Submitted to: Virginia Gypsy Moth Advisors Annual Review
Publication Type: Government Publication
Publication Acceptance Date: February 19, 1997
Publication Date: N/A
Interpretive Summary: A nuclear polyhedrosis virus has been considered the major pathogen of the gypsy moth in North America; however, a fungal pathogen of the gypsy moth, Entomophago maimaiga, has recently appeared in gypsy moth populations in Eastern North America, often causing massive kill of late-season caterpillars. In 1995 and 1996 we conducted studies in woodlots in southwestern Virginia to quantify the impact the two diseases were having on gypsy moth populations as a function of population density. The present paper is an abbreviated account of our findings intended for an audience of professional gypsy moth managers at the Federal, state, and local levels who need to assess the impact that the new pathogen might have on their programs. In 1995, the highly susceptible, never-before-defoliated woodlots used in this study extended from the defoliating front into the leading edge where the woodlots were still several years away from serious defoliation. Due to the (measured) action of the fungus, and to a much lesser extent the virus, populations in all woodlots fell dramatically without causing the high levels of defoliation that had been expected in the high density plots on the defoliating front, nor did the low density plots just within the leading edge undergo normal gypsy moth population buildup. The finding that E. maimaiga can cause the crash of leading edge gypsy moth populations indicates that the spread of this serious forest defoliator may be slowed because of reduced population pressure at and beyond the defoliating front. This development should facilitate the success of the USDA's Slow-The-Spread project.
Studies were conducted in "leading edge" woodlots in SW Virginia to quantify the impact that two diseases (gypsy moth NPV and the fungus Entomophaga maimaiga) were having on gypsy moth populations as a function of population density. Ten woodlots were chosen to reflect a range of population densities. Season-long total larval mortality (all sources) was calculated based on the number of larvae that died during the week after each collection. In 1995, levels of the fungus were high in all plots regardless of gypsy moth density, while virus levels were clearly higher in the high density plots than the low density plots. In 1996, the virus was not a factor in the continued decline of the gypsy moth populations in all plots, while fungal impacts remained strong.