Comparison of Aerially-Applied Gypchek Strains Against Gypsy Moth (Lepidoptera: Lymantriidae) in the Presence of an Entomophaga maimaiga Epizootic

Abstract

The standard strain (LDP-226) of Gypchek®, a nucleopolyhedrovirus product registered by the USDA Forest Service against the gypsy moth, Lymantria dispar (L.), was compared against a strain, LdMNPV-203NL (NL = nonliquefying), that was developed for production in cell culture. Both strains were applied by air to U.S. government property in Prince Georges Co., MD, in early May 2003 at the rate of 1 × 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 suppressed 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.