UK College of Agriculture, Food & Environment Corn & Soybean News (August 2022)

Dr. Raul Villanueva, Extension Entomologist

Japanese beetles, Popillia japonica (Coleoptera: Scarabaeidae) are native to Asia. This species was first detected in the early 1900s in New Jersey, but now occurs throughout many areas of the United States. This is a well-established pest in Kentucky.

Japanese beetles have only one generation per year. Its larval stage lives underground feeding on roots, with adults emerging in early-July through mid-September. The larval form of this carabid is called white grub.

Adult beetles are considered destructive pests of many ornamentals, turf, and landscape plants. In soy-bean fields, it has been observed feeding on leaf tissue between leaf veins; in many cases this feeding leaves a lace-like, skeletonized appearance. Figures 1A and 1B show initial feeding and advanced skele-tonized leaf, respectively. Leaf damage in soybeans can appear severe as leaves can be completely skel-etonized, and many beetles may be found aggregating on plants in a patchy distribution of the field. However, this injury seldom requires control measures.

At this time, I am reporting a not as well-known feeding habit of Japanese beetles in soybeans. I had heard that this insect was causing some damage to soybean blooms in the North Central region of the U.S. While conducting tallies for insects in soybeans, I observed that a couple of beetles were aggregat-ed under the foliage, and they were feeding on the blooms (Figure 2). Injury to soybean blooms may reduce pod development; however, studies to evaluate the impact of this feeding behavior have not yet been conducted. Feeding on flowers or fruit by Japanese beetles is typical for fruits or ornamental plants.