Epizootiological Investigations of the Microsporidium Ovavesicula popilliae and Bacterium Bacillus popilliae in Field Populations of the Japanese Beetle (Coleoptera: Scarabaeidae)

Japanese beetle, Popillia japonica Newman, population densities and prevalence of the pathogens Ovavesicula popilliae Andreadis & Hanula and Bacillus popilliae Dutky are reported from three locations in Connecticut over a 3-yr period. Populations decreased to very low levels (<1 larva/O. l m2)at all three locations, while the prevalence of O. popilliae increased or remained high (>50%). Conversely, prevalence of B. popilliae was <30% throughout most of the study. Ovavesicula popilliae reduced fecundity 50% in heavily infected females in the laboratory. In addition, maximum prevalence of O. popilliae in adults, collected in attractant-baited traps, peaked several weeks after peak adult emergence in the field, suggesting that O. popilliae slows development. However, no differences were detected in the weight or development of field-infected third instars reared in the laboratory. It is suggested that the effect of O. popilliae on its host is modified by environmental stress.