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Natural Enemies of Gypsy Moth:The GoodGuys!

“Natural enemies” refers to the predators, parasitoidsand pathogens that affect pest insects such as the gypsymoth (Lymantria dispar L.). These natural enemies areimportant in helping to control gypsy moth outbreaksand in keeping populations low in the years betweenoutbreaks. One reason why gypsy moth is a muchgreater problem in North America than in its nativelands is that many of its important natural enemies wereleft behind when gypsy moth became established here.

Some natural enemies of gypsy moth will be familiar toyou; others, such as insect parasitoids and pathogens,may be less well known. They all play important roles,however, in helping to limit the damage and annoyancecaused by gypsy moth. Some of the natural enemies thataffect gypsy moth are native to North America. Otherswere deliberately introduced from Europe, Asia, Indiaand northern Africa, where gypsy moth is native, by fed-eral agencies involved in biological control programs.

The goal of this bulletin is to help you learn to recognizesome of the important natural enemies that may helpcontrol gypsy moth in your area. This bulletin will alsogive you suggestions on tactics to conserve or protectnatural enemies of gypsy moth on your property.

PredatorsPredators of gypsy moth are important in keeping gypsymoth populations low in years between outbreaks. Adiverse group of bird, mammal, amphibian and insectpredators will feed on gypsy moth eggs, caterpillars andpupae. Woodlots, urban forests and landscapes thatinclude a diverse mix of forest trees, shrubs and herba-ceous vegetation will provide cover and other resourcesfor predators. Restrict use of broad-spectrum insecticidesto avoid harm to populations of predatory insects. Themicrobial insecticide known as B.t. or B.t.k. (Bacillusthuringiensis var. kurstaki) is often used to protect treefoliage in residential areas during gypsy moth outbreaks.Unlike conventional insecticides, B.t.k. will not harm ver-tebrate or insect predators.

Extension Bulletin E-2700, April 1999 (New)

Michigan State University Extension

Dr. Deborah G. McCullough Dr. Kenneth A. Raffa Dr. R. Chris WilliamsonAssociate Professor Professor Extension Entomologist

Dept. of Entomology and Dept. of Forestry Dept. of Entomology Dept. of EntomologyMichigan State University University of Wisconsin-Madison University of Wisconsin-Madison

BirdsMany birds do not like to feed on large, hairy gypsymoth caterpillars, but other species seem to relish them!Yellow-billed and black-billed cuckoos, blue jays, oriolesand rufous-sided towhees are among the species thatfeed on gypsy moth caterpillars. Some birds, such as theblack-capped chickadee, will also feed on egg massesand can sometimes cause substantial egg mortality.

MammalsShrews, mice, voles and other small mammals often feedon gypsy moth caterpillars and pupae that theyencounter on the ground and around the bases of trees.Mice (Fig. 1) seem to prefer the large female pupae to thesmaller male pupae. This selective feeding can have agreater impact on the overall gypsy moth populationthan random feeding. Chipmunks, skunks and racoonswill also feed on gypsy moth larvae and pupae, andsquirrels will feed on pupae.

Fig. 1. Mice are important predators of gypsy moth caterpillarsand pupae.

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Natural Enemies of Gypsy Moth: The Good Guys!

Insect predatorsSome insects are alsoimportant predators ofgypsy moth. For exam-ple, the Calosoma beetle(Calosoma sycophanta) is a“specialist,” in that itfeeds almost entirely ongypsy moth (Fig. 2). Itwas introduced into thenortheastern UnitedStates and, more recent-ly, into Michigan in theGreat Lakes region,specifically to help pro-vide long-term control ofgypsy moth populations.Adults and larval stagesof this brightly coloredbeetle feed on gypsymoth caterpillars andpupae (Fig. 3).

Several native insects arealso good predators andwill attack gypsy moth,as well as other plant-feeding insects. Forexample, in Fig. 4, apredatory stinkbug isfeeding on a gypsy mothcaterpillar. Ants can alsobe important predatorsof young caterpillars.Many other insect preda-tors and spiders areopportunistic feedersand will consume gypsymoth larvae or pupaewhen they are available.

ParasitoidsThe term “parasitoid” refers to certain species of waspsand flies that have a very specialized life cycle.Parasitoids lay their eggs inside, on or near the body of ahost insect, such as a gypsy moth caterpillar (Fig. 5). Thelarval stages of most parasitoids resemble maggots.Parasitoid larvae live by feeding on tissues in the body of

the host insect,killing it in theprocess. Once theparasitoid has com-pleted its develop-ment, it emergesfrom the host insect.Several parasitoidsare important natur-al enemies of gypsymoth. A few exam-ples are describedhere.

Ooencyrtus kuvanaeThis little wasp is a specialist that parasitizes the eggs ofgypsy moth (Fig. 6). It was introduced into the UnitedStates for biological control of gypsy moth many yearsago and is now well established in most of the regioninfested by gypsy moth. Three generations of this waspmay occur in the summer and fall after egg masses arelaid, and another generation may occur the followingspring. The tiny, dark adult wasps can often be observedif you look closely at gypsy moth egg masses. You mayalso see the small, round holes in the egg mass where theadult wasps emerged (Fig. 7). Because the wasp is small,it can usually attack only the eggs in the upper layer of agypsy moth egg mass. In many years, however, it is ableto kill 20 to 30 percent of the eggs in an egg mass.

Fig. 2. The adult Calosoma syco-phanta beetle is a gypsy mothpredator.

Fig. 3. Calosoma beetles willclimb trees to prey on gypsy mothlarvae.

Fig. 4. A predatory stinkbug attacks a gypsy moth caterpillar.Photo by Lyle Buss.

Fig. 5. A parasitoid fly laid the white egg on this gypsy mothcaterpillar. Photo by Ron Weseloh.

Fig. 6. Ooencyrtuskuvanae is an importantegg parasitoid of gypsymoth. Photo by MichaelHiggins.

Fig. 7. Holes in a gypsy moth eggmass where Ooencyrtus kuvanaewasps emerged after parasitizinggypsy moth eggs. Photo byMichael Higgins.

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Natural Enemies of Gypsy Moth: The Good Guys!

Although Ooencyrtus wasps are rarely available fromcommercial suppliers, you can help to protect popula-tions that are established in your area. For example, ifyou intend to scrape off and destroy egg masses as partof your gypsy moth management program, it is best towait until winter. This will give the egg parasitoids achance to complete their development and find over-wintering sites in the litter below trees. Limit use ofinsecticides in mid- and late summer to avoid killing thisbeneficial species. The microbial insecticide B.t.k. willnot harm parasitic wasps or flies.

Cotesia melanoscelusThis is another spe-cialized wasp thatwas introducedspecifically for bio-logical control ofgypsy moth. Thefirst generation ofthe wasp will attackvery young gypsymoth caterpillars(Fig. 8) and is oftensuccessful in subdu-ing the young hostcaterpillar. A sec-ond generation ofthe wasp can attacklarger gypsy mothcaterpillars, thosethat are about

halfway throughtheir development.

This parasitoid pupates in asmall, oblong yellowishcocoon (Fig. 9). Thesecocoons are frequentlyobserved near a dead gypsymoth caterpillar or attachedto the bark of an infestedtree. In some cases, this para-sitoid can be an importantsource of mortality.However, the small waspssometimes have difficultyattacking larger gypsy mothcaterpillars, and the wasp hasits own natural enemies thatmay limit its effectiveness.

Avoiding applications of broad-spectrum chemical insec-ticides in early and midsummer will help protect thisspecies. Application of the microbial insecticide B.t.k.may slow the development of gypsy moth caterpillars.This can benefit the Cotesia melanoscelus wasps and mayincrease the rate of parasitism. If you use burlap “hidingbands” on your trees and then mechanically remove

gypsy moth caterpillars (Fig. 10), you should avoidremoving any caterpillars with the yellow or whiteCotesia melanoscelus cocoons still attached (Fig. 11).

Compsilura coccinnataThis fly attacks gypsy moth caterpillars, as well as thecaterpillars of more than 100 other moth and butterflyspecies. It was introduced for gypsy moth control manyyears ago and is well established throughout much of thenortheastern and north central United States. It has three

generations a year,although only one ofthese generations attacksgypsy moth caterpillars.After feeding in the bodyof a gypsy moth caterpil-lar, this parasitoidpupates in a reddishbrown puparium, oftenseen on or near the bodyof the dead caterpillar(Fig. 12). This parasitoidmay be important inhelping to keep gypsymoth populations incheck and prolonging theperiod between out-breaks.

Fig. 9. A white Cotesiamelanoscelus cocoon nearparasitized gypsy mothcaterpillars.

Fig. 8. A Cotesia melanoscelus waspparasitizes a young gypsy moth cater-pillar.

Fig. 10. Gypsy moth caterpillars hide under burlap bands andcan be removed. Photo by Lyle Buss.

Fig. 11. This gypsy mothcadaver with the whiteCotesia melanosceluscocoon should be left onthe burlap band to allowthe parasitoid wasp toemerge.Photo by Lyle Buss.

Fig. 12. The reddish brown puparium indicates that this gypsymoth caterpillar was killed by aparasitic fly such as Compsiluracoccinnata. Photo by Lyle Buss.

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MSU is an Affirmative-Action/Equal-Opportunity Institution. Extension programs and materials are available to all without regard to race, color, national origin, sex, dis-ability, age or religion. n Issued in furtherance of Extension work in agriculture and home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S.Department of Agriculture. Arlen Leholm, extension director, Michigan State University, E. Lansing, MI 48824. n This information is for educational purposes only.References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This bulletin becomes publicproperty upon publication and may be printed verbatim with credit to MSU. Reprinting cannot be used to endorse or advertise a commercial product or company.

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PathogensGypsy moth and other insects are affected by a variety oforganisms that cause disease, including fungi, bacteria,viruses and protozoans. Two diseases are especiallyimportant in controlling gypsy moth outbreaks.

NPV - The Virus DiseaseNPV is a nucleopolyhedrosis virus, and is a disease thataffects only gypsy moth. The NPV disease is usually themost important factor in the collapse of gypsy moth out-breaks in North America. The virus is always present ina gypsy moth population and can be transmitted fromthe female moth to her offspring. It spreads naturallythrough the gypsy moth population, especially whencaterpillars are abundant. During a gypsy moth out-break, caterpillars become more susceptible to this virusdisease because they are stressed from competing withone another for food and space. Typically, 1 to 2 yearsafter an outbreak begins, the NPV disease causes a majordie-off of caterpillars.

Caterpillars killed by the NPV disease hang in an upside-down V shape from trees (Fig. 13). The bodies of thedead caterpillars liquefy (Fig. 14) and rapidly disinte-grate. A limited amount of the gypsy moth NPV diseaseis produced annually and distributed by the state andfederal agencies that oversee gypsy moth suppressionprograms.

Entomophaga maimaiga - The Fungus DiseaseThis fungus has recently attracted much interest in thenortheastern and north central states. It was introducedfrom Japan in 1910 but did not affect gypsy moth popu-lations until the late 1980s. What happened to the fun-gus in the years between its introduction and 1988-89 is amystery. Since 1989, the fungus has been widelyreleased in states with gypsy moth populations.

Fungal spores that overwinter in the soil will infectyoung caterpillars early in the summer. When the youngcaterpillars die, their bodies produce windblown spores(Fig. 15) that can spread and infect older caterpillars.Large caterpillars killed by the fungus will hang head-down from the tree trunk, and the bodies of the deadcaterpillars (cadavers) appear dry, stiff and brittle (Fig. 16). Within several days, the cadavers fall to thesoil and disintegrate, releasing the spores that will over-winter back into the soil.

Like all fungi, Entomophagamaimaiga is strongly affectedby temperature and mois-ture. Cool, rainy weather inthe spring and early summerprobably favors the fungus,but the specific conditionsneeded for good control arenot yet known. When condi-tions are right, however, it

can be an important source of mortality in both low andhigh gypsy moth populations.

MICHIGAN STATEU N I V E R S I T Y

EXTENSION

Natural Enemies of Gypsy Moth: The Good Guys!

Fig. 14. Caterpillars killed bythe NPV pathogen liquefyrapidly.

Fig. 15. Spores of theEntomophaga maimaiga fungus on a gypsy moth cater-pillar. Photo by Darwin Dale.

Fig. 16. Gypsy moth caterpillarskilled by the Entomophagamaimaiga fungus hang from thetree and are dry and brittle.Photo by Lyle Buss.

Fig. 13. Gypsy moth caterpil-lars that die from the NPV dis-ease hang from trees in anupside-down V shape.