No. 10 Article 4/June 1, 2007

Japanese Beetles Have Begun to Emerge in Southern Illinois

Most people in southern Illinois, rural and urban alike, won't wish to remember the headaches caused by Japanese beetles last year. However, because the survival of Japanese beetle grubs over the winter is difficult to predict, everyone should be on alert. Early indications are that Japanese beetles survived the winter quite well, at least in southern counties, which suggests that we should be prepared. And being prepared means, in part, knowing when the beetles emerge.

Emergence of Japanese beetles has been confirmed in southern Illinois. Ron Hines, FS seed agronomist for Growmark's southern region, reported the capture of three Japanese beetle adults in a trap in Massac County in extreme southern Illinois on May 28. The trap actually had been in a yard but now has been moved into the "trap line" for Massac County. Traps for Japanese beetles and western corn rootworm adults will replace the armyworm and black cutworm traps at all six locations--Fayette, Jefferson, Massac, Pope, Pulaski, and St. Clair counties.

Commercial Japanese beetle trap with floral and sex pheromone lures (photo courtesy of Ron Hines, formerly with the University of Illinois).

Japanese beetle adults are approximately 1/2 inch long and are metallic green with bronze-colored elytra (wing covers). Just below the edges of the wing covers on the sides of the abdomen are five tufts of white hair, and there are two tufts of white hairs on the rear of the abdomen. People in areas with sandy soils should not confuse Japanese beetles with false Japanese beetles. These two species are closely related, and their appearances are similar. However, the Japanese beetle is more iridescent than the false Japanese beetle, and the false Japanese beetle lacks the characteristic tufts of white hair. False Japanese beetles typically do not cause significant injury to corn or soybeans.

Japanese beetle adult (photo courtesy of Joe Spencer, Illinois Natural History Survey).

And so it begins. It seems a bit early for emergence of Japanese beetles, but temperatures during May have sped up insect development in many areas. So maybe it's not too early to review a little Japanese beetle biology. The following information was extracted from "Biology and Management of the Japanese Beetle" by D. A. Potter and D. W. Held (Annual Review of Entomology, 2002, 47: 175-205).

Male Japanese beetles begin to emerge a few days earlier than females. The males mate with virgin females almost immediately after the females emerge from the soil. The females probably lay a few eggs for about three days soon after mating, even before they feed. Afterward, however, females fly to host plants to feed and remate. They then alternate between periods of feeding and of oviposition. Individual adult Japanese beetles live for 4 to 6 weeks.

Japanese beetle adults feed on foliage, fruits, and flowers of more than 300 species of wild and cultivated plants. The beetles are attracted to hosts by volatiles emitted by the plants, often when the plants are flowering. In addition, the feeding by a few Japanese beetles on a host plant will attract others, which helps explain the large numbers of beetles that seem to congregate on given host plants. Both sexes of Japanese beetles are strongly attracted to blends of plant volatiles released from beetle-damaged leaves.

Because large aggregations of Japanese beetles are attracted to flowering corn plants, it is critical to watch for silk clipping by adults in pollinating corn. In soybean fields, the primary concern is defoliation. In forthcoming issues of the Bulletin, we will discuss scouting for Japanese beetles and making decisions about their control. In the meantime, you can review our Japanese beetle fact sheet (Adobe PDF, 184 kb).-- Kevin Steffey

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