Adults Japanese Beetle Season
Adult beetles typically emerge from the ground sometime between May and June depending on weather conditions of the current year combined with when the season was the year prior. The adult Japanese Beetle typically lives about 30 to 50 days. During this time, the female may lay 40-60 eggs.
Grub Japanese Beetle Season
The season for Japanese Beetle grubs starts about 1-2 weeks after the adult female begins laying the eggs in the soil. The larva develops quickly and are nearly full size by late August. The larva spends about 10 months in the soil as larva before going into a pupal stage and then emerging as adults.