Abstract
Infectious activity of hibernated resting spores of Entomophaga maimaiga in the field was bioassayed on gypsy moth larvae at the site where an epizootic had occurred the previous year. Mortality of the larvae with this fungus was 7.5 to 14.0% when they were exposed to the cadavers on a tree trunk for 1 night. Suspensions of the cadavers, litter, and soil, which were collected from the field and were thought to contain resting spores, had infectious activity to the larvae, i.e., 4.0 to 12.0% of them were infected with the fungus. When the larvae contacted those materials during rearing, 8.0 to 44.0% of them were also infected. The larvae were not infected in the experiments with resting spores 2 years old. No larvae in the control plot were infected in any experiment. From those results, it was ascertained that the infection of young larvae with overwintered resting spores initiated the epizootic in the population of gypsy moth with E. maimaiga.
