Inoculative augmentation of the fungal entomopathogen Entomophaga maimaiga as a homeowner tactic to control gypsy moth (Lepidoptera: Lymantriidae)

Abstract

Resting spores of the gypsy moth fungal pathogen Entomophaga maimaiga were introduced to four treatment plots on the eastern shore of Maryland in 1995 and 1996 to augment the naturally occurring fungal population. Efforts were focused on small woodlots, characteristic of homeowner properties, where the most intensive management of gypsy moth populations is often practiced. To evaluate results, larvae were sampled from the understory vegetation, under burlap bands, and in the tree canopy. Survival of fifth- and sixth-stage gypsy moth larvae was always lower in treatment versus control plots although differences were statistically significant on only four of twelve sampling dates (P < 0.05). Infection by E. maimaiga was always greater in treatment than in control plots, but due to high variability among plots, these differences were not significant. During 1995, severe defoliation occurred in only one control plot, and numbers of fifth instars were positively associated with the defoliation level. During 1996, no defoliation occurred in any plot because the gypsy moth population collapsed throughout the area, This is the first study sampling gypsy moth larvae throughout the tree canopy to compare the relative distribution of larvae infected by E. maimaiga and the Lymantria dispar nuclear polyhedrosis virus (LdNPV). Third through fifth- and sixth-stage gypsy moth larvae infected with E. maimaiga were more abundant in the understory vegetation than in the tree canopy. Larvae infected by LdNPV demonstrated a trend later in the season toward increased occurrence in the tree canopy than in the understory vegetation, although results were not significant.