Role of feeding-induced plant volatiles in aggregative behavior of the Japanese beetle (Coleoptera: Scarabaeidae)

The hypothesis that feeding-induced plant volatiles are responsible for aggregation of Japanese beetles, Popillia japonica Newman, on leaves was tested using clonal grape plants, Vitis Labrúsca L. The attractiveness of undamaged vines, undamaged vines with nonfeeding beetles, vines with fresh feeding damage, and vines with overnight feeding damage was compared in replicated field trials by placing the treatments in the field in the morning and counting the number of beetles that landed on the plants throughout the day. Many more beetles were recruited to vines with overnight feeding damage than to any of the other treatments, indicating attraction to feeding-induced volatiles. Furthermore, the low number of beetles attracted to vines with nonfeeding beetles or freshly damaged vines provided evidence against the existence of a putative aggregation pheromone. Subsequently, we examined the emission of volatiles from grape vines in situ. During the period of peak emission (1200-1500 hours), emission from vines with overnight feeding damage was almost 65 times higher than from undamaged vines. Aliphatic compounds and terpenoids were the major classes of compounds emitted by the beetle-damaged vines. The implications of feeding-induced volatiles in host-finding and mate location by this polyphagous insect are discussed.