The 1/2-inch-long copper and green adult Japanese beetles, Popillia japonica (Newman), may appear in large numbers at harvest in late June to feed on the leaves. Leaves on the upper parts of the cane are affected more severely, and different varieties of raspberries vary in their susceptibility to beetle attack. Infestations peak in July but can continue through September. Japanese beetles spend the winter and spring as larvae in the soil, feeding on grass roots.
Beetle feeding can be controlled with broad-spectrum insecticide applications if necessary; however, beetles can fly substantial distances from untreated overwintering sites such as pastures and reinfest plantings. Weekly inspections of plantings therefore are recommended from harvest onward.