The When and The Where of Japanese Beetle Injury
Illinois Natural History Survey
Graduate Research Assistant
Department of Crop Sciences
Technology Transfer Specialist, Insect Management
Indianapolis, IN 46268-1054
The Japanese beetle, Popillia japonica, was accidentally introduced into the United States; it was first detected in southern New Jersey during 1916. This pest is now widespread throughout most states east of the Mississippi River and portions of Iowa, Minnesota, and Nebraska. Popillia japonica was first reported in Illinois in the early 1930s; climatic conditions in the eastern United States have promoted the spread of this insect. Japanese beetle infestations have been on the rise recently; the United States Department of Agriculture and Illinois Department of Agriculture are instrumental in initiating tactics to keep infestations from reaching economic thresholds.
Japanese beetle adults have become a familiar, though unwelcome, feature of summertime in Illinois. Highly mobile, the 0.75 inch long, green and copper-colored beetles are famously known to feed on hundreds of different plant species. The adult males are first to emerge from the soil, followed by the females a few days later. Females lay their eggs beginning in mid-to-late June and continue through August; there is one generation per year. During its four to six week adult lifespan, a female Japanese beetle will lay 40-60 eggs. In soybean fields, females lay their eggs within the upper 3 inches of soil; there is also some egg laying in cornfields. Egg development and maturation is favored by moist weather conditions and extremely dry environments have the capability to eliminate most eggs. Unfortunately, Japanese beetle females can response to periods of dry weather and deposit their eggs in other moist areas, such as low lying poorly drained spots. Japanese beetle eggs hatch within two weeks of deposition and the larvae begin to feed on plant roots. The immature, a white grub with a brown head capsule, is full grown at ca. 1 inch long. The Japanese beetle white grub can be identified by looking at the hair pattern on its last abdominal segment called the ‘raster’. A v-shaped hair pattern is diagnostic of a Japanese beetle white grub. Each stage of grub development takes about two to three weeks to complete; larvae overwinter in the soil.
Japanese beetles can have a very dramatic effect on soybeans. Almost all soybean feeding by Japanese beetle occurs during the plant’s reproductive stages. The feeding adults are most active during mid-morning to late afternoon with sporadic feeding in the evenings. Popillia japonica feeding activity peaks under clear conditions, in a temperature range from 84 to 95 degrees Fahrenheit, relative humidity of less than 60%, and when winds are less than 12 mph.
Our 2009 Japanese beetle sampling project is funded by the Illinois Soybean Association and involves on-farm cooperators from across the state. Our goal is to develop a visual threshold for Illinois farmers and operators to use when determining if a Japanese beetle infestation warrants treatment to protect yield. Our wide scale sampling is focusing special attention on the number of Japanese beetles present at the field edge vs. the interior. We are also doing leaf defoliation studies to link plant injury, beetle abundance, and grain yield. A better understanding of when and where Japanese beetle injury occurs will help us develop a useful tool to manage this pest’s impact in soybean fields.
This project is funded by the Illinois Soybean Association.
Defoliated portion of a soybean field.
Japanese beetles feeding on soybean leaf.