Submitted to: Journal of Entomological Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/20/2005
Publication Date: 10/1/2005
Citation: Webb, R.E., White, G.B., Podgwaite, J., D'Amico, V., Slavicek, J., Swearingen, J., Onken, B., Thorpe, K. 2005. Aerially-applied baculovirus and naturally-occurring entomophaga maimaiga provide outstanding control of gypsy moth (lepidoptera: lymantriidae). Journal of Entomological Science. 40(3):446-460. Interpretive Summary: Gypchek, a product with the Lymantria dispar multienveloped nucleopolyhedrosis virus (LdNPV) as the active ingredient, is registered by the USDA Forest Service with the U. S. Environmental Protection Agency as a general use bioinsecticide. Gypchek, as currently produced in vivo, has limitations. It is expensive to produce, contains extraneous material, and lacks potency at doses more affordable than those currently prescribed. A strain of LdNPV, designated LdNPV-203, is stable in cell culture and, in laboratory bioassays, is more potent than Gypchek. However, LdNPV-203 does have one characteristic that may bear upon its further development; larvae killed by this strain do not 'liquefy' after death in the manner that is associated with Gypchek-killed larvae, with potentially negative implications for the 'horizontal' transmission of LdNPV-203 in the year of treatment. This indicated that if LdNPV-203 were to be used for gypsy moth suppression the second wave of mortality that comes from healthy larvae feeding on inoculum from larvae killed by the spray might be blunted. To test the hypothesis that an LdNPV-203 aerial application would affect a second wave of mortality, we monitored a set of plots within treatment blocks that were treated aerially either with Gypchek or with LdNPV-203. The operational goal of the study was to compare Gypchek and Strain 203 from the air. The test was to be considered successful if 203 performed as well as Gypchek. Gypchek and strain 203 gave equivalent control when both were applied under appropriate conditions. The level of early season suppression due to the applied virus, combined with high late-season mortality caused by the gypsy fungal pathogen Entomophaga maimaiga, resulted in the elimination of the gypsy moth from the area. Thus, the applied Gypchek + natural E. maimaiga system, which only kills gypsy moths, can be considered an outstanding example of applied biological control in areas where the fungus is established. This work is of interest to managers of forested tracts, arborists, and homeowners with susceptible shade trees.
Technical Abstract: The standard strain of Gypchek was compared against a strain, LdNPV-203, that was developed for production in cell culture. Both strains were applied by air to United States government land in Prince Georges County, MD in early May, 2003 at the rate of 1 X 1012 occlusion bodies per ha. The two goals of the study were (1) to compare the first and second wave effects of the two strains against gypsy moth populations; and (2) to delineate the combined effects of the applied virus and the expected epizootic of the gypsy moth specialist fungal entomopathogen Entomophaga maimaiga Humber, Shimazu, and Soper. Heavy rainfall in May and June preceded a massive epizootic of E. maimaiga, whose effects did not mask the first wave of viral mortality. When the effect of application sequence was considered, it was concluded that the two strains were equivalent in their first wave impacts. High fungal-induced mid- and late-season gypsy moth larval mortality dampened the second wave of virus at all evaluation sites. There were no obvious differences in the second waves engendered by the two LdNPV strains in the greatly reduced late-instar larval population. The combined efficacy of the applied viral and the natural fungal pathogens in wet and dry years are discussed.