Demonstrating an increase in preference for young growth by Japanese Beetles, Popillia japonica Newman, in Wisconsin grape vineyards

The Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), an exotic, introduced scarab, is a widespread and destructive insect pest of turf, landscapes, and nursery crops in the eastern United States. It also damages many fruit, garden and field crops. This study investigated the population of Japanese beetles on grapes with varying amounts of young leaves. Grape plants with greater amounts of young growth showed an increase in the number of adults present on the plant compared to plants with a greater amount of older growth. Japanese beetle adults also significantly preferred younger leaves over older leaves in a choice test. Young and old leaves were examined to evaluate potential attributes that may be attributable to adult preference for leaves; a leaf penetrometer was used to measure the toughness of leaves. Younger leaves required significantly fewer grams of pressure to puncture through the leaf tissue than older leaves. Young and old leaf samples were collected and examined to measure and compare the amount of Carbon, Nitrogen, and Hydrogen in the leaf tissue. Younger leaves showed a significantly larger amount of Carbon and Nitrogen, older leaves exhibited significantly larger amount of Hydrogen. The results of this study suggest that the removal of younger growth, may provide a potential management tool for reducing Japanese beetles from grape plants.