Meteorological factors affecting the success of the gypsy moth fungal pathogen Entomophaga maimaiga (Zygomycetes: Entomophthorales) in Michigan

The fungal pathogen Entomophaga maimaiga (Zygomycetes: Entomophthorales) has been responsible for significant declines in gypsy moth [(Lymantria dispar L.) (Lepidoptera: Lymantriidae)] population density in the northeastern U.S. since 1989. In Michigan, however, the pattern of E. maimaiga epizootics has been less consistent since its introduction in 1991. Although E. maimaiga is established throughout Michigan, high-density gypsy moth populations and severe defoliation have continued to occur. As the gypsy moth fungus is highly sensitive to variations in temperature and moisture, more information is needed concerning E. maimaiga infection rates in relation to climate in the North Central region of the United States. Meteorological factors affecting the success of E. maimaiga were examined using large-scale climate-matching analyses, and laboratory and field bioassays between 1999 and 2002 that compared E. maimaiga infection rates under optimal versus naturally-occurring conditions. Additionally, E. maimaiga and nuclear polyhedrosis virus infections of gypsy moth larvae during primary transmission were evaluated in an oak-dominated Michigan forest with low-density gypsy moth populations. Infection rates during 4-d intervals were related to microclimatic variables occurring over a 6-wk period of gypsy moth larval development.; A relatively small area in the southern Great Lakes region was determined to be highly similar in long-term climatic patterns to the climatic conditions in regions of the U.S. where large-scale E. maimaiga epizootics have been documented. A high degree of climatic variability, however, occurs annually in portions of the North Central region. The number of years between 1971 and 2000, in which weather may have been favorable for the development of E. maimaiga epizootics in the North Central region, were estimated.; Bioassays using laboratory-reared 4th-instar gypsy moths were conducted to evaluate E. maimaiga infection rates in oak-dominated forests in Michigan. In field bioassays, infection rates of E. maimaiga were significantly lower under naturally-occurring conditions in Michigan than under laboratory conditions that were optimal for fungal germination. Increased levels of E. maimaiga infection in field bioassays were associated with June temperature and precipitation levels which were significantly greater than 30-year average conditions. Dynamics of E. maimaiga throughout much of the North Central region appear to be primarily limited by weather, specifically levels of June precipitation. The role of climatic variability in the success of E. maimaiga in the North Central region are discussed. Implications of this research for developing improved methods and recommendations to incorporate E. maimaiga into an integrated pest management system for the effective control of gypsy moth in forest ecosystems in the North Central region are presented.