Japanese beetle, Popillia japonica Newman, is an important invasive pest that causes significant damage to golf courses, blueberries, raspberries, hops and many other crops and ornamentals in the eastern United States. This study was conducted to determine the survival of Ovavesicula popilliae-infected larvae compared with uninfected larvae from October to May. Larvae were collected from two sites, one where O. popilliae was active and one where it had not yet been detected. Larvae were placed into plastic sleeve-pots containing 15 cm-diameter cores of turfgrass with roots and soil intact. Larvae collected from both locations were put into sleeve-pots at both locations to account for soil and site factors. Results of this experiment in both years confirm that Japanese beetle larvae infected with O. popilliae do not survive well from October to May. We estimate that at an epizootic location where the pathogen has been active for several years, at least 76.5% of the Japanese beetle larvae infected in October do not survive until May. When the observed amount of population reduction (27-29%) due to natural pathogen infection of larvae in our field plots is combined with a 50% reduction in eggs produced by infected females as previously reported, annual population declines due to O. popilliae would average 40% (assuming a typical adult female infection rate of 25%). This rate of population reduction is consistent with previous reports of Japanese beetle population decline over a period of several years at O. popilliae epizootic sites.