Basic Entomology X 129

Bob Polomski and Eric Benson, Ph.D.

Chapter 6

Basic Entomology

Learning Objectives

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Basic Entomology X 130

Basic Entomology

Insects are among the oldest, most numerous, and most successful creatures on earth. About one million different species are known to exist, occupying every conceivable habitat except for the open ocean. Insects can be found in or on animals, plants, soil, streams, lakes, ocean shores, in wooden structures and furniture, and in stored grains and other foods.

While insects that cause problems for humans receive the most publicity, the vast majority are either beneficial or harmless. Insects pollinate most fruits and vegetables. They provide food for many animals. Some produce useful products such as honey, wax, shel-lac, and silk. In addition, some insects are beneficial because they feed on other insect pests.

Worldwide, only about one percent of known insect species (or about 10,000) are economically de-structive pests. These harmful insects destroy crops in the field and in storage. About one-sixth of the world’s food crops are eaten by insects. They also transmit dis-eases to crops, livestock, pets, and humans.

Insects and Their RelativesInsects belong to the phylum Arthropoda, which

means “jointed legs.” This phylum includes spiders, ticks, crabs, and lobsters. Arthropods have segment-ed bodies and a skeleton outside of the body, which is called an exoskeleton. There are a number of arthropods that are mistakenly called insects. These insect relatives include mites and spiders (arach-nids), centipedes (chilopods), sowbugs and pillbugs (crustaceans), millipedes (diplopods), and snails and slugs (molluscs). Illustrations and brief descriptions of these insect relatives can be found in the “Com-mon Noninsects” section on p. 142.

Insect AnatomyFor an organism to be classified as an insect, the

adult form must have six legs and three distinct body regions (Figure 6.1). In addition, most (but not all)

adult insects have one or two pairs of wings located on the second or third segment of the thorax.

Jointed legs (3 pairs)The most important characteristic of insects is

the presence of three pairs of jointed legs. These are almost always present on adult or mature insects and are generally present in the other stages as well. In addition to walking and jumping, insects often use their legs for digging, grasping, feeling, swimming, carrying loads, building nests, and cleaning parts of the body. The legs of insects vary greatly in size and form and are used in classification (Figure 6.2).

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Basic Entomology X 131

Distinct body regionsThe adult insect’s body is made up of three

parts: head, thorax, and abdomen (Figure 6.1). An insect’s body is not supported by a bony skeleton but by a tough body wall or exoskeleton. The tough covering of skin is referred to as the cuticle. The cuticle contains a layer of wax that determines its permeability to water (even to insecticides) and pre-vents desiccation or drying. The cuticle of each seg-ment is formed into several hardened plates called sclerites, separated by infolds or sutures which provide flexibility. The cuticle of the immature or larval stage is not usually as hardened as that of the adult.

The thorax is made up of three segments: pro-thorax, mesothorax, and metathorax. Each of these segments bears a pair of legs. The wings are at-tached to the mesothorax and metathorax, never to the prothorax or first segment.

The abdomen may have 11 or 12 segments, but in most cases they are difficult to distinguish. Some insects have a pair of appendages at the tip of the abdomen. They may be short, as in grasshoppers, termites, and cockroaches; extremely long, as in mayflies; or curved, as in earwigs.

Insects breathe through pores in their abdomens called spiracles. Some insecticides enter the insect pest’s body through the spiracles.

Antennae (1 pair)The main features of an insect’s head are the

eyes, antennae, and mouthparts. The antennae are a prominent and distinctive feature of insects.

Insects have one pair of antennae located on the adult’s head usually between or in front of the eyes. Antennae are segmented, vary greatly in form and complexity, and are often referred to as horns or “feelers” (Figure 6.3). They are primarily organs of smell but serve other functions in some insects.

WingsMany insects develop wings as adults, and so

are recognized as the only winged arthropods. The names of some of the insect orders end in “-ptera,” which comes from the Greek word meaning “with wings.” Thus, each of these names denotes some feature of the wings. Hemiptera (true bugs) means half-winged; Hymenoptera (ants, bees, and wasps) means membrane-winged; Diptera (flies) means two-winged; and Isoptera (termites) means equal-winged.

The venation or the arrangement of veins in wings is different for each species of insect; thus, it

serves as a means of identification (Figure 6.4). Systems have been devised to designate the venation for descriptive purposes. Wing surfaces may be covered with fine hairs or scales, or they may be bare.

MouthpartsAn insect’s most remarkable and compli-

cated structural feature is its mouth. Many variations exist in the form and function of insect mouthparts. And although insect mouthparts differ considerably in appearance, the same basic parts are found in all types. Most insects are divided into two broad cat-egories by mouthpart type: either adapted for sucking or chewing (Figure 6.5). One excep-tion is the sponging mouthparts on many spe-cies of flies.

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Basic Entomology X 132

Insects with chewing mouthparts have man-dibles with teeth and strong jaws. Chewing larvae and adults bite and chew plant parts creating holes and tunnels in leaves, stems, twigs, and fruits (Fig-ure 6.6). Chewing damage is done inside stems and branches by borers, inside leaves by miners, in fruits, nuts, or seeds by worms or weevils; and on leaves by defoliators or skeletonizers.

Some common examples of in-sects that cause injury by chewing include armyworms, cabbageworms, Colorado potato beetles, grasshop-pers, Japanese beetles, and fall web-worms

Insect pests with sucking mouthparts pierce plants with slen-der, sharp-pointed mouthparts called stylets and suck plant sap. These insects, which include aphids, leaf-hoppers, scale insects, true bugs, scale insects, thrips, and whiteflies, feed on photosynthates, or the products of photosynthesis (sugars and other complex carbohydrates). The withdrawal of the sap results in minute white, brown, or red spotting on leaves, fruits, or twigs; curling leaves; deformed fruit; or general wilting, browning, and dying of the entire plant. Some of these insects inject toxic salivary products into the plant that results in discolored leaves and dieback of woody plant parts.

Some insects, such as aphids and leafhoppers, are vectors or transmit-ters of diseases, especially viruses.

When they feed on a diseased plant, they transmit the disease to another host plant when their saliva mixes with the sap.

The damage done by sucking mouthparts sel-dom results in loss of plant tissue. Rather, holes or deformed growth occur. Pests with chewing mouth-parts remove plant tissue. Knowing the difference in damage caused by chewing or sucking insects is the first step in pest identification.

The mouthparts of larvae tend to be different from the adults of the same species because they feed on different foods. Caterpillars have chewing mouthparts for consuming leaves and other vegeta-tion. In contrast, adult moths or butterflies feed on liquids, such as nectar, so they are equipped with a sucking tube that forms siphoning mouthparts.

Insects that attack plants below the soil surface have chewing or sucking mouthparts. The attacks

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Basic Entomology X 133

differ from the above-ground forms only in their position with reference to the soil sur-face.

Some subterranean insects spend their entire life cycle below ground. For example, the woolly apple aphid, as both nymph and adult, sucks sap from the roots of apple trees, causing the development of tumors and subsequent decay of the tree’s roots. Other sub-terranean insects have at least one life stage above ground. Examples include wireworms, root maggots, strawberry root weevils, blackvine weevils, Japanese beetles, and grape and corn rootworms. The lar-vae are root feeders while the adults live above-ground.

Insect Growth and Development

Every insect begins life as an egg; however, the eggs of some harmful pests, such as aphids, hatch within the body of the female parent and the immatures are born as living young insects. In some insects, the egg may or may not need to be fertilized by sperm to devel-op. Females can produce more females (or males, in some cases) by a process called parthenogenesis. Bees, ants, wasps, and aphids are notable examples of insects that can reproduce by parthenogenesis. When males are required, sexual mating takes place.

Insects grow by shedding their outer skin or exoskeleton in a process called molting. Insects increase in size and appearance with each molt. Immature insects may molt many times, some six times or more.

This change in shape and appearance from the juvenile to the adult stage is called metamor-phosis (Figure 6.7). The term is a combination of two Greek words: “meta,” meaning change, and “morphe,” meaning form. It is commonly defined

as a marked or abrupt change in form or structure and refers to all stages of development. Related arthropods such as spiders, mites, and centipedes also undergo metamorphosis; however, the changes in shape of spiders and lower insects are much less dramatic than the complete change in shape of the more developed kinds of insects. This change is called complete metamorphosis. Beetles, moths, butterflies, wasps, ants, and flies all go through four very different stages in order to complete develop-ment: egg, larva, pupa, and adult.

The larva is often the damaging stage because it is basically a feeding machine. Over time, the larva or nymph sheds its exoskeleton (molts) at various stages of growth because it outgrows the hard cover-ing or cuticle. Most insects do not grow gradually

Nonmetamorphosis

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Orders: Collembola Diplura Protura Thysanura

Orders: Dermaptera Hemiptera Homoptera Isoptera Orthoptera Thysanoptera

Orders: Ephemeroptera Odonata Plecoptera

Orders: Coleoptera Diptera Hymenoptera Lepidoptera Neuroptera Siphonaptera

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Basic Entomology X 134

In some aquatic insect species, such as dragonflies, the nymphs are gill-breathing, making them more different in appearance, and in their habitat, compared to adults. Insects in this group are sometimes referred to as having incomplete metamorphosis, and the nymphs are sometimes called naiads.

The most primitive insects go through very little change between stages. The adults lack wings, so they closely resemble the nymphs. Most experts refer to this as non-metamorphosis.

A life cycle from the egg to the production of an egg by the subse-

quent adult stage is called a generation. Many insect species only have one generation each year, while others have several especially in the south where warm seasons last longer. A single generation may require many years, such as 17 years for some cicadas, one of the longest-lived insects in North America.

A new generation does not always begin with the egg stage in the spring. However, in any given region, an insect species normally overwinters in the same stage each year. Insects are cold-blooded and their body temperature is influenced by the sur-rounding temperature of their environment. Winter in South Carolina offers gardeners some respite from insects. A majority of insects are active during the warmer months of the year or during warmer parts of the day.

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Identifying the hundreds of thousands of known insect species would be impossible if they were not organized around a standard classification system. This system of grouping organisms is based on the degrees of similarity among them. It ranges from the broad-based Kingdom to the more specific Species level as shown below:

Kingdom Phylum Class Order Family Genus

Species/Specific epithet

but by stages. When their exoskeleton gets too tight, it splits open and the insect crawls out, protected by a new and larger exoskeleton that has formed under-neath the old one. The stage of life between each molt is called an instar. Following each molt, the in-sect increases its feeding. The number of instars, or frequency of molts, varies considerably with species and, to some extent, with food supply, temperature, and moisture.

Feeding by adults may be destructive as well. The larval and adult stages of many species feed on dif-ferent hosts or different parts of the host. The pupal stage does not feed and appears to be inactive, but is actually in a very active stage of metamorphosis.

The lower insects undergo a slight change of shape which is called simple metamorphosis. True bugs, aphids, grasshoppers, termites, earwigs, and some aquatic insects, go through only three stages in order to complete development. These are egg, nymph, and adult. Nymphs and adults closely resemble each other, except the nymphs are smaller in size and lack wings. In these species, the adults and nymphs usually feed on the same host or host parts.

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Insects as Transmitters of Plant Diseases

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Table 6.1

Basic Entomology X 135

This hierarchical classification system is also used to identify plants (Ch. 3, “Basic Botany”). At the highest level, most organisms are divided into two kingdoms: animal and plant. The animal king-dom has major divisions known as phyla (phylum is singular). Several of the following phyla contain agricultural pests:

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:WLJPÄJ�Insect OrdersThe phylum Arthropoda is divided into classes.

Table 6.2 describes a few of the more important classes and presents characteristics used to distin-guish between the groups. Insects belong to the Class Hexopoda. The Class Hexopoda is further subdivided into 31 categories called orders. Each order may contain dozens, hundreds, or thousands of species that share similar anatomical features or body parts. Some examples of insect orders include:

Coleoptera: beetles and weevilsDermaptera: earwigsDiptera: Flies, mosquitos, gnats, and midgesHemiptera: true bugs, leafhoppers, aphids,

scales, whitefliesHymenoptera: Ants, bees, and waspsIsoptera: termitesLepidoptera: butterflies and mothsNeuroptera: lacewings, antlions, etc.Odonata: damselflies and dragonfliesOrthoptera: crickets, katydids, and grasshoppersThysanoptera: Thrips

Body Pairs Class Examples Segments of Legs Agricultural Importance

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Table 6.2Classes of the phylum Arthropoda.

The most important orders for gardeners are listed in Table 6.3. Not all of the insects in this table are plant-feeding pests, even when you find them on a plant. For example, insects in Coleoptera, Dip-tera, Hymenoptera and Neuroptera can be found on plants, as parasites or predators of plant-feeding in-sects, pollinators, or scavengers of dead vegetation or materials left behind by other insects.

Insect orders are subdivided into smaller groups known as families, genera, and species. The fam-ily is a more finite grouping of very closely related insects. Family names end with “idae.” Aphidae (aphids), Aleyrodidae (whiteflies), and Chrysomeli-dae (leaf beetles) are examples of families of insects.

Families are further subdivided into genera and species. These are usually the most finite levels of the classification system. Consider these examples for classifying two insects:

Japanese beetleOrder: Coleoptera Family: Scarabeaidae Genus: Popillia Species: japonica

Euonymus ScaleOrder: Hemiptera Family: Diaspididae Genus: Unaspis Species: euonymi

A majority of insect species have common names, which are often associated at the genus level. Most commonly found insects also acquire common names, and sometimes one species has several com-mon names. For example, Helicoverpa zea, when found on corn, is called the corn earworm. When

Basic Entomology X 136

Ento-terminology

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Basic Entomology X 137

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Table 6.3

Order Common Name Metamorphosis Mouthparts Wings

Orders of the class Hexopoda encountered in the garden and landscape.

it is found on tomatoes, it is called the tomato fruit-worm, and on cotton it is called the cotton boll-worm.

Common names are often used to refer to large families or orders of insects. For example, the order Lepidoptera refers to butterflies and moths, and the order Coleoptera refers to “beetles.”

Common insect orders in the home and gardenColeoptera: Beetles and Weevils (Figure 6.8)

-eton.

pair hardened and the inner pair membranous. (A few beetles are practically wingless, and some have only an outer hard pair of wings.)

the thorax with no legs on the abdomen. (Wee-vil larva lacks legs on the thorax).

of harmful insect species.Beetles are common insects (about 40% of all

insect species), but only a few are garden pests. Flea beetles, wireworms (click beetle larvae), cucumber beetles, vegetable weevils, and green fruit beetles

7YVIHIS`� ���VM�PUZLJ[�PUQ\Y`�[V�WSHU[Z�PZ�JH\ZLK�I`�MLLKPUN��I\[�WSHU[Z�JHU�HSZV�IL�KHTHNLK�^OLU�PU�sects oviposit�VY�SH`�LNNZ���-VY�L_HTWSL��[OL�WLYPVKPJHS�JPJHKH�KLWVZP[Z�LNNZ�PU�VUL�`LHY�VSK�NYV^[O�VM�MY\P[�HUK�MVYLZ[�[YLLZ��ZWSP[[PUN�[OL�^VVK�ZV�ZL]LYLS`�[OH[�[OL�LU[PYL�[^PN�VM[LU�KPLZ���(Z�ZVVU�HZ�[OL�`V\UN�OH[JO��[OL`�KLZLY[�[OL�[^PNZ�HUK�JH\ZL�UV�M\Y[OLY�PUQ\Y`�[V�[OL�WSHU[�

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Plant Injury Caused by Oviposition

Basic Entomology X 138

are common in South Carolina home vegetable gardens. Boring beetles infest trunks and branches of fruit and nut trees. Adult pest beetles may feed on the same crop as their larvae, unlike other pest groups, such as caterpillars (larval stage of butterflies and moths) and maggots (fly larvae) where the adult stage does little damage.

Ladybird beetles (ladybugs) feed on a wide range of pests including aphids, scale insects, insect eggs, mites, and other small insects.

Dermaptera: earwigs (Figure 6.9)

in color.

forceps on the abdomen. The adults have small

wings and all earwigs, young and adults, have curved pinchers at the end of their bodies (abdomen). They usually use their pinchers to protect themselves from preda-tors, but in some cases, they may use them to catch prey.

membranous, “ear-shaped” inner wings.-

pearance.They are generally considered harmless

creatures. Earwigs are active at night and will remain hidden under mulch, boards, rocks, woodpiles, and other cool damp places. Most earwigs only eat decaying plant material or dead insects.

The European earwig is the most com-mon species found in South Carolina and can be a nuisance. The striped earwig is another southern species that can be found in agricultural fields and gardens. These beneficial insects prey on many important pests, such as aphids, scales, and mites.

+PW[LYH!��ÅPLZ��TVZX\P[VLZ��NUH[Z��HUK�midges (Figure 6.10)

-ally soft-bodied and often hairy.

piercing (mosquito) mouthparts.-

ing mouthparts.

house fly and relatives, have no head capsule, possess mouth hooks, and are called maggots; lower forms such as mosquito larvae and rela-tives have a head capsule.

Order Dermaptera Figure 6.9

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Insects in the Order Coleoptera. Figure 6.8

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Basic Entomology X 139

structive pests because they often remain unnoticed until they’ve become well-established. They get their name from the protective fish scalelike covering produced by the tiny insect, which is about the size of a pencil tip.

Scale insects anchor to plant parts by their piercing-sucking mouthparts and feed on plant sap. Individual scales may look like oval or rod-shaped bumps, sometimes resembling bark or buds. They range in color from white, yellow, grey, brown to black. These insects can occur on leaves, stems, branches or trunks, and occasionally on fruit.

There are two types of scale insects. Soft scales secrete a thin, waxy layer over themselves, which cannot be separated

from the insect’s body. When you dislodge a soft scale with a pin or sharp pencil point, look for the telltale shiny spot of honeydew. Legs and antennae are attached to the underside of the shell.

Figure 6.10

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Insects in the Order Diptera.

/LTPW[LYH!��:[PUR�I\NZ��WSHU[�I\NZ��ZX\HZO�I\NZ��boxelder bugs, aphids, cicadas, leafhoppers, TLHS`I\NZ��ZJHSL�PUZLJ[Z��HUK�^OP[LÅPLZ��-PN\YL�6.11)

pathogens.

are egg, nymph, and adult.-

parts.

both damaging, if the species is a pest.

sized insects; cicadas may be large and hard-bodied.

insect pests.

Aphids are soft-bodied insects that range in color from green, yellow, red, grey, or black. They suck the juices from leaves and stems causing stunted or deformed buds and flowers, and sometimes curled or puckered leaves.

Mealybugs are oval-shaped and covered with a white, woolly coat. They feed on plant sap and exude honeydew. Look for them in the stem crevice and leaf joints.

Scale insects are highly de-

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Cicada Scale insects

Members of the Order Hemiptera. Figure 6.11

Basic Entomology X 140

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Ant

Insects in the Order Hymenoptera. Figure 6.12

nymphs called “crawlers.” The oval, flattened crawl-ers wander for a short distance before permanently settling down to feed. After their first of four molting stages, the nymphs lose their legs and antennae and look like tiny scale insects with a flattened, oval ap-pearance and covered with a waxy secretion. There are three nymphal stages that feed on the plant spaced at two to four-day intervals. The pupal stage lasts about a week. Both adults and nymphs, which are usually found on the undersides of the leaves, suck phloem sap with their piercing and sucking mouthparts. Their feeding results in yellowed or mottled leaves and reduced plant vigor. Leaves may shrivel up and drop prematurely. Similar to aphids, mealybugs, and soft scale insects, whiteflies excrete honeydew as they feed. This sticky sugary solution collects dust and supports the growth of black sooty mold fungi. They produce many generations per year.

/`TLUVW[LYH!��HU[Z��ILLZ���OVYU[HPSZ��ZH^ÅPLZ��wasps, (Figure 6.12)

pairs of legs on thorax and more than four pairs of legs on abdomen (some sawflies).

adults.

harmful insects.

Isoptera: Termites (Figure 6.13)

hundreds to thousands of individuals comprising a caste system of workers, soldiers, reproductives, and winged forms known as alates.

Because they consume large amounts of plant sap, soft scales excrete a sticky, sugary liquid called “honeydew” as a by-product of their feeding. In humid environments the shiny, sticky leaves may be colonized by sooty mold fungi which feed on the honeydew, imparting a black soot-like coating on the leaves. Large patches of sooty mold that black-en leaves and stems are often what draws attention to a scale problem.

Armored scales secrete a hard, lacquered cover-ing over their bodies. This cover is not attached and can usually be separated from the scale’s body. They typically are smaller than soft scale, about 1/16 to 1/8 inch in size. Armored scale insects do not excrete honeydew, therefore, do not support the growth of sooty mold.

Scale insects produce eggs that hatch into tiny mobile “crawlers” or nymphs. They move around the plant seeking suitable sites to feed, settle down, secrete their scale covering, and then mature to adulthood.

Some species overwinter as eggs beneath the dead female’s cover and hatch in the spring; others overwinter as fertilized females and resume feeding in the spring, when they lay eggs and die.

Scales are difficult to control. Pick off the adults by hand or with a pair of tweezers. Small populations can be killed with a cotton-tipped swab dipped in rubbing alcohol. Prune out heavily in-fested limbs.

Pesticides are most effective on the crawlers. To detect them, attach a piece of double-sided adhesive tape to a stem above an infested area in early spring before new growth begins. Examine the tape with a magnifying class to identify the specks.

There are 1,200 described species of whiteflies that attack a wide array of agronomic, vegetable, and ornamental crops. Their name is derived from the white, powdery wax that is secreted from their ab-domen to cover the adult’s wings and body.

The tiny, white mothlike adults (about 1/12 inch long) usu-ally lay between 30 and 500 tiny, white spindle-shaped eggs, usually on the undersides of the leaves of new growth. The creamy yellow eggs turn dark gray after 24 hours. They hatch within 5 to 7 days into inconspicuous, translucent white

Basic Entomology X 141

subterranean termites and the imported Formosan subterranean termite.

Native subterranean termites are common throughout the state. However, Formosan subter-ranean termites are known to occur mainly in the coastal counties, up to Charleston county. A ma-ture Formosan subterranean termite colony may be comprised of millions of workers in contrast to a native colony that may support several hundred thousand workers. Because of their sheer numbers, Formosan subterranean termites are considered the most destructive termites.

3LWPKVW[LYH!��I\[[LYÅPLZ��TV[OZ��ZRPWWLYZ��-PN\YL�6.14)

membranous wings covered with small scales.

Adults feed on nectar.

color, and voracious feeders.-

men as well as the thorax.

5L\YVW[LYH!��HSKLYÅPLZ��HU[SPVUZ��KVIZVUÅPLZ��K\Z[`�^PUNZ��SHJL^PUNZ��THU[PKÅPLZ��ZUHRLÅPLZ�(Figure 6.15)

6KVUH[H!��KHTZLSÅPLZ��+YHNVU-ÅPLZ!���-PN\YL������

-es, and other small insects.

veined wings. Damselflies fold their wings over their backs at rest; dragonflies keep their wings out horizontally.

Comparison of a termite swarmer and a swarming ant.

Figure 6.13

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Order Lepidoptera. Figure 6.14

adult stage. Subterranean termites feed on cellulose-con-

taining materials, such as dead trees. They digest wood with the help of microorganisms which live in their digestive tracts.

Termites become a problem when wooden struc-tures are built over or near their colonies. They build earthen shelter tubes from the ground into the structure for protection from predators and to help maintain a moist environment.

There are two major types of subterranean ter-mites in South Carolina: several species of native

Basic Entomology X 142

Orthoptera: crickets, grasshop-pers, praying mantids (Figure 6.17)

-ten rather hard-bodied.

wings. Forewings are elongate, nar-row and hardened; hindwings are membranous with extensive folded area.

damaging.

mantids and walking sticks enlarged for jumping.

-ble adults but are wingless.

Thysanoptera: thrips (Figure 6.18)

and simple).

fringed with hairs.Flower thrips are tiny (1/16 inch long)

yellowish-brown to amber-colored insects that damage rose flowers by rasping the tissues and then sucking up the sap that oozes out. Their feeding causes flower buds to become streaked with brown discolored areas. Often the buds fail to open or the flowers look distorted. Thrips are especially fond of white or light-colored flowers. To check for thrips, open up a suspected flower over a sheet of white paper and look for tiny scurrying insects that resemble slivers of wood.

Thrips are difficult to control. Fortunately, they’re eaten by minute pirate bugs, ladybugs, lacewings, and big-eyed bugs. Remove and dis-card any infested flowers.

Common “Noninsects” A number of insect relatives belong to the

Phylum Arthropoda. They include spiders, ticks, and mites (Arachnida), pill bugs (Crusta-cea), millipedes (Diplopoda) , centipedes (Chi-

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Order Orthoptera Figure 6.17

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Order Odonata

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Figure 6.16

Basic Entomology X 143

Many mites are smaller than the period on this page and are best viewed with a magnifying glass. To inspect for mites, simply tap an affected leaf over a piece of white paper and look through the lens for tiny moving specks.

Eriophyid mites include rust, bud, and blister mites. They have four legs instead of the usual eight legs--a characteristic of most arachnids.

Spiders are larger than mites and have two body regions that are distinct from one another. There are 3,000 species of spiders that live in the U.S. Most are beneficial predators, and many spiders do not produce webs. Instead, they lie in wait for their prey. They feed on insects and other small animals by paralyzing them with venom.

Three dangerous spiders are commonly found in South Carolina, all widows. The Southern black widow is found throughout the state. It is easily identifiable by the shiny, black bulbous body with the abdomen bearing a red “hourglass” marking on its underside. The Southern black widow usually is found outdoors under stones, logs, or other dark protected areas in and around buildings.

The Northern black widow is found in the mountains and the Piedmont of South Carolina. The Northern black widow looks similar to the Southern black widow; however, it lacks the “hourglass” marking on the underside; it has two red mark spots instead.

The brown widow, extremely rare in South Carolina, is a widespread species found in tropi-cal areas. It was introduced into Florida and has expanded its range northward into South Carolina. In the late 1990s it had been reported in Charleston and Beaufort. Since the summer of 2002 more reports of its presence have been made in numerous areas of the state.

Brown widow spiders are gray to brown in color with white and black markings on the top surface of their bulbous abdomens. The “hour-glass” marking on the underside of the abdomen

is yellow to orange and the legs have dark bands.

All three widow spiders in South Carolina are shy and will try to flee rather than bite a human. Cases of widow bites occur when a spider is pressed against

lopoda). Snails and slugs in the Phylum Mollusca, are also found in the garden and landscape.

Arthropods lack the characteristic features of insects. Arachnids, for example, have two main body regions: a cephalothorax and an abdomen, eight legs, no antennae, and no wings.

Arachnids: mites, spiders, and ticks (Figure 6.19)Arachnids have no antennae, no wings, and two body

regions that not are clearly distinct from one another. Adults have four pairs of jointed legs while adult insects have six legs.

Spider mites are tiny, soft-bodied arachnids. They are common pests of many fruit and nut trees, vegetable crops, ornamentals, and houseplants. With their piercing mouthparts, spider mites suck plant sap from the under-sides of leaves causing the upper surfaces to turn bronze or yellow. Eventually the leaves may turn brown and fall off. Heavily infested leaves can be covered with webs.

Common species include southern red or “cool weather” mites which reproduce rapidly in spring and fall. Two-spotted spider mites (pale yellow, green, brown or red) have two spots on their backs; they become active during the heat of summer. Other common species are European red mites, which are red with white spines, and clover mites, which are reddish brown or gray and flat with very long front legs.

:WPKLY Mite ;PJR

Class Arachnida. Figure 6.19

0U�������WHY[Z�VM�:V\[O�*HYVSPUH�^PSS�L_WLYPLUJL�H�THQVY�LTLYNLUJL�VM����`LHY�WLYPVKPJHS�JPJHKHZ�(Magicicada tredecim����:PUJL�� ��[OL�`V\UN�JPJH�KHZ�OH]L�ILLU�ILSV^�NYV\UK�Z\JRPUN�ZHW�MYVT�YVV[Z�HUK�HYL�L_WLJ[LK�[V�LTLYNL�PU�SH[L�(WYPS�HUK�LHYS`�4H �̀�;OL����`LHY�JPJHKH�PZ�H�ZV\[OLYU�MVYT�^OPSL�[OL����`LHY�JPJHKH��M. septendecim��[LUKZ�[V�IL�H�UVY[OLYU�MVYT�

Figure 6.18

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Thysanoptera

Basic Entomology X 144

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Class Diplopoda. Figure 6.22

the skin of a person (for example, when putting on clothes or shoes) or when a hand is reached into dark areas where the spider is present. It has been reported that the venom of the brown widow is as toxic as the black widow spider, but they are less likely to bite and do not defend their webs as vigor-ously as black widows.

The brown recluse spider, extremely rare in South Carolina, is often confused with harmless wolf spiders and other hunting spiders. The spider is light brown or grayish with long, delicate legs. The “fiddle” or violin outline on the back is not a de-pendable character since many brown spiders have similar markings. It is about the size of a quarter (with legs) when mature. The primary key to iden-tification are the three pairs of eyes.

Ticks are external parasites of people and ani-mals. They need a blood meal to survive and repro-duce. Ticks can feed on humans and other mam-mals, reptiles, birds or even frogs. All life stages of ticks feed on blood. Ticks can transmit several dis-eases, such as Lyme disease, rocky mountain spotted fever, tick paralysis, and others, but most tick bites do not result in illness.

Chilopoda: Centipedes (Figure 6.20)Centipedes strongly resemble millipedes, except

that they have longer antennae, are more flattened in cross-section, and have only one pair of legs on

each body segment. They are beneficial predators of other arthropods. Centipedes are nocturnal and ac-tively seek dark shelter if exposed. The first pair of legs possess venom glands, which they use to subdue their prey.

Order Isopoda—Sowbugs and pillbugs (Figure 6.21)

Sowbugs and pillbugs look similar in appear-ance. They are gray, oval-shaped, and about 1/4 to 5/8 inch long. Their hard, rounded outer shell is composed of a number of plates.

Sowbugs have two taillike structures, unlike pill-bugs. Another difference between the two is that pillbugs or “roly-pollies” can roll up into a tight ball when disturbed; sowbugs cannot.

Sowbugs and pillbugs are active at night, mainly feeding on dead plant material and occasionally, young plants and their roots, often causing little injury.

They breathe with gill-like structures and must be in very moist areas to survive. Look for them during the day in moist areas, such as under rocks, boards, mulch, or leaf-litter. They do not bite and are completely harmless to humans.

Diplopoda—Millipedes (Figure 6.22)Millipedes are wormlike with two visible ana-

tomical regions: a head and body. They are gener-ally round in cross-section, and all but the first four or five body segments possess two pairs of legs. Mil-lipedes are generally inoffensive creatures that feed on fungus and decaying plant material. At times, they can be fairly destructive to vegetables or other plants in greenhouses.

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Class Chilopoda. Figure 6.20

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Order Isopoda. Figure 6.21

Basic Entomology X 145

Identifying InsectsEntomologists examine insects under a magnify-

ing lens, dissecting scope, or microscope and use ana-tomical features or body parts to distinguish, classify, and identify insects. Identifying insects to the species level is often difficult, and may require a key. There are field keys that help identify the insect based on plant damage, such as insects that mine or eat holes in the leaves as opposed to sap-sucking insects that cause discolored or deformed leaves. When an insect specimen is available, keys help identify the insect from orders down to the species level.

Identifying a given insect to the species level is often difficult. It may include counting the number of teeth on the mandibles or the number of segments on the antennae. Sometimes entomologists use the arrangement and length of hairs on the head, thorax or abdomen or the arrangement of veins in the wings as identifying characteristics.

:UHPSZ�HUK�ZS\NZ�HYL�ZTHSS�ZVM[�IVKPLK�HUPTHSZ�;OL`�HYL�UV[�HY[OYVWVKZ��I\[�[OL`�JHU�IL�[YV\ISLZVTL�WLZ[Z�PU�[OL�NHYKLU���;OL�IYV^U�NHYKLU�ZUHPS��Helix aspersa) HUK�[OL�NYH`�NHYKLU�ZS\N��Deroceras reticulatum) are HTVUN�[OL�TVZ[�IV[OLYZVTL�WLZ[Z�PU�:V\[O�*HYVSPUH���;OL`�HYL�]LY`�ZPTPSHY�[V�LHJO�V[OLY�L_JLW[�ZUHPSZ�OH]L�OHYK�ZOLSSZ�HUK�ZS\NZ�KV�UV[���;OL`�JHU�JH\ZL�ZLYPV\Z�KHTHNL�PU�[OL�NHYKLU��HUK�VM[LU�YLTHPU�\UZLLU��ZPUJL�[OL`�MLLK�H[�UPNO[�VY�VU�YHPU`�KH`Z��+\YPUN�[OL�KH`�[OL`�JHU�IL�MV\UK�OPKPUN�PU�KHTW�WSHJLZ�Z\JO�HZ�PU�[OPJR�NYV\UKJV]LYZ�VY�\UKLY�ÅV^LY�WV[Z���;OL�TVZ[�JOHYHJ[LY�PZ[PJ�ZPNUZ�VM�[OLPY�WYLZLUJL�HYL�[OL�[YHPSZ�VM�T\J\Z�[OL`�SLH]L�^OLYL]LY�[OL`�JYH^S�

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Credit: �*HSPMVYUPH�4HZ[LY�.HYKLULY�/HUKIVVR. 2002. Dennis R. Pittenger, ed. Univ. of Calif. Agric. and Natural Resources, Pub. 3382. Copyrighted by the Regents of the Univ. of California and used with permission.

Phylum Mollusca: Snails and slugs

For home gardeners, knowing the exact species of an insect may not be necessary, especially after you determined that it’s beneficial or harmful. If it’s a harmful pest, such as aphids, the exact species does not have to be determined. After all, the control measures for most aphids would be the same, regard-less of the species. The same could be said about mealybugs, most soft scales, spider mites, and many other common pests, provided that you identified the host plant.

Knowing the identity of the host plant is very important because it helps to reveal an insect’s iden-tity. Although some insect pests are general feeders that feed on a variety of different plants, many are quite host-specific. For example, the dogwood twig girdler only attacks dogwood. You will not find it feeding on pines, oaks, camellias, or other plants.

Knowing the identity of the host and pest is also important, when providing recommendations for chemical pesticides, particularly on vegetables, fruit, or other edible crops.

Basic Entomology X 146

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Basic Entomology X 147

Diagnosing Plant Problems Caused by Insects and Mites

Determining the cause of poor plant perfor-mance is a difficult task because Master Gardeners and other diagnosticians often have incomplete evidence. The diagnostic process involves gathering the facts from the Plant Problem Clinic Diagnostic form and from the person submitting the sample. Then you need to draw on your past experiences, published references, and other resources. Ideally, a diagnosis should include a site visit which yields more evidence to help with an accurate diagnosis. Unfortunately, visiting the location where the sam-ple was taken is often not possible. So, it’s impor-tant that when confronted by a problem, the Master Gardener follows these tips for diagnosing insect and mite-related problems:

determine the identity of the pest which results in successfully managing it. A majority of insects and mites have preferred host plants, while some are general feeders. Most of the references are orga-nized by host plants that are being attacked which will help you determine the insects that could be involved. Is the problem localized to one or several plants? Is it on a single species or several species of plant? What type of damage is occurring?

advice, it may be too late to take any corrective action in that particular growing season. In some situations, the pest may be gone and the damage re-mains. Become familiar with the pest’s life cycle to determine if there are subsequent generations that need to be controlled.

-mendation based on the client’s verbal description. Ideally, see the damage and the insect itself to avoid making an inaccurate identification. Use a hand lens, if necessary. Your client may have to resubmit digital images of the pest according to the guidelines listed in the box on the left. The incorrect iden-tification of an insect results in ineffective control measures, unnecessary expense, and potential harm to beneficial insects.

-sity. Make your diagnosis or give research-based rec-ommendations that have been verified by Clemson University specialists. Consult the resources at the end of this chapter.

Present all appropriate options--handpicking, bio-logical, chemical--to your clients and allow them to choose the best method or combination that best suits their needs.

in doubt, do not make a diagnosis. Refer to your county agent, specialist, or Plant Problem Clinic.

-able to other causes other than insects or mites, such as disease, improper cultural practices or condi-tions that include too much or too little water, poor drainage, low or high light levels, physical or chemi-cal injury, not adapted to the location, too high or too low temperatures, and excessive or deficient levels of nutrients.

Landscape Plant Problems,” for a broader perspec-tive on diagnosing plant problems. In addition, read the Master Gardener logs where questions and answers are recorded to familiarize yourself with the seasonal problems. Also, study known samples that have been identified by a county agent, specialist, or Plant Problem Clinic.

Basic Approaches for Successfully Managing Pest Insects

Identify the Problem. People have different tolerance levels regarding pest infestations. Some will be indifferent about the number of aphids on their shrub roses, while others who show roses may want to take action when aphids first appear.

In some cases when a problem is brought to a Master Gardener’s attention, it’s too late too take any action because the damage is already done. When orange-striped oakworms have defoliated oak trees in September, it’s too late to control the pest. Killing mature or pupating caterpillars to reduce the severity of next year’s infestation is not an environ-mentally sound approach. Besides, the oaks will shed any remaining leaves in the next few months, so control is not warranted this late in the season.

Solving an insect pest problem entails more thought and knowledge than just identifying the pest.

Select a Proper Management Strategy. Select one or a combination of appropriate methods that insure the safety of the people involved as well as the environment. If several methods are avail-

Basic Entomology X 148

able, suggest all that are reasonable and approved by Clemson University. Take into account proper timing of the application which coincides with the most vulnerable time in the life cycle of the insect. Then, allow your client to choose the approach that’s best for them.

Because of their toxic nature, special attention should be devoted to pesticides to ensure their prop-er use. Pesticides must be used in strict accordance with the label instructions. The ornamental or food crop must be listed on the label or referred to under a general heading such as lawns, shrubs, trees, or other ornamentals. Products may have identical ingredients and are sold by different manufacturers, but their formulations, pests controlled, and applica-tion sites may vary. The user is responsible for find-ing a product that is appropriate for the particular pest, plant, and site.

See Chapter 9 for information on pesticide formulations, labels and labelling, application equip-ment, sprayer calibration, storage and disposal, and environmental concerns.

Evaluate the Results. Evaluate the pest control results to avoid or effec-tively manage this pest problem in the future. It may mean planting squash

in early spring to escape squash vine borer or replac-ing Japanese euonymus (Euonymus japonicus) with more resistant species to avoid having to protect it from euonymus scale.

)LULÄ[Z�HUK�=HS\L�VM�InsectsInsects must be studied carefully to distinguish

the beneficial from the harmful. People have often gone to great trouble and expense to destroy insects, only to learn later that they were not only harmless but were actually saving crops by eating destructive insects.

Insects are beneficial to gardeners for the follow-ing reasons:

melons, squash, and many other vegetables, and many ornamental plants (chrysanthemums, irises, orchids, and yuccas) are pollinated by insects.

Figure 6.23

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Basic Entomology X 149

insects.

ways that they injure crop plants.

soil and promote its fertility by burrowing through-out the surface layer. Also, the dead bodies and droppings of insects serve as fertilizer.

-gers by devouring the bodies of dead animals and plants and by burying carcasses and dung.

These benefits from insects, although genu-ine, are insignificant compared with the good that insects do when fighting each other. There is no doubt that the greatest single factor in keeping plant-feeding insects from overwhelming the rest of the world is that they are fed upon by other insects (Figure 6.23). Insects that eat other insects fall into two main categories known as predators and para-sites.

Predators are insects (or other animals) that catch and devour other creatures called prey, usually killing and consuming them in a single meal. The prey is generally smaller and weaker than the preda-tor. They include spiders, praying mantids, lady beetles, and green lacewings.

Parasites are forms of living organisms that live on or in the bodies of living organisms (hosts) from which they get their food during at least one stage of their existence. The hosts are usually larger and stronger than the parasites and are not killed promptly but continue to live in close association with the parasite. Braconid wasps and Trichogramma wasps are parasites (also called parasitoids) that hatch from eggs inside or on another insect and eat the host as they grow.

Predators are typically very active and have long life cycles; parasites are often slower and tend to have very short life cycles.

Releasing beneficial insects into your landscape or garden may offer some benefit, but it is better to conserve the beneficial insects already there. Learn to distinguish between pests and beneficial insects in your garden and landscape. Avoid applying broad spectrum insecticides to plants that will harm bene-ficial insects if it looks as if they are keeping harmful insects to tolerable levels.

References and Further ReadingTechnical BooksBorror and Delong’s Introduction to the Study of Insects,

7th ed., 2005. Charles A. Triplehorn and Nor-man F. Johnson. Thomson Brooks/Cole, Bel-mont, CA.

Insects that Feed on Trees and Shrubs. 1991. W. T. Johnson and H. H. Lyon. Cornell University Press, Ithaca, NY.

Gardener-friendly BooksGarden Insects of North America: The Ultimate Guide

to Backyard Bugs. 2004. Whitney Cranshaw. Princeton University Press, Princeton, NJ.

The Handy Bug Answer BookTM. 1998. Gilbert Wald-

Insects and Gardens: In Pursuit of a Garden Ecology. 2001. Eric Grissell. Timber Press, Portland, OR.

Pests of the Garden and Small Farm; A Grower’s Guide to Using Less Pesticide. 2nd ed. 1998. Mary Lou-ise Flint, Univ. of Calif. Press, UC Division of Agric. and Natural Resources, Berkeley, CA.

Simon and Schuster’s Guide to Insects. 1981. Ross H. Arnett, Jr. and Richard L. Jacques, Jr. Simon and Schuster, New York.

InternetClemson Entomology (http://entweb.clemson.edu/

insectinfo/index.htm). Texas A&M Insect Photo Gallery (http://entowww.

tamu.edu/imagegallery/).

USDA-ARS Image Gallery(http://www.ars.usda.gov/is/graphics/photos/).

Basic Entomology X 150

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Basics of Entomology Review