colony are not able to reproduce. However, termites are only distantly related to ants. Termites are virtually unknown in temperate climate regions; their main environment is the tropics and subtropics, especially the tropics.

These social insects with pronounced polymorphism are organised into a number of castes. Their body is oblong and oviform, slightly flattened from above. The head and thorax occupy nearly half the body and the pronotum is small. These insects rely on their legs in order to move around. All six legs are of the same size and the tarsus of each consists of four parts. Only the fertile males and females in the colony bear membranous wings with a vestige of rib network, and these fall away after mating. The compound eyes of the reproductive forms of termites are usually protruded and located on either side of the head and, in addition, the majority of species have a simple eye next to each compound eye. The mouth, especially the upper lip, is well developed; the upper lip ends with a cogged jaw; moreover, the lower jaw and the lower lip, including four lobes, are present (Figure 2.5) [5].

The termite varies from brown to pale in colour. The difference between the sexes is strongly pronounced. The larvae are very small with a thick covering of hairs. Transformation into an adult insect happens by multiple moulting.

Despite a great difference from Dictyoptera in their way of life, appearance and features, termites are closely related to them, but they converted to living underground and acquired the ability to live in large colonies in which the tasks are shared by individuals.

Figure 2.5 Termites. 1 Female (‘queen’); 2 male (‘king’); 3 big ‘soldier’; 4 small ‘soldier’; 5 big ‘worker’; 6 small ‘worker’; 7 nasute ‘soldier’

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Curious facts: Brehm [16] told a fascinating tale about an Arab who fell asleep near a termite nest and woke up absolutely naked: the termites ate all his clothes. The famous traveller Humboldt wrote that it was almost impossible to find a book in South America that is older than fifty years because everything was destroyed by termites. Termites destroy whole settlements, forcing people to move elsewhere. In India the annual damage from termites is estimated at 280 million rupees. In 1875, termites brought to the island of St Helena totally destroyed Jamestown. Termites are present in Hamburg and Paris, have occupied nearly the whole of Italy and have not spared even the Papal Library in the Vatican or the famous Doges Palace or St Mark’s Cathedral in Venice. They are also destroying one of the most famous Italian landmarks, the thirteenth-century cathedral in Siena, and the National Library.

The complex social organisation of termites is based on a strict caste system, in which every group of insects plays a specific role. The colony may contain several hundreds, or hundreds of thousands and even millions, of individuals. In each colony, there is one egg-laying female (the ‘queen’), and one fertilising male (the ‘king’). They are sexually mature individuals whose wings were shed after mating. The sole purpose of the pampered king and queen is to spend their entire lives producing eggs in order to maintain the colony. If they die, they are replaced. Several newly emerged males and females may be observed in colonies at particular times (before swarming). In appropriate weather conditions and at a designated time, these individuals leave the nest to establish new colonies.

‘Workers’ are responsible for every activity related to foraging, food storage and brood and nest maintenance. They also take care of ‘soldiers’ and the king and queen, which are not able to feed themselves. The majority of the termite nest population consists of workers. Workers are sexually undeveloped males and females, which is different from ants, whose workers are always females. The integument of the workers is soft, thin and is white or grey in colour. The workers of fungus-cultivating termites even have even transparent head capsules, and the internal organs of the insect are visible through the integument. This is because they live permanently inside the nest, in the humid atmosphere. The eyes of the workers are underdeveloped or frequently absent.

Soldiers are specialised workers and are characterised by a well-developed head capsule and strong, long jaws. These jaws are used to defend against enemies, i.e., termites of other species and, above all, against ants. Some ‘nasute’ soldiers have a gland canal in the head apophysis, through which a paralysing liquid is sprayed on enemies.

When a new colony is formed, the king and queen feed the first larvae themselves and when these first larvae grow older, these become workers and take over the role of providing food, feeding the queen, king and larvae and nest maintenance. Other larvae then become soldiers. At first, only workers develop from eggs, then soldiers, and only in large nests do winged individuals appear.

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As the colony grows, the queen changes noticeably. Its wing-bearing muscles, limb muscles and even oral pharynx atrophy, i.e., devolution takes place. The abdomen becomes swollen, due to the accumulation of eggs. The queen becomes motionless and depends completely on the workers for food. She lays eggs continuously and workers care for the larvae, which become new workers. The termite queen secretes substances which are licked off by the workers. These substances contain telergones (pheromones), which inhibit the sexual development of the workers. New kings and queens are formed only when the colony has increased in size and the queen becomes weak. The rate at which the queen termite lays her eggs is remarkable. A Microtermes arboreus female has laid 1,680 eggs a day, and a Nasutitermes surinamensis female has laid 3000 eggs in 28 hours. The female lives for many years, during which time she will have laid millions of eggs. If the female dies, replacement females begin to develop in the nest. These substitutes do not fly, but start to reproduce.

Curious facts: In the nests of many omnivorous termites some microfungi (generally mould fungi) are cultivated and are grown on specially laid accumulations of excrement and pieces of wood. Some of the fungi cultivated in termite nests are not found either in the surrounding soil or in the bodies of the termites. These fungi are generally used for feeding young larvae. Cultivating fungi in termite nests provides not only a food source, but the fungi also help to maintain an optimum environment by emitting heat and absorbing moisture which, in drought conditions, may be released into the air.

Termites generally eat vegetable matter. Only the workers are able to feed themselves. Soldiers do not feed themselves because of the excessive size of their jaws and unsuitability of their other mouthparts; workers feed them either by secretions from the mouth or from the anal orifice. After the colony has become established, kings are fed by excretions from salivary glands of workers or larvae. The youngest larvae are also fed by workers, by excretions from salivary glands or chewed fungi spores. The main food consumed by termites in tropical forests is plant and animal residues, the humus, decomposing in soil. The workers eat various residues in the soil, such as rotting wood, foliage, dung or animal skin, but not all the food is digested immediately. Back in the colony, the excrement of the humus-eating termites is then eaten by another worker or a soldier. Thus, the same food passes through a number of individuals within the colony.

Many termites consume wood, sometimes dry wood and even pure cellulose. Termites are unable to produce their own cellulase enzymes. Cellulose digestion by termites is performed with the help of flagellates which are permanently present in the intestine and are able to degrade cellulose. Termites use their digestive symbionts (flagellates) as a source of proteins. It is of interest that termites have the same flagellates in the intestine as wood-destroying cockroaches and this can be seen as biological

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evidence of the idea that termites and cockroaches are related, which can also be seen by tracing the similarities in many of the other organisational characteristics of these orders of insects. Additional protein sources for termites are symbiotic bacteria which are able to fix nitrogen and synthesise proteins and these are also found in these insects.

For a long time it was assumed that the flagellates inhabiting the termite intestine helped them to process cellulose. However, it became clear later that the flagellates themselves need the help of endosymbionts living in their own cells, which produce cellulase (the enzyme that decomposes cellulose).

Thus, this symbiotic system is constructed on the ‘nested doll’ principle: flagellates live in the termite intestine and bacteria live in the flagellates. Termites find food (plant residues or wood-containing materials) and grind the wood pulp finely, so that flagellates can consume it. The bacteria living inside the flagellates then start working to carry out the main chemical changes which transform the originally inedible products into a digestible form.

However, many aspects of this system were unclear. For example, the nitrogen content of termites is considerably higher than that of plant tissues and it was not known how termites obtained all their necessary nitrogen. Recent research by Japanese scientists has answered this question. Hongoh and colleagues studied a symbiotic system of the termite Coptotermes formosanus which is a very big pest in Japan. This underground species causes great damage to wooden structures, not only in south east Asia, but also in America, where it appeared accidentally. Some hundred million dollars are spent annually on control measures against Coptotermes formosanus in Japan, and about a billion dollars in the United States.

Pseudotrichonympha grassi is the flagellate living in the hind gut of the termite, and members of this genus are frequently found in different underground termites. About 100,000 bacteria live in every flagellate and the bacterium which lives in Pseudotrichonympha grassi is known as phylotype CfPt1–2.

In this study, the cell membranes of flagellates excreted from the termite intestine were destroyed and 103–104 cells of the endosymbiotic bacteria were obtained. The obtained bacteria volume was subject to amplification (the increase of the number of copies of deoxyribonucleic acid (DNA) molecules), and then a particular sequence of genes was searched for. The sequence of genes which was discovered enabled the entire metabolic system of the endosymbiotic bacterium to be reconstructed. The most striking finding was the discovery of genes responsible for the synthesis of enzymes which are necessary for nitrogen fixation (the process of capturing atmospheric nitrogen and transforming it into a form suitable for consumption by the organism).

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In particular, genes for the synthesis of nitrogenase were found, a most important enzyme that decomposes a strong double bond in the nitrogen molecule. Genes which code other proteins necessary for nitrogen fixation were also found.

The authors of this work note that the termite ability to fix nitrogen had already been observed, but it was unclear which symbiotic organisms were responsible for it. The discovery of genes responsible for nitrogen fixation in the examined endosymbiotic bacteria was surprising, because nitrogen fixation by bacteria of this group (Bacteriodales) had never been reported before. Along with nitrogen fixation and conversion of nitrogen into ammonia, these bacteria are apparently able to utilise nitrogenous metabolites, which are generated in the course of protozoa metabolism. This is of importance, because nitrogen fixation consumes a large amount of energy, and if there is sufficient nitrogen in the food of termites, the intensity of nitrogen fixation can be reduced.

The newly hatched termite does not have these symbionts (flagellates and bacteria), but acquires them from the older workers which feed it. The flagellates and bacteria which now live in the termite intestine are apparently direct descendants of the organisms which lived in termites millions years ago. As a rule, in spite of the place of habitation, termites of the same species possess a specific set of flagellates and bacteria. The vital importance of symbionts for some termite species was proved by exposing the insects to high temperatures or pressurised oxygen. Neither procedure harmed the termite, but its gut organisms were killed and after these treatments, the termites without endosymbionts starved to death [3, 5].

Different species of termites build their nests differently. For example, in hot countries that have a monsoon climate, with alternate wet and dry periods, termites sometimes build very big constructions (termitaria). These big structures are made of strongly cemented clay, sometimes so hard that even a crowbar cannot damage them! The terminarium is the roof above the underground part of the nest; there are chambers inside these constructions which contain the larvae and ‘fungi gardens’. All termites (larvae, workers and, of course, the egg-laying queen) are very sensitive to moisture deficiency in the air, but are also sensitive to condensed moisture. That is why they build these structures with waterproof walls and inside these, a specific microclimate is created. In open areas, termitaria are often oriented and constructed so as not to be overheated by the broiling sun. Termite nests may have a narrow oblong form and may be positioned so that the axis passes in approximately a north-south direction. Sometimes they can be conical to provide water runoff from the walls; in other cases, they have an overhanging, umbrella-shaped roof. Termite nests are frequently not very high but can be so big that, in India for example, large animals such as buffalo and even elephants seek shelter in destroyed termite nests.

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The nest interior can be organised differently, depending on the termite species. As a rule, the ‘royal chamber’, where queen and king spend their lives among the workers, is in the centre. Galleries with passages connecting them lead from this ‘throne hall’. The thick external walls of the nest are frequently pierced with small holes, which apparently serve for ventilation purposes. Many termite nests have gutters, which like an inclined house roof let water trickle down quickly, and overhanging covers, so that rain flows down without getting inside the nest. Some termites, especially Southern and Central American ones, build ‘cardboard’ nests as big as a barrel on the trees, and construct channels along the trunk to drain water from the nest. All these constructions, different in form and size, are made of only a few simple building materials. Some termite species cement lumps of soil with saliva, some bind soil with a liquid excreted from the intestine, and others combine fresh and half-digested wood with soil pieces. Using different forms of behaviour and engineering techniques, termites ventilate the nest to regulate the humidity and temperature inside it.

Curious facts: Termites consume wood from the surface, and cover destroyed parts by a hard clay crust, the so-called ‘modelling’. If modelling is noticed, appropriate measures should be undertaken to eradicate the termites. A varnished, shiny new piano was torn to pieces by termites: a worker termite carved its way through the wooden floor straight into the piano leg. Having tasted ‘delicious wood’, it informed its fellow workers and a secret, noiseless feast began until all that remained of the piano body was its thin varnish coating.

All wood buildings are vulnerable to the destructive activity of termites. A wooden house only stands for a few years but even stony foundations do not protect wooden structures against termites. These water-loving and photophobic insects build covered arcades on the surface of the stony parts, gluing them together from clay-like pieces so that they have contact with the soil. The inner surfaces of these passages are sprinkled by excreted liquid to keep the necessary humidity in the galleries. Using these galleries, termites can reach wooden ceilings and literally pierce them with holes. As a result, ceilings fall, and floors collapse. In a house that has been left empty for a few months the furniture may crumble at a slight touch. Termites gnaw out tunnels in the wood so that only a thin layer remains on the surface to shield the termites from the open air. The wood becomes very light in weight because its interior becomes hollowed out as the termites destroy it to form galleries.

Different termite species, for example soil and wood termites, can damage different materials and items. Since wood termites only gnaw chambers and passages in wood and remain inside it as a rule, their worker castes can only be transferred into a building or other structures inside infested wood. The presence of splits and cracks in the wood will aid termite penetration. They can also tuck into and inhabit fibreboard and chipboard, plywood, cardboard and other materials containing

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cellulose. Damage to inorganic materials by wood termites is only possible via direct contact with the infested wood.

Soil termites forage outside their nests and can travel for considerable distances in search of food. Meanwhile, they are able to feed on many materials, even inorganic ones, on their way. Building modelled galleries, soil termites bring the soil into different cavities and can contaminate many materials and structures. These termites usually have the largest populations and will become distributed throughout an entire building, forming numerous colonies, due to which their damage rate considerably increases.

As shown in biological tests, termites are able to damage any fabrics from natural, artificial, and synthetic fabrics to glass fibres. However, the degree of damage to different fabrics differs. Resistance to termite damage depends on the same characteristics, which determine the strength of fabrics by cutting with scissors or die tooling: thread twisting, type of weaving, density and thickness of cloth. The most resistant ones are very thick and fleecy fabrics.

Termites usually damage polymer films along the edges or in folds. They are also able to damage fabrics with plastic or latex coating, laminate film materials reinforced by textiles, by attacking the edges, using rhythmic jaw motions and tearing nipped off pieces with the head or body motion. Such materials are usually damaged more slowly than flat fabrics or films, but none of them are completely resistant to termite damage.

As the majority of termites feed on wood, they can damage the wooden parts of buildings. The resistance of different wood species to termites depends on their hardness and width of growth rings. Some species which have especially hard wood are rather less badly damaged by termites.

Curious facts: Termites do not attack people directly, though all travellers rank them among the horrors of tropical countries because they are able to destroy property in a short time. They destroy objects with their jaws, such as clothes, books and household items, wood, bone, leather, paper and various foods; they gnaw out house walls so that the walls collapse and can injure people. In some countries, in order to protect against termites, some people hang up things they want to protect on strings from the roof of the house, or goods may be laid on a table, the legs of which are standing in water.

Some wood termite species penetrate into the open surface of the wood, but these usually inhabit regions with an extremely damp climate, where the humidity of the wood cell walls is close to saturation. Other termites only damage wet wood, which is in contact with the soil, or cover it first with clay modelling, under the shelter of which a cavity with higher humidity is formed. In the presence of termites, the humidity in passages and chambers inside the wood is kept close to saturation.

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The results of laboratory and full-scale tests of filled and non-filled polymer moulded materials show that termites are only able to damage a few of them. Those which can be damaged are some thermoplastics, primarily high density PE and plasticised PVC. However, even some types of these are resistant to termite damage.

Special tests indicate that all phytogenic materials without special protection are subject to ‘edible’ termite damage. In Russia, no termite-resistant wood species were found. Paper is completely destroyed by termites; cardboard is also severely damaged and consumed by them. All kinds of cotton and linen cloths, including ones manufactured in the so-called ‘tropical version’, are severely damaged. Materials of animal origin attract termites to a lesser extent, but they are damaged quite intensively and, possibly, used as a supplementary food source.

A common stimulus for termites to damage ‘inedible’ materials is if they form obstacles on the way to food, water and nest. However, the presence of natural food for termites close to ‘inedible’ materials is of high importance. Constructions which contain no ‘food’ materials attractive for termites are undoubtedly less susceptible, but if they do contain food materials, termites can simultaneously quite severely destroy an ‘inedible’ material and contaminate the entire structure with soil and excrement. Synthetic and mineral cloths from glass and asbestos fibres, particularly with varnish, latex and rubber coatings, are easily damaged by termites which can gnaw through PE and PVC films, Teflon (polytetrafluoroethylene) and polyesters, and they can create substantial cavities in foamed plastics. Hard, nonporous materials with a smooth surface cannot be used by termites and the fact that such polymers are usually highly resistant to them depends on the physical and mechanical properties of these materials.

One of the main termite control measures is the use of redwood beams in house building. A large content of tannin makes redwood inedible, or even toxic, for termites.

The physiological specificity of termites and, primarily, their requirement for high humidity govern the degree of damage which is likely to occur for different materials. Items or buildings containing materials such as wood and other materials attractive for termites can be classified according to their susceptibility to termite attacks and the control measures employed. The kinds of items and buildings are as follows [5]:

• Fully isolated items. This type includes items, in which nutritive material (for termites) is securely isolated from possible contact with termites. They are hermetically sealed items, such as cables, etc.

• Items isolated from the soil. This group includes wood components of modern stone buildings, furniture and other items located in premises, to which termites cannot gain access from the soil. These constructions can only be damaged by dry wood termites, which do not live in Russia.

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• Mobile items. These include railway carriages, trucks and especially all-purpose containers, which transport goods all over the world. Quarantine regulations impose special requirements on them regarding the possibility of bringing in pests such as termites in their wooden parts. International standards require that the wooden parts of such containers must be impregnated with arsenical preparations which are highly toxic for termites.

• Items in contact with the soil and away from human habitation. The wood of railway sleepers, poles, bridges and hydrotechnical structures must be protected against rotting by impregnation with resin oil or creosote. Such impregnated wood deters termites for many years and so is not damaged by them during this time. However, as the impregnating compound degrades (ages), termites begin to invade the surface layer and damage the item. As an on-going measure, good practice is to replace wooden sleepers with reinforced concrete ones.

2.6 Mice and Rats – the Originators of Biodamage

Some mammals, including rats and mice, may cause biodamage of materials and products. They not only cause economic damage but are also carriers of dangerous pathogens so can harm human health.

A typical feature of rodents is the characteristic structure of their jaws and teeth. The jaws are powerful and highly specialised. The upper and the lower jaws each bear a pair of teeth known as incisors which are very large, are ‘open rooted’ and grow continuously during the whole life of the animal. Rodents produce tooth enamel continuously and must wear down their incisors by gnawing. Their ends of these teeth are chisel-shaped, the front surface of each one is coated by a thick solid enamel layer, and the sides and inner walls by a thin layer. As a consequence, the incisors are ground down differentially and always remain sharp [5]. The hardness of the enamel on the Mohs scale is 5.0–5.5. The strong muscles attached to the lower jaw are responsible for the gnawing and chewing motions and create high pressure at the cutting edges of the incisors. The pressure of the cutting edge of Norway rat incisors during the gnawing of solid materials has been reported to reach 95 MPa (940 kGf/cm2) [16, 17]. Gnawing is a specific form of muscular activity for all rodents and, over time, has evolved to include gnawing which is directly associated with the act of eating and other gnawing activities such as nest construction or the grinding of incisors to ensure that they remain sharp.

It is known that mice and rats have weak sight. The visual acuity of Norway rats is just 11 arc minutes and mice have much poorer sight, whereas dogs and cats have a

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visual acuity of about 5 arc minutes and man, 26 arc seconds. Because of their poor visual acuity, rodents can only see objects clearly at close range. Rats and mice can see a matchbox-sized object clearly at a distance of 6–12 in (15–30 cm), whereas large objects such as tables or chairs can be clearly seen at a distance of several metres. Mice see other mice moving in a room at a distance of one metre or more and but must be much closer to a stationary mouse before they can see it. Hearing is important to rodents for their spatial orientation. Acoustic signals meaningful for animals easily induce their conditioned reflex.

The vibrissae (whiskers) are present on the face and mainly on the nose of a rodent. These are sensitive to touch and help the animal to identify the closeness of objects, particularly in the so-called dead zone (the space in front and beneath the nose) which the animal cannot see easily. Rodents have an excellent sense of smell, which helps them to survey their territory.

Despite their short legs, rodents can run very quickly, and can climb trees or even walls, if they have a rough surface. Only rats can swim and dive well (Figure 2.6).

Figure 2.6 Rodents. 1 Black rat; 2 House mouse; 3 Norway rat

Rodents are referred to as synanthropic (i.e., they live near to humans and benefit from their associations with them). They currently live throughout the globe, with the exception of the Arctic and Antarctic regions. The type and degree of damage caused depends on the rodent species responsible; larger species cause a greater amount of damage to a greater number of materials.

2.6.1 Rats

The rat has adapted to more different habitats than almost any other animal. It lives in tropical jungle and in tundra, on the sea shore and in mountains, in

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underground railway systems and on ships and is equally at home in houses and basements, warehouses, offices, cellars, sewage systems, attics and rubbish tips. It needs only food, water and shelter for the nest but prefers to live close to a source of food, which is why it is always attracted by human settlements, where life is easier for it. In warm climates, rats live all year round in human settlements but also away from them. In temperate climates, they live close to human habitation in the cold seasons, but may spend spring and summer further afield. However, no wild populations of rats are observed in the far north; they live near man all year round.

The distinctive physical features of rats are their relatively large size and a long thick tail, which is covered by short rigid bristles. The body of the mature animal is 5–10 in (13–25 cm) long. The hair colouring of a given species is so variable that it is not a reliable characteristic which can be used to identify the species.

The Norway rat is the biggest animal in this group, having a body length of 6–8 in (15–20 cm); the tail is always shorter than the body. Immature animals can be distinguished from mature ones because their heads and legs are larger compared with the body, and this also helps to distinguish them from mice of the same size. The ears are bald and do not reach the eyes as in most other rat species. The hind feet have rudimentary diaphragms of 1–2 mm between the toes.

The pregnant female collects material such as pieces of cotton, floss and paper to build her nest. The gestation period of the Norway rat is 23 days and this rat produces three litters per year, each of which consists of between five and nine young. The female feeds them for up to three weeks and the young rats reach maturity after two to three months.

Curious facts: Norway rats run as quickly as 6 mph (10 km/h), jump as high as 32 in (80 cm) and up to 6.7 ft (2 m), when endangered. They also can swim (the record is 17.5 miles (28 km!)), dive and climb.

The black rat is smaller in size. It is 5–6 in (13–15 cm) long and has a tail which is sometimes equal to the body length but usually longer. Sometimes the tails breaks off so cannot necessarily be used as a feature for identifying the species. The ear structure is a more reliable means of identifying the black rat. It is roundish and delicate resembling a petal and light can pass through it. The ears cover the eyes when pressed forwards. The hind feet have no rudimentary diaphragms and are always thinner, as compared with the Norway rat of the same size.

Curious facts: Interesting facts about rat stress were published in a magazine in West Germany. It appears that rats with damaged vibrissae often die as a result

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of stress. If a rat suffers heart failure as a result of being shocked, touching its whiskers can revive it (i.e., this restarts the heart). This phenomenon has not yet been explained.

Norway rats, as well as grey mice, originated in Southeast Asia, but in the eighteenth century, they began to spread from China across the world. In many instances, this occurred because they stowed away on the ships of European explorers. The Norway rat has diminished the black rat population, and is now the dominant rat in Europe and much of North America.

2.6.2 Mice

Mice are smaller than rats; their bodies are 3–5 inches (7–13 cm) in length and their tails may be either slightly shorter or slightly longer than the body. The tails are hairier than those of rats. The nose is pointed, the eyes are large and protruding and the ears are relatively large. The body is slender, and mice have long legs. The hair cover on the mouse tail is much denser than that of rats.

The house mouse has a grey or greyish-brown back and a whitish abdomen. Its body is between 2.8 and 4.3 inches (7–11 cm) long, with a tail of up to 4 inches (10 cm) in length. The upper incisors have a distinctive kink and hollow which are clearly visible when viewed from the side.

The striped field mouse is larger than the house mouse. The body is up to 5 in (12.5 cm) long, with a tail of up to 3 inches (8 cm) in length. The body is reddish-brown in colour with a narrow black strip (a ‘belt’) along the back.

The gestation period of the striped field mouse is 18–24 days. The litter size is usually 5–7, with four broods annually. Young mice are born naked, blind, deaf and helpless. They begin to feed independently after 20–25 days and become mature at the age of 2.5–3 months.

Curious facts: Mice are extremely agile and capable of climbing. Items such as table legs need to be coated with very slippery varnish to prevent mice from climbing up them. Mice can also climb up through a narrow gap between a piece of furniture and a wall by pressing their backs against one surface and their feet against the other. If it loses its balance while running across a taut rope, the mouse wraps its tail around the rope and climbs back on to it.

Among living organisms that damage materials, rodents occupy a special position, because not only do they damage foodstuffs but they also cause large amounts

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of damage to nonedible materials as a result of the gnawing that they need to do in order to grind their incisor teeth down and keep them sharp. For example the upper incisors of Norway rats grow by 2.5 mm per week, and the lower incisors by 3.45 mm. The type and degree of damage caused depend very much on the rodent species involved. Since all rodents have similar incisors, this means that, all other factors being equal, the damage caused will depend on the size of the rodent and the strength of its jaws. Thus, larger species will cause greater damage to a greater number of materials.

When they reach a source of food, rodents damage packaging, gnaw holes in the floors or walls of barns, warehouses, granaries and barns. Along with food, they damage stored fabrics, fur, footwear, plastics, furniture etc., and damage to lead water pipes and aluminium products by rats has been reported. In dwellings and other buildings, rodents use many materials to make their nests including paper, rubbish, foamed plastics, insulation materials, and rubber. The considerable damage caused by rodents to cables and wires can lead to accidents, failure of telecommunications equipment and train services, fires and can even cause human deaths. Rat damage to construction materials such as panels with metal (or other) coatings and insulating polyurethane foams, in particular, causes the loss of their heat shielding properties. They can destroy up to 30–40% of the foamed plastic heat insulating layer by gnawing channels in it.

Rodents damage goods both by gnawing and by contaminating them with excrement, urine and hair and when this occurs, microorganisms and pathogens begin to propagate in them. Rodents are carriers of at least thirty pathogens which are hazardous for man, including extremely hazardous ones such as plague, typhoid or leptospirosis.

In some cases, rodent damage can cause indirect loss; for example, damage to the outer packaging of stored goods by rats causes them to deteriorate. The damage to, or destruction of, food packaging leads to contamination of foodstuffs.

Rodent damage to materials may be caused in several ways (Table 2.1). Rodents can damage various materials in order to overcome obstacles on their way to the food and water or when burrowing. This includes damage to packaging, lead water pipes, mouldings in buildings, and cables laid underground or in buildings. They may also damage various materials in order to use them to make nests and will use any suitable material to hand, e.g. paper, fabrics, felt, films, etc.

Experiments have shown that along with paper and fabrics, rodents also used wire insulation, rubber, foamed plastics and thin wires for making nests. In the absence

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of natural materials, damage to manufactured materials increases because these are used for nest making, especially in the gestation period, when the gnawing activity of pregnant females increases.

Table 2.1 Types of rodent activities which cause biodamageBiodamage caused by rodents ‘Inedible’ (gnawing) activity

Used as food source Biocontamination: contamination by excrement, urine and hairs

Damage to packagingExploratory behaviourNest makingGrinding incisorsDamage to obstacles‘Mixed’ behaviour

Exploratory behaviour may also cause damage to materials. It is known that the occurrence of new objects in cages or areas where rodents are concentrated increases the exploratory activity and may result in damage to the objects. Also, gnawing of any object by one animal may induce other individuals to do the same.

When the young animals leave the nest, their gnawing activity increases sharply as they actively explore their environment and this results in increased levels of damage to materials and objects.

The gnawing activity may also be increased by external factors, such as the disturbance of normal behaviour, which may result in an increase in damage to materials due to ‘mixed’ behaviour. This is observed under conditions of stress, during periods of sharply increasing population, when the population structure is disturbed and competition for food and shelter is stepped up. It has been shown that if animals are transferred from a large cage to a smaller one, if established couples are separated or if animals which are unfamiliar to each other are placed in a cage together, exploratory behaviour increases in all these cases and a sharp increase in gnawing activity is observed.

Curious facts: Cases have been reported where rats have not only caused failure of electrical devices by gnawing through wires, but on some occasions have bridged disconnected electrical wires with their own bodies. This has resulted in the deaths of people who were working on the circuits at the time, and the failure of (and damage to) transformers and other electrical equipment. Rats and mice may sometimes cause accidents on electrified railways. Cases are known when a mouse has entered a transformer and thus stopped an electric train service.

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Rodents cause great damage to constructions such as dams, dykes, etc. and these must be constantly repaired to avoid their destruction and possible disasters. For instance, a dam failure in northern Italy, which was caused by rodent damage, caused a tremendous flood; in central Asia rodents have destroyed the banks of irrigation systems.

Damage to various materials and facilities by rodents results from a combination of the reasons described previously. There is a need for research in order to determine those materials and articles that are resistant to such damage.

Laboratory tests are based on the ‘enforcement’ method in which a plate of the material under test is used as a barrier to prevent the rodents from reaching food. A test cage is divided by a partition with a hole at the bottom into two equal parts. A nest, a drinking cup and an animal are placed in one part, and the food is placed in the other. The hole in the partition is then filled by a plate of the material under test, leaving a 15 mm gap beneath for rats and a 6–8 mm gap for mice. The rodents are placed in the cage for a definite time (2–3 days) prior to the test to make them acquainted with it. The first test materials will be those which are easy to gnaw, such as paper, cardboard or plastic foam. The rodents are fed 24 hours prior to the experiment beginning and the test duration is 24 hours. Water consumption is unlimited during the test. The test is be repeated after 48 hours, because if the tested material is resistant and the rodents are unable to reach the food source on the other side of the partition, they lose up to 20% of their body mass per day and so would die if the test was repeated too quickly [5].

To obtain more accurate results, every material should be tested three times. Materials which are not damaged by rodents must not be tested several times using the same animals, because they remember these materials and do not touch them any more after the first test. The materials which cannot be damaged must be alternated in the tests with those which are easily damaged by rodents, otherwise the animals will develop a passive avoidance response and will stop gnawing the obstacle.

Table 2.2 shows data on the resistance of materials to rodent damage. The tests show that rodents damage many materials including wood, paper, cardboard and leather. Plastics, other than very hard materials, are also susceptible to rodent damage as are rubbers, regardless of their chemical composition. Sample thickness, density and other physicochemical characteristics do not affect the level of damage. Foamed plastics, irrespective of their chemical composition, are also damaged by gnawing rodents. Since these are used for many goods, thorough control of rodents in warehouses must be implemented. Up to 40–50% of the initial mass of urethane foams, polystyrene foam and other materials was destroyed by gnawing. The test plates were gnawed from all sides and pieces of these materials were then used in nests. For foam plastics,

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the damage intensity depended on the density of the material: the lower the density, the greater the loss of mass. This dependence was more clearly observed in the case of small rodents.

Table 2.2 Resistance of materials to rodent damageMaterial Extent of deterioration by rodents

Large Small

Natural, laminated, pressed wood 3–4 3–4

Paper, cardboard 4 4

Nonwoven materials, including glass wool, glass fibre mat

41 41

Yarn, threads, ropes, cable ropes from cotton, linen, silk, synthetics, glass fibre

41 41

Fabrics (natural, coated and impregnated): cotton, linen, silk, wool, synthetics, glass fibre

41 41

Real leather 4 4

Artificial or synthetic leather 4 4

Plastics (such as PE, polypropylene, PVC, fluoropolymers and polyacrylates)

3–4 2–4

Filled plastics 2–4 1–3

Foamed plastics 4 3–4

Rubbers 4 3–4

Paint coatings: on wood 4 3–4

Steel plates 3–4 1–2

Aluminum alloys 2–4 1–4

Glass fabric 4 4

Polystyrene 4 4

Other plastics not mentioned above 2–3 2

Laminated fabrics 2–3 1

The test results are as follows: 0 – the material is not damaged; 1 – insignificant tooth marks on the plate surface; 2 – the surface is damaged; 3 – the surface is seriously damaged, but not gnawed through; 4 – the plate is gnawed through.

Note: 41 – rodents have used materials for making nests.

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Laboratory tests of cables and wires indicate that their stability to rodent damage depends on the external cover material, the diameter, the presence of a protective outer layer and the rodent species involved. Outer coatings of steel wires or copper tapes protected cables from rodent damage. Small rodents do not damage steel wire coverings, and rats damage them only on small diameter cables. Cables and wires covered with plastics, rubber or fibrous insulation, however, were damaged by rodents which grawed through the insulating cover of electric cables, exposing live wires. The diameter of a cable is important for its resistance to rodent attack. Rats gnawed through cables up to 17 mm in diameter and considerable damage was also observed for cables of 24–29 mm in diameter. Small rodents cut wires and cables of up to 6 mm and considerably damaged cables of up to 15 mm in diameter, but little damage was done to cables with diameters greater than 20 mm.

Paint coating tests indicate that their stability is determined by two factors: the resistance of the material itself to rodent attack and the adhesion of the paint coating to the substrate. Unstable supports (foam plastic, wood, etc.) are damaged together with the coating. In case of poor adhesion, the rodents damage the coating and expose the support.

The possibility of rodent damage to a material depends on the surface of the material (smooth or rough), its hardness and its structure (filled, porous, viscous, etc.). In tests, rodents easily damaged plastic foams, when the hole in the partition separating the food and nest sections of the cage was completely closed by the plate, because the animals were able to gnaw the porous surface using their incisors. The same plastic foam coated by epoxy resin was not damaged by rodents, because the incisors could not penetrate the smooth surface. Joints, projections or holes on materials also make it easier for rodents to damage a material.

Hardness is essential for material stability. A study of three packing materials (PVC, various acetates and polycarbonate) for possible damage by rats demonstrated that the extent of the damage was correlated with hardness. The hardest material (polycarbonate) showed the least damage [5, 6].

Curious facts: In many ways, rats are really extremely vulnerable. They are instinctively highly suspicious of anything new or unusual and if a trap, or simply a brick, is placed on their run, they will disappear for a couple of nights. It is the opinion of the Scottish scientist Canby that if new objects are placed regularly on rat runs, they will leave the territory within a month.

Rats dislike ultrasound. The sound frequency of 20 kHz makes them nervous, they become frightened of one another and attack each other.

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Rodents eat their preferred foods first. For instance, when samples of margarine and butter were left out overnight, they ate the butter but the margarine remained untouched. If there is no choice, they will eat any food, including waste.

A study carried out by researchers at Moscow State University shows that rats are fond of alcohol, and 20–25% of them may potentially become addicted to it.

2.6.3 Protection of Materials against Rodent Damage

No methods have yet been developed which will directly protect all materials against rodent damage because rodents cause damage in different ways. The current methods aim to decrease the rodent population as much as possible, thereby reducing the extent of the damage to materials and facilities [5, 6].

The range of measures for rodent control is called deratisation (rat extermination). Rodents are controlled in two ways: the implementation of prophylactic measures (hygiene or technical), and extermination which includes three methods of control: chemical, physical (mechanical) and biological.

The success in controlling of rodents depends on the proper organisation of procedures and starts with the broad implementation of prophylactic measures, which are then accompanied by destructive control measures. When the rodents have been cleared, destructive methods are frequently discontinued but prophylactic measures are maintained.

2.6.3.1 Prophylactic Measures

There are three types of prophylactic measures:

• Hygiene measures, which include the elimination of food and areas of shelter for rodents;

• Construction of various physical obstacles to prevent rodents from gaining access to premises;

• Application of various compounds which repel rodents to protect buildings, food packaging electric wire coverings etc.

Searching for repellents is a complicated problem. Substances which are candidates for repellents must a) be nontoxic for humans; b) must not lose their ability to repel

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rodents when added to materials which need to be protected from rodent attack; c) must not change the properties of the material itself and d) must not change when impacted by environmental factors. The mechanism of action of repellents has not yet been fully studied. This hinders the search for new substances, which requires a complex approach and the cooperation of chemists, technologists and biologists [18–28].

The zinc salt of dimethyldithiocarbamic acid is an effective repellent for rodents and has low toxicity to humans. When buildings are treated with this repellent, the rodents leave and do not return there for 12 months. The damage rate of the surfaces of various materials treated with this compound (paper, plywood, cardboard, coarse calico) decreases abruptly, as compared with control samples.

The most effective repellents are organotin compounds, suggested for adding to paints and pulp for packaging cardboard manufacture.

2.6.3.2 Physical Methods

Recently, methods of protecting materials and buildings from rodent attack by using high-frequency sound and ultrasound have been widely publicised but studies have shown that after a short-term positive effect the rodents acquire tolerance and the repellent effect reduces to zero.

Curious facts: Various methods have been tried in the struggle against rats. In Latin America, boys were allowed to go to the cinema for free, if they brought a batch of rats’ tails to the cashier. On the Island of Java, newly married couples have paid a tax of 25 rats’ tails to the government, and it was only possible to obtain a passport by contributing five rats’ tails in addition to the normal fee.

2.6.3.3 Chemical Methods

Most of the compounds which are used to control rodents are synthetic ones. The important advantage of chemical agents is their relative stability that allows them to be stored for a long time, as well as produce a consistent rodenticidal effect under normal environmental conditions. The main disadvantage of chemical rodenticides is their relatively high toxicity and the associated danger for people and for beneficial animals.

The main methods which are currently used to deliver chemical rodenticides to rodents are:

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• Poisoned food baits, in which a rodenticide is mixed with a food product which is quite attractive for rodents.

• Liquid poisoned baits, i.e., the use of solutions or suspensions of the poison in water, milk and other liquids.

• Dusting, i.e., the application of poisonous powders on to burrow exits, paths, and places in which the rodents travel.

• Fumigation, i.e., the supply of a gaseous poison to an affected area or rodent burrow in order to kill the animals.

Rodenticides may be divided into phytotoxins and synthetic poisons. Phytotoxins include a limited number of compounds including strychnine, red squill and some others. There is a wide variety of synthetic rodenticides and these are divided into two main groups each characterised by the way in which they act on the living organism; these are preparations which have an acute action and those with a chronic action (anticoagulants).

Curious facts: Red squill was one of the first poisons widely applied to control rats. It was officially accepted for this purpose in 1718 and was used on all continents until recently, when other more efficient agents became available. Dried and ground squill was added to foodstuffs or mixed with grains, which were then put into places that were known to contain rats.

Until the end of the seventeenth century, only phytotoxins were used but after that, the use of virulent poisons such as arsenic and strychnine became widespread. Rodents were also controlled by hydrocyanic acid, first in the United States and then in England and Italy. The use of barium and phosphorus compounds began in the middle of the nineteenth century, followed by poisons such as zinc phosphide and thallium sulfate at the beginning of the twentieth century. In most countries, by the late 1940s, highly toxic compounds of arsenic, phosphorus, fluorine, thallium and barium were used to kill rodents but these were just as toxic to other warm-blooded animals.

Acute action poisons are characterised by the comparatively quick onset of poisoning in the animal after a dose of the agent has been administered. Initial symptoms of poisoning may already be observed a few hours after the poison has been ingested. If rodents are poisoned very rapidly it makes the others suspicious and they refuse to eat bait containing that particular poison, or indeed, any other poison.

The acute action poisons include zinc phosphide, thiosemicarbazide, fluoroacetamide, barium and sodium fluoroacetate. The poisoned bait is applied to burrows, in baiting boxes, straight on to paper or cardboard and in feeders. Recently, long-acting

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reservoirs of poison such as baiting boxes are widely recommended, because laying a bait to burrows may not provide the same efficiency.

When operating with poisoned baits, the possibility of ‘defensive reflex’ or acquired tolerance to poison in the rodent population must be taken into account. When long-acting baits containing such active agents as thiosemicarbazide are used, the rodents which do not receive a lethal dose acquire resistance to this poison and in order to kill it in future, the dose must be increased three to four-fold or the rodenticide must be changed.

Chronic action poisons (anticoagulants) are characterised by a long latent period, and a slow development of the poisoning process as regular extremely low doses of the poison are ingested by the animal. These compounds usually accumulate in the animal and gradually cause considerable biochemical and pathological changes and death. If there is no water in a room, then it is very effective to place poisoned water there, and animals will readily drink it. Both quick action and chronic action poisons (anticoagulants) can be administered in this way.

The most effective rodent control is obtained using long-acting reservoirs of poison consisting of flour-based bait containing anticoagulants. Such bait lasts well and remains attractive to rodents for a long time, so gives good results.

When the intention is to protect an object for a long period of time, only the least-toxic bait may be used. For the purpose of rodent extermination in a large area, highly toxic poisons such as ratindan, zinc phosphide or fluoroacetamide may also be applied for a short period.

Curious facts: The discovery of α-naphthylthiourea by Richter in 1940 provided a breakthrough. This rodenticide was specific for Norway rats, the most widespread and hazardous species of rodents. At first, its application gave excellent results but it was shown that rats which received a nonlethal dose of this poison become resistant to it and so were then unaffected by it.

By 1940, rather than searching for highly toxic compounds to use as rodenticides, scientists began studying another group of substances, the anticoagulants. When entering an organism these compounds do not, at first, cause immediate signs of poisoning, but their toxicity increases when they enter the bloodstream. As they accumulate, these compounds prevent the blood from coagulating, increase the permeability of the blood vessel walls, cause multiple haemorrhages and the animal eventually dies. However, after five years of using such poisons, the rodents demonstrated their amazing ability to adapt and began to avoid eating the bait.

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By that time new rodenticide anticoagulants of the second generation had been developed: brodifacoum and bromadiolone. Their feature is that the lethal dose of poison is included in a small amount of bait. However, some investigators concluded that these anticoagulants should not be used in places where resistance to even one of them is detected.

2.6.3.4 Mechanical Methods

Mechanical methods of exterminating rodents include traps, pitfall traps, electrical traps and fencings; the use of large areas of adhesive, and flooding rodent burrows. Distributing and collecting devices, such as traps, is a labour intensive process, so mechanical methods are combined with chemical ones.

2.6.3.5 Biological Methods

For the control of rodents their natural enemies such as cats, dogs, birds and microorganisms (pathogenic for the rodents, but nonhazardous for people and pets), are used. The application of a bacteriological method to control rodents was assumed possible when, by the end of the nineteenth century, microorganisms pathogenic for rodents and nonhazardous for people and useful animals were discovered. The biological method is not widely applied. The bacterial method is not highly efficient for the control of Norway rats (about 60–80% of rats die). However, the control of house mice gives good results (about 90–100% of them die). Microorganisms of the Salmonella group are used for this purpose. After eating the infected bait, the rats and mice fall ill, then infect other healthy animals and the majority die within two to three weeks. Properly applied, the use of the biological method can give excellent results.

References

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4. D.P. Zhuzhikov, Why the Cockroaches Are Dangerous, Sputnik Publishing House, Moscow, Russia, 2005. [In Russian]

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6. Protecting Materials and Equipment from Damage Caused by Insects and Rodents, Ed., N.A. Plate, Scientific Council for Biological Damage of the USSR Publishing House, Moscow, Russia, 1984. [In Russian]

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17. Animal Life, Eds., M.S. Gilyarova and F.N. Pravdina, Education Publishing House, Moscow, 1984, p.3. [In Russian]

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22. G.E. Zaikov, A.L. Buchachenko and V.B. Ivanov, Polymer Aging at the Cutting Edge, Nova Science Publishers, New York, NY, USA, 2002.

23. K.Z. Gumargalieva and G.E. Zaikov, Biodegradation and Biodeterioration of Polymers. Kinetical Aspects, Nova Science Publishers, New York, NY, USA, 1998.

24. S.A. Semenov, K.Z. Gumargalieva and G.E. Zaikov, Biodegradation and Durability of Materials Under the Effect of Microorganisms, VSP International Science Publishers, Utrecht, The Netherlands, 2003.

25. A.Ya. Polishchuk and G.E. Zaikov, Multicomponent Transport in Polymer Systems, Gordon & Breach, New York, NY, USA, 1996.

26. Yu. V. Moiseev and G.E. Zaikov, Chemical Resistance of Polymers in Reactive Media, Plenum Press, New York, NY, USA, 1987.

27. N.M. Emanuel, G.E. Zaikov and Z.K. Maizus, Oxidation of Organic Compounds. Medium Effects in Radical Reactions, Pergamon Press, Oxford, UK, 1984.

28. A. Jimenez and G.E. Zaikov, Polymer Analysis and Degradation, Nova Science Publishers, New York, NY, USA, 2000.

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