Adult Japanese beetles emerge from the soil and live from 30 to 45 days feeding on plants over a four to six week period. Adults feed on many ornamental plants including trees, shrubs, vines, herbaceous annual and perennials, and of course—roses.
Japanese beetle adults are most active during warm days, feeding on plants that are exposed to sunlight throughout the day. This is likely why roses, which require at least six hours of direct sunlight, are such a susceptible host plant. In addition, they tend to initiate feeding at the top of plants, migrating downward after depleting food sources. Japanese beetle adults congregate in large numbers on rose flowers. Adult beetles primarily feed on flowers, but they will also feed on leaves. Japanese beetle adults chew holes in flower buds, thus preventing flowers from opening or causing petals to fall prematurely. Adults will also consume entire rose petals, and feed on the pollen of fully-opened flowers.
Damage to leaves and flowers is easily identified because they skeletonize leaves. Systemic insecticides are recommended as the beetles are may not be feeding at the time of spraying.