TECHNOLOGY 

TRANSFER

Bioinsecticide

U.S. Department of Agriculture

FHAAST-2017-01

March 2017

Forest Health Assessment 

& Applied Sciences Team

Forest Service

John D. Podgwaite

Richard C. Reardon

Vincent D’Amico

Roger T. Zerillo

A Role for Ground-based Gypchek Treatments

for Gypsy Moth Control
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technologies to protect and improve the health of American forests. FHTET became Forest Health 

Assessment and Applied Science Team (FHAAST) in 2016. This booklet was published by FHAAST 

as part of the technology transfer series.

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A Role for Ground-based Gypchek Treatments

for Gypsy Moth Control

John D. Podgwaite1

Richard C. Reardon2

Vincent D’Amico3

Roger T. Zerillo1

For additional copies of this publication or information concerning Gypchek, contact either

Dr. John Podgwaite in Hamden, CT at (203) 230-4325, Dr. Richard Reardon in Morgantown, WV 

at (304) 285-1566, Dr. Steven Covell, in Arlington, VA at (703) 605-5342, or your local Cooperative 

Extension Service office.

1 USDA, Forest Service, Northern Research Station, Hamden, Connecticut

2 USDA Forest Service, Forest Health Assessment and Applied Sciences Team, Morgantown, West Virginia

3

 USDA Forest Service, Northern Research Station, Department of Entomology and Wildlife Biology, University 

of Delaware, Newark, Delaware

Acknowledgements

The authors wish to thank Nathan Havill (NRS-Hamden, CT) and Lee Solter (Illinois National History Survey, Urbana, IL) 

for reviewing earlier drafts of the manuscript

Ground-based Gypchek Treatments for Gypsy Moth Control

1

Introduction

The gypsy moth-specific baculovirus (LdMNPV) product Gypchek was developed by the USDA Forest Service as an alternative to the use of broad-spectrum insecticides for gypsy moth control. Registration of Gypchek as a general use insecticide has provided resource managers with a safe choice for the treatment of infestations where environmental issues, such 

as the presence of an endangered or threatened species, are of concern (Podgwaite 1999, Reardon et al. 2016). The product 

is most often aerially-applied to forested areas, either by fixed- or rotary-wing aircraft, and is effective in protecting foliage 

and reducing larval populations in the year of treatment and the following year (Podgwaite et al. 1992a, 1992b). Aerial applications are conducted under the auspices of gypsy moth management programs that are funded and facilitated through 

the Federal and State Gypsy Moth Cooperative Suppression and Eradication Program. At present Gypchek is produced for 

the Forest Service by Sylvar Technologies, Inc., a Canadian company. Production is fixed at 8,400 acre treatments per year. 

Here we briefly review and discuss the research that has been conducted on ground-based Gypchek applications and offer 

justification for their use. 

History of LdMNPV

Late in the 19th Century it became clear to European entomologists studying the gypsy moth 

(Lymantria dispar) that a disease was responsible for dramatic collapses of populations of the 

pest (Porchinsky, 1904). The disease, often referred to as “Wilt” due to the flaccid nature of 

dead larvae (Figure 1), was not observed in the United States until the early 1900’s. At that 

time researchers speculated that the causative agent was a “polyhedral body” associated with 

the dead larvae, but there was not a clear understanding of the pathological processes involved 

nor knowledge of the epizootiology of the disease. There were no reports of virus-killed larvae 

oozing their contents directly onto egg masses or of female moths depositing eggs onto virus 

contaminated bark (Figure 2). Although remains of dead larvae were observed on foliage, the 

early literature shows no evidence of that specific knowledge being useful, except in speculating 

that the virus itself might in some way be used to control gypsy moth (Reiff, 1911). Ultimately, 

with the advent of high-resolution microscopy and advanced bioassay technology, the disease 

was shown to be caused by a baculovirus (nucleopolyhedrovirus) and also that it was associated 

with gypsy moth eggs (Bergold, 1947). Subsequently, the virus was shown to passively contaminate eggs through contact with contaminated bark or leaves in the pest’s habitat and by the female moth during oviposition 

(Doane, 1969, 1975). More recently the virus has been shown to be covertly present within the egg, passed there by the female 

moth and moved to the next generation by transmission mechanisms that are yet to be completely understood (Il’inykh et al., 

2004). 

Egg mass treatments in Russia, Ukraine, Germany and Canada

Exactly when virus-contaminated (sprayed) egg masses were first used to 

manage gypsy moth is not clear, but several field experiments were reported 

in the Russian and Ukrainian literature beginning 

in the early 1960’s. Much of this is work is reviewed 

by Orlovskaya (1970) and abstracts of many studies 

can be found in Baranchikov et al. (1998). Most of 

the reported field experiments involved the topical 

treatment of individual egg masses within “foci” of 

gypsy moth infestations, either in forests or in fruit 

orchards. The expected results were that the virus 

would not only reduce larval populations within the 

foci but also spread from these foci and lead to viral 

epizootics, or at least some reduction in gypsy moth 

population density in nearby areas in the following 

year. Typically, a variable number of egg masses 

were misted with a hand-held sprayer containing a 

Figure 1. Gypsy moth larva 

killed by Gypchek.

Figure 2. Scanning electron micrograph of viral occlusion bodies (arrow) 

on the bark (Kathleen Shields). Gypsy moth female depositing an egg 

mass on virus-contaminated bark (Roger Zerillo). 

→
Ground-based Gypchek Treatments for Gypsy Moth Control

2

known volume and concentration of the Russian commercial 

preparation of baculovirus 

(Virin-ENSh). Larval mortality 

was assessed relative to that 

occurring in untreated control 

areas. Results of some studies 

indicated that treatments were 

efficacious in significantly reducing larval populations, not 

only in the area of treatment 

but also throughout the infestation foci in the years following treatment (Yatsenko and 

Rudnev, 1989). Results of other 

studies, although showing positive results in the vicinity of egg mass treatments, were less convincing regarding effectiveness in spreading the virus disease 

to areas distant from the treatments (Agafonova et al., 1978). Notwithstanding the ambiguity in some of the field experiments, 

egg mass treatments with Virin-ENSh became a useful approach to managing gypsy moth infestations on small plots in Russia 

while aerial treatments were preferred for infestations on large tracts. It should be noted that the Russian virus product has 

not been available for use outside of government-sponsored programs, principally because over 99% of gypsy moth infested 

forested-lands in Russia are under government control (V.V. Martemyanov, personal communication). Likewise, Gypchek is 

not available for use outside of government-sponsored programs in the US, but for different reasons.

Gypsy moth is not a major pest in Germany. However, a serious infestation occurred in 1984-85 prompting German 

scientists to introduce LdMNPV into an infested forest (Bogenschutz, et al. 1989). Following successful laboratory tests 

with Gypchek supplied by the U.S. Forest Service sprayed on field-collected egg masses, egg masses in an oak stand were 

sprayed. The researchers calculated that virus mortality, shown by DNA analysis to be due to Gypchek, would have reached 

95 % if not for concurrent mortality caused by parasitoids. The results of laboratory and field tests in Canada by Cardinal 

and Smirnoff (1973) led those authors to conclude that egg mass treatments would have a good chance of establishing 

viral epizootics and of reducing pest populations to enzootic levels. Also, the results from Lavigne and Carter (1996), who 

treated egg masses in three sites in New Brunswick, Canada, showed post-treatment egg mass reductions of 17, 24 and 65% 

in the three sites. The authors suggested that the technique had the potential for controlling gypsy moth in small isolated 

infestations. Other Canadian scientists treated egg masses in three urban Toronto parks and observed two waves of 

LdMNPV mortality in treated sites but not in untreated control sites. The result strongly suggested that virus-infected larvae emerging from egg masses were responsible for initiating the second wave of larval mortality. Unfortunately, significant 

larval mortality from the fungal pathogen Entomophaga maimaiga in the following year prevented an accurate assessment 

of any long-term impact the egg mass treatments may have had on gypsy moth population dynamics in the area (Thurston 

and Lapointe, 2008).

Egg mass treatments in the United States

Though there are only a few published studies on field treatments of 

gypsy moth egg masses in the United States, there are unpublished 

laboratory and field data supporting the potential of this treatment 

method. Campbell (1983) tested egg mass treatments separately and 

in combination with several other control measures in small forest 

plots in Eastford, CT and Lisbon, NJ. In general, there were no significant differences between the egg mass treatments and untreated 

control plots in reducing populations or protecting foliage. However, 

the lack of treatment effect was most likely due to the low potency 

of the virus suspension used in the field. The survival rate of larvae 

emerging from eggs treated with the same suspension in the laboratory was quite high (74%) compared with 95% survival larvae emerging 

Figure 3. Topical treatment of egg masses with hand-held, pump-up hydraulic sprayer. (Roger 

Zerillo)

Figure 4. Gypsy moth larvae emerging from an egg 

mass. Nearly 90% or the first instar will die when the 

egg mass is treated with Gypchek. (Roger Zerillo)
Ground-based Gypchek Treatments for Gypsy Moth Control

3

from un-treated egg masses. Podgwaite et al. (1981) treated egg masses in two forest plots in Connecticut with a concentrated suspension of viral occlusion bodies (OBs) using hand-held pump-up sprayers (Figure 3) to test the feasibility of 

integrating virus introduction with small mammal management for control of the gypsy moth. Unfortunately, an area-wide 

gypsy moth population collapse in the second year of the study made it impossible to evaluate efficacy of the combined 

tactics; however, treated egg masses brought back to the laboratory in both years showed 87% mortality in emerging larvae 

(Figure 4) and indicated that egg mass treatments most likely would have value where populations were not likely to be 

overwhelmed by naturally occurring disease. An effective tank-mix for the treatment of individual egg masses is shown in 

Table 1.

Table 1. Gypchek tank mix for application directly to egg masses1

Ingredient Amount per 3.79 liters (1 gal)

Tween 80 (polysorbate 80)2 1.5 ml (0.5 fl oz) (0.04% v/v)

Nonchlorinated water 3.78 liters (~1 gal) (99%)

Gypchek 378 billion OBs 1

 Soak egg masses with about 1 fl. oz. of tank mix just prior to hatch

2

 Wetter/spreader (many commercial sources, e.g., Lowes, Walmart, Amazon.com)

Broadcast treatment of egg masses with manual backpack sprayers (Figure 5) or ground-based hydraulic sprayers (Figure 

6) does not appear to offer the same degree of efficacy as observed from the topical treatment of individual egg masses. In 

1983 backpack mist-blower applications of concentrated suspensions of Gypchek to low and moderate egg mass-density 

populations in West Virginia woodlots resulted in no statistically significant changes in egg-mass densities in the following year. However, the trend in egg density (post treatment/pretreatment) was lower in the moderate density treated plots 

(1.90) than in moderate density untreated control plots (5.34) (Podgwaite, unpublished data). In Maryland in 1985, prior 

to gypsy moth egg hatch, four small woodlots were treated with Gypchek using ground-based hydraulic equipment. The 

following year, egg mass density decreased in three of four treated plots but increased in three of four untreated control 

plots (Podgwaite, unpublished data). In Massachusetts in the spring of 1991, prior to gypsy moth oviposition, the boles of 

trees in seven 400 m2 forest plots were treated with Gypchek using a backpack mistblower. In 1992, viral mortality of larvae 

emerging from egg masses collected from these sites was compared that of larvae from egg masses collected from untreated 

sites. Mortality due to 

virus was significantly 

higher in larvae emerging from eggs collected 

from the treated sites, 

but subsequent weekly collections of larvae 

from both treated and 

untreated sites showed 

no significant differences 

in mortality caused by 

LdMNPV. The authors 

speculated that the lack 

of treatment effect may 

have been caused by 

infected first-stage larvae 

ballooning from treated 

plots into control plots 

(D’Amico, et al., unpubFigure 5. (left) Backpack mist blower treatment of Gypchek to egg masses. (Roger Zerillo) Figure 6. 

(right) Ground-based hydraulic treatment of Gypchek to egg masses. (Roger Zerillo)
Ground-based Gypchek Treatments for Gypsy Moth Control

4

lished report). 

Larval treatments in the United States

Four major field experiments conducted between 1986 and 1997 

demonstrated the efficacy of Gypchek against gypsy moth larval 

populations when they were treated using ground-based hydraulic 

equipment. The first treatment was application to trees (Figure 7) in 

homeowner-sized lots in Maryland that resulted in an average of 80% 

viral mortality in larvae collected after treatment and reared in the 

laboratory (Table 2). Mortality in larval collections from control plots 

averaged 7%. (Webb et al. 1990). Larval mortality from different strains, 

doses, and formulations of LdMNPV were evaluated in 1990 following 

hydraulic applications to small forested plots in western Maryland. Larval mortality from Gypchek (75 ± 8%) applied at 2.5 x 1012 OBs per ha 

was not significantly different from larval mortality caused by a similar 

dose of an Abington, MA strain of the virus (80 ± 2%), or treatments 

with a Gypchek formulation containing the sunscreen Orzan LS (73 ± 

6%) (Webb et al. 1993). 

In 1992, a high dose and a low dose formulation of Gypchek, each with 

and without the addition of the activity enhancer Blankophor BBH 

(Shapiro and Robertson, 1992), were evaluated in eastern Maryland, 

again using ground-based hydraulic equipment. Applications of both 

low and high dose formulations containing Blankophor resulted in 

significantly more larval mortality than applications of those formulations without enhancer (Webb et al. 1994). However, more environmental testing of the enhancer will be required before EPA will sanction its use as an inert ingredient in 

biopesticide formulations. The addition of the enhancer to a Gypchek formulation would allow a 10-fold drop in OB dose/

acre, significantly reduce productions costs, and would make more product available for general use. Finally, in 1996 and 

1997, various doses and formulations of Gypchek were applied by ground hydraulic equipment to individual trees in the 

Glassboro Wildlife Management Area, New Jersey (Thorpe et al. 1998). In 1996, the application of a tank mix containing 1 

x 1012 OBs/gal and a sunscreen (Orzan LS) resulted in larval mortality (94.3 ± 3.6%) not significantly different from either 

the same dose without Orzan (81.9 ± 6.0%) or a 10-fold lower dose to which Blankophor BBH had been added (90.5 ± 

4.9%). In 1997 no significant differences were seen in larval mortality resulting from applications of tank mixes containing per gal: 1 x 1012 OBs (98.3 ± 1.7%), 5 x 1011 OBs (88.7± 3.4%) and 1 x 1011 (90.2 ± 3.9%). Also, in both years, live larval 

density was significantly lower on treated trees than on control trees following Gypchek applications. In 1996, defoliation 

Figure 7. Hydraulic treatment of Gypchek to a larval 

infested tree on a home-owner’s property in Maryland. (Roger Zerillo)

Table 2. Average virus mortality in gypsy moth larvae collected from Maryland 

home-owner plots sprayed with Gypchek. Larvae were collected after Gypchek treatments and reared in the laboratory until they either died or pupated.
Ground-based Gypchek Treatments for Gypsy Moth Control

5

of treated trees averaged 8%, significantly lower than 47% defoliation of 

control trees. Defoliation was much lower in 1997, 3% on treated trees 

and 8% on control trees, and not significantly different.

All of the aforementioned field studies clearly showed that extensive 

foliar coverage of the Gypchek formulations was provided by ground 

hydraulic applications (Figure 8). Also, droplet deposition on the 

undersides of leaves provided more shielding of the virus from deactivation by sunlight and a higher probability of larvae ingesting a lethal 

dose than had been observed for aerial applications of the product. The 

current recommended application protocol for Gypchek includes the 

hydraulic application to early instar larvae as soon as hatch is complete 

(Reardon et al. 2016). One application of a water-based tank mix (Table 

3) at 1 x 1012 OBs and 100 gal/acre is recommended for woodlots, roadsides and small acreages, and one application of 15-25 gallons of the 

same tank mix is recommended for individual trees in yards.

Table 3. Gypchek water-tank-mix for ground-hydraulic treatments of gypsy moth larvae.

Ingredient Amount per 3.79 liters (1 gal.)

Tactic1 77.6 ml (2.5 fl.oz.) (2% v/v)

Nonchlorinated water 3.71 liters (125 fl. oz) (98% v/v)

Gypchek 10 billion OBs 1 Adhesive, Synthetic latex, Loveland Industries, Greely, CO

Discussion 

Based on the results of the field tests reviewed here, it is reasonable to assume that topical treatments of egg masses with 

LdMNPV using hand-held pump-up sprayers will result in the death of a significant, if variable, portion of larvae emerging 

from the treated egg masses. If infected first-instar larvae disperse within and beyond the area treated and die on foliage it 

is likely that they will become the source of infection for healthy larvae within and beyond the immediate treatment area. 

However, it is difficult to predict the level of virus-induced mortality that will occur within the area of treatment and in 

the surrounding area. Mortality will be dependent upon the density, rate of development and dispersal of live larvae in the 

vicinity of the treatment area, and favorable weather conditions following viral applications. The application of LdMNPV 

to egg masses, either by manual backpack mist-blower or ground-based hydraulic equipment may be less effective in killing 

larvae and protecting foliage because penetration of the egg masses with virus is lower than when using small, hand-held 

delivery devices. In any case, both the direct, topical treatments of individual egg masses and indirect broadcast treatments will have a measureable negative impact on the larval population, mitigate defoliation and, through environmental 

persistence (Podgwaite et al. 1979), provide a reservoir of virus available for potential impact in the following year. The 

aforementioned studies have also shown that ground-based hydraulic applications of Gypchek that target gypsy moth larvae on individual trees or in small forested plots can be effective in saving foliage and reducing larval numbers and perhaps 

providing positive impact in succeeding years. However, there have not been a sufficient number of small home-owner 

properties treated with Gypchek to predict the impact on future year infestations. Clearly, based upon what is known about 

LdMNPV persistence in the environment and viral epizootiology, there is good reason to believe that Gypchek treatments 

of individual properties, particularly those in close association with one another, would provide a source of virus from 

Figure 8. Hydraulic application of Gypchek to gypsy 

moth larval infestation on a New Jersey roadside 

resulting in extensive coverage throughout the 

overstory and understory and a saturation of the 

undersides of leaves. (Roger Zerillo)
Ground-based Gypchek Treatments for Gypsy Moth Control

6

which larvae could become infected. Of course, more studies are necessary to show the extent to which this may occur, but 

absent those studies there is no downside and little expense incurred when treating properties in anticipation of a certain 

degree of success. 

Why is there a reluctance to institute this technology as part of an overall gypsy moth management strategy? It appears to 

be a logical tool for the gypsy moth management toolbox, particularly in rural and urban environments. The Gypchek label 

states: “Only for use as a biological insecticide to manage gypsy moth infestations in wide-area public pest control programs sponsored by government entities”. The generic statement “.....in wide-area public pest control programs sponsored 

by government entities” implies that Gypchek needs to be applied under government supervision due to safety concerns. 

Gypchek has been documented as having no effects on non-target life forms; it is specific to gypsy moth larvae (Durkin, 

2004). Additionally, ground-based applications do not qualify for cost share as part of the Gypsy Moth Cooperative Suppression and Eradication Program. Both these constraints make it difficult to include ground-based applications as part of 

state and federal requests through the Gypsy Moth Cooperative Suppression and Eradication Program. Gypchek, the only 

gypsy moth-specific insecticide, was developed for use in those areas where the use of broad spectrum products would not 

be appropriate, or perhaps severely restricted. It is best suited for use both in large and in small environmentally-sensitive 

areas that are managed to protect beneficial species and their habitat. 

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