Influence of Temperature and Moisture on Infection of Forest Tent Caterpillars (Lepidoptera: Lasiocampidae) Exposed to Resting Spores of the Entomopathogenic FungusFuria gastropachae(Zygomycetes: Entomophthorales)

Abstract

Resting spores are critical to the ability of many entomophthoralean fungi to initiate epizootics after periods of host scarcity, but the influence of environmental conditions on their activity is poorly understood. In this study, the effects of temperature and soil moisture on the activity of resting spores of Furia gastropachae (Raciborski) Filotas, Hajek, and Humber, an entomophthoralean pathogen of the forest tent caterpillar, Malacosoma disstria Hubner, were investigated in the laboratory. M. disstria larvae were exposed to soil containing F. gastropachae resting spores under nine moisture-by-temperature treatments designed to approximate the range of ambient abiotic conditions present during the early spring period when host and pathogen are active. Both infection and spore production were maximized at high moisture levels approaching saturation but inhibited in highly saturated soils. The percentage of M. disstria larvae dying from F. gastropachae infections was maximized at cooler temperatures, as was the production of conidia from cadavers. This may be related to host phenology; F. gastropachae maximizes infection and dispersal at the cooler temperatures occurring when its host is active. In this study, a Percoll-based technique for the quantification of entomophthoralean resting spores in soil was applied to determine that resting spore densities exceeded 500/g dry soil, 4 yr after an F. gastropachae epizootic had been observed.