Feeding of Japanese Beetles on Soybean also Cause Injuries to Blooms

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 soybean 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 skeletonized leaf, respectively. Leaf damage in soybeans can appear severe as leaves can be completely skeletonized, 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 aggregated 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.