Proceednnqs of the 7th Internatumal Workmg Conference an Stored-product Protection - Volume 2

Possibilities of biological control of stored food mites

Eva crkovc and Radek Fcjr'

Abstract

Control measures based on the natural relationship betweena predator and Its prey are "biological' methods. Biologicalcontrol of stored product rmtes IS the only control method sofar widely used m grain stores Brological control has beenelaborated and tested in practice. It can be used as apreventive measure m empty stores and to prevent orrepress nutes populations on gram or seed The predatorused was Cheyletus eruditus (Schrank) CProetumuua.,Cheyletulae ), which feeds on mites of the farmhesAcaridae and Glycyphagulae i Asturmaia ), chiefly onAcarus siro L., Tyrophagus putrescentiae (Schrank) andLepidoglyphus destructor (Schrank). These species ofmites are important pests of stored food and It IS thereforenecessary to control them The biological control on oilseedsIS more difficult than on gram because oilseeds are veryattractive to rmtes. They can multiply to millions per kg onthem. The effectiveness of biological control on oilseeds ISevaluated.

Introduction

Control measures based on the natural relationship betweena predator and its prey are' biologIcal' methods. Whereasgreenhouse plants are extensively protected agamstphytophagous arthropods by biological means. Biologicalcontrol of stored product mites IS the only control method sofar Widely used in gram stores. Biological control has beenelaborated and tested m practice agamst mites of storedgram and seed The predator used was Cheyletus erudiius(Schrank) (Prostigmata: Cheyletidae), which feeds onmites of the families Acarulae and Glycyphagulae(Astigmata ), chiefly on Acarus siro L., Tyrophaguspuiresceniuie (Schrank) and Lepuloglyphus destructor(Schrank) .

1 Research Instltute of Crop Protection, Department of StoredProduct Pest Control Dmovska 507, 161 06 Prague 6, CzechRepublic

* Supported by the grant no 522/97/0334 of the Grant Agency of theCzech Republic

Acaroid mites

These species of rmtes are Important pests of stored food,both of plant and ammal ongm Their presence reduces themarket value of the food. They are a major pest of seedsEmbryos are attacked and this reduces the viability of seedstocks. MIte damage can also accelerate enzymatic activity,thus causmg rapid decomposition of seeds. MItes transmitpathogemc bactena and fungi. They are a hygienic problemas contammants of food for human and domestic animals. Ascomponents of house dust they cause dermatitis and variousallergies

The predator

The predator IS approximately 0.5 mm long, WIth two largepedipalps m front of the body. It reproducesparthenogenetically, 1 e. WIthout males. Females lay therreggs m cluster and guard them until the young are hatched.All developmental stages are predators and thus they do notdamage stored products The predatory mites can also becanmbahstic (they feed on specimens of their own species),when there IS a lack of other food. The predatory nutes cancomplete their life cycle at 12 - 35°C and 60 - 90% R H.The higher the temperature and the humidity, the fastertheir development. The shortest life cycle IS about 14 days.They are resistant to low temperature. At 0 ± rc they cansurvive for 3 - 6 months. The predatory mites are lesssusceptible to organophosphates than acaroid mites.(zdarkova, 1994) This IS very Important for combinationof chemical and biological control or when biological controlfollows the chemical application

History

The first one who pomted out the value of Cheyletus speciesfor controllmg mite pests of stored gram was Ewmg (1912).He descnbed the hfe history and habits of Cheyletusserninworus Packard and exammed a sample of mIlled wheatmfested WIth mIllions of mItes whIch were destroyed manlya few days by the predaceous mItesOver fIfty years later Pulpan and Verner (1965) proved

for the fIrst time that bIOlogIcal control of stored food mItesusmg the predator C. erud~tus actually worked m grainstores. They also determmed under WhICh conditions. C

1243

Proceedmqe of the 7th Internaiumal Worhng Conference on Stored-product Protection - 1lolume 2

eruditus may be introduced at any time of the year providedthe pest mites are present but not already approachmg theabundance level that would make fumigation necessary. Inwinter the gram IS too cold for Cheuletus to be active.However, some predators will survrve to reproduce m thespnng. If gram is mechanically cleaned on the conveyors, Itis necessary to remtroduce the predators, as they are usuallyelimmated WIth the dust and other debris, because they hveoutside the gram seeds. The authors recommended that thepredatory mites can be collected from gram stores, wherethe biological control had been completed. The authorssuggested to look for those reservoirs, sieve the predatorsout of the gram and use them for application as biologicalcontrol agents in other premises.However in spite of that biological control had not been

used on a large scale one, of the mam objections was thelack of predators when they were needed The Idea ofPulpdn and Verner was good, but the method was labonousand time consummg. When the reservoir of predators wasfound but there was no Immediate use for them, the effortwas m vain. Therefore zd6rkova and Pulpdn (1973) testedsurvival of the predators at temperatures ranging from-1.7 to + 2.0"C and relative hurmdities of 80 - 90%. Thebest results were obtained at + 2. O"C. Fifty percent ofpopulation of the predatory rrutes survived for 62 days, and8% for 200 days Without losing their ability to reproducewhen transferred back to favourable conditions. Populationsobtained from natural reservoirs and preserved under lowtemperatures could thus be used for biological control.However, it became clear that the technology of massrearing of the predators had to be developed in order to usethe method of biological control on a large scale.zd6rkova (1986) developed such a technique using A.

srro as the food for C. eruditus. The mam goal was toobtam as many predators as possible m the shortest period oftime, but the final population of predators should not containAcarus specunens. The predators are sold m paper bags(each containing 2000 - 3000 hve specimens of C.erudiius) under the commercial name CHEYLETIN.

Use of Biological Control

Preventive application in empty stores

One cause of infestation of stored food matenals by rrutesIS insufficient cleaning of empty stores. Particles of gramand other residues provide food and shelter for the storedfood mites. The disinfestation of empty stores IS veryImportant for post-harvest protection. If this IS not done,the residual pest population surviving in the stores from theprevious season Infests the freshly loaded gram. Chemicaltreatment, especially the synthetic pyrethroids, IS notcompletely adequate for controlling rrutes. Pesticides do notpenetrate all small cracks and crevices of the floor, where

the mites may fmd a shelter. Therefore a biological agent ISrecommended The predatory mites actively seek their preyand in addition, have a natural resistance against acaricides.Their release III the store is more convenient, moreeffective and less expensive than other control measures.The predatory rrutes should be released m the store,distributmg the contents of one bag evenly over an area of100 m2• HIgher effectiveness IS achieved If the store ismechanically cleaned before application of CHEYLETIN.The predator can be applied withm a week after chemicaltreatment.

Preventive application on grain and seed

Ten predators per 100 kg of gram or seed can be appliedas a preventive measure If the moisture of the storedmaterial is higher than 14% and the Infestation by mites ISvery probable; if the matenal Will be stored for at leastthree months and If the material IS not infested by any otherpests such as moths or beetles. The predators are spilledevenly on the grain and seed.

Repressive application on grain and seed

The first step is to find the mites m the gram and seed.Sampling should be made on different places of the pile ofgrain or on the top and outlet of silo bms or from bags. Froman area of 20 x 20 m, about 10 samples should be taken: 5from the surface, 5 from a depth of 0.5 - 1.0 m. Samplesare usually taken on SIdes and from the centre. In case ofbagged matenal samples should preferably be taken frombags adjacent to the walls or on the floor. The weight of onesample should be 100 - 200 g of seed and 2000 g of grain.Optimal conditions for using predatory mites for

repression are:- No pest species other than mites should be present m thestored matenals.

- Gram and seeds Will be stored for at least three months.- The temperature of the stored material IS higher than12"C .

- The infestation by mites does not exceed 1000 mites/kgof stored matenal. (HIgher population density of the pestmites disturbs nestmg females of Cheyletus. ).The predator-prey ratio should be 1 10 - 1 100,

dependmg on the moisture content of grain and seeds. If themoisture IS high, i e. m grain 16% or more, the acaroidmites develop fast and the ratio has to be low (1 10). If themoisture is rather low (13 - 14%), the ratio can be higher(l 100).SItes from whtch samples are taken from a pile of gram or

stlo bms should be marked With a wooden stick. Predatorsare distributed around the marked sites in the necessaryamounts. Application on bagged material is morecomplicated. Predators can be applied on the surface of bagsIf the bags touch upon each other and if the bag is

1244

Proceedings of the 7th International Working Conference on Stored-product Protecium. - Volume 2

sufficiently course to permit entry of the predators.Otherwise the bags must be opened or any other methods canbe used to allow the mites access to the seed (e. g. PIpe) Acheck at the release site should be made 4 - 6 weeks later.Biologtcal control IS successful If the number of predatorsnses and the number of pests drops. Subsequent samplmgcan be made once each month until the end of biologicalcontrol, 1 e. when only predators are present. This mayrequire 3 - 6 months, dependmg on the climatic conditions

Combination of chemical and biological control

When the infestation of acaroid mites IS higher than 1000specimens per kg of rnatenal or when other msect pests arealso present, It IS necessary to suppress the population ofmites (msects ) chemically. EIther fumigation or contactinsecticide can be used After the treatment a new samplmghas to be done, because the mortahty of the pest rrutes maynot be 100%. Predatory mites can be apphed as early as oneweek after chemical treatment

Biological control is completed

and dead mites, therr skms and fragments are present mthe matenal and before the gram IS used for humanconsumption these particles have to be SIeved or washedaway usmg common cleanmg procedures.

Biological control on oilseeds

Biological control have been successfully apphed on gramsuch as wheat and barley and on different seeds such asclover seed, cabbage seed, lettuce seed etc However, thyare not too many results concermng application of biologicalcontrol on oilseeds such as sunflower seeds, hnseeds andrape seeds. Oilseeds are very attractive to rrutes, on whichthey can multiply to milhons per kg. The 011seeds aretherefore very often chemIcally treated MItes are lesssenSItive to msectIcldes than msects. Pest control operators

solve this problem by mcreasmg the doses of conventionalmsecticrdes. MItes respond by raismg their resistance. ThISunwanted competition results m high residual level ofpesticides m oilseeds and therefore in 011 which goes toconsumers. Biological control can be a solution of thissrtuation It was necessary to fmd out If the predatory mitescan be an efficient agent also on oilseeds. By theexpenments which were done at the department of StoredProduct Pest Control, It became clear that biological controlon oilseeds also works The predator-prey ratio should be 110 - 1 50. dependmg on the mfestation of acaroid mites. Ifthe infestation IS low up to 500 specimens per kg, the ratiocan be higher (1 50 ), when the mfesta tion IS high up to1000 specimens per kg, the ratio should be rather low.Emphasis should be laid on prevention rather than onrepression m oilseeds

References

Ewing, H E (1912) The hfe-lustory and habits ofCheyletus seminicorus Packard. J Econ. Entomol , 5,416.Pulpdn, J. and Verner .P. H 1965. Control of tyroglyphoidrrutes m stored gram by the predatory mite Cheyletuseruditus (Schr; ) Can. J. Zool. 43 417-432.zddrkovu, E. 1986 Mass reanng of the predator Cheyletuseruditus for biological control of acaroid mites mfestmgstored products. Crop Prot. 5 122 - 124zdCirkova, E 1994. The effectiveness of organophosphateacancides on stored product mites mteractmg m biologicalcontrol. Experiment & Appl Acarol , 18. 747 -751zdCirkova, E. and Pulpdn, J. 1973. Low temperaturestorage of the predatory nute Cheyletus eruditus forfuture use in biological control. J. stored Prod. Res.9 217-220

1245