Emergence and Reproductive Patterns in the Japanese Beetle, Popillia japonica (Coleoptera: Scarabaeidae)

Sex-biased emergence patterns are common in insects, resulting in either protandry (males emerging before females) or more rarely protogyny (females emerging before males). Previous studies have suggested that the Japanese beetle, Popillia japonica Newman, was protandrous; interestingly, however, they exhibit some characteristics of a protogynous species. For example, Japanese beetles exhibit a last male sperm advantage and females mate and oviposit multiple times. This study investigated the emergence and egg laying patterns of Japanese beetles in east-central Illinois. For both sexes, the size of emerging individuals tended to decline as the season progressed. Overall, female emergence was skewed significantly earlier than that of males. Females did not initiate oviposition until several days after emergence, and the number of eggs laid remained relatively constant over time. Thus, in this population, emergence patterns and reproductive biology suggest that Japanese beetles are not protandrous and may be protogynous.