Japanese beetles are important pests of many agricultural and horticultural plants, yet few studies have attempted to follow the mating behavior of individuals in the field. In this study, we recorded mating behavior and patch residence of Japanese beetles on food plants under field conditions. Pairs of beetles were marked and their fates were followed for 2 days. Both male and female Japanese beetles frequently mated with more than one individual, with males being more likely to pair multiply than females but females more quickly re-pairing than males. Patch departure differed between males and females, with females tending to leave the food patch in midday and males tending to leave in the evening. Male mate-guarding of females was highly variable, with some males remaining with females less than 30 minutes and others guarding females for over 24 hours. The duration of mate guarding was unrelated to whether the female departed immediately after the pair broke up. The results of this study suggest that individual turnover in food patches is high and that there is substantial opportunity for sperm competition.