Over the past 2 days, several reports have come in indicating that Japanese beetle adults are beginning to emerge. Adult Japanese beetles have been found from the southern tip of the state (Ron Hines reported 16 adults in his trap) all the way to central Illinois, where several observations have been made. On June 23, Brad Lindquist spotted them in Mechanicsburg; Dennis Bowman, Extension educator in crop systems, found not only an adult but several pupae that were very close to emerging in McLean County. Once again, in the research plots, the IPM graduate students and Ron Estes, coordinator of the insecticide efficacy trials, reported Japanese beetle adults in Piatt County; adult beetles were also spotted in cornfields in Champaign County near Rantoul by Brad Burnett, Pioneer, on June 24.
Japanese beetle adults pupate and emerge as adults in mid- to late June. During the summer months, females will mate several times during their 30- to 45-day life span. Females lay eggs in mid- to late summer. Larvae hatch and feed on root systems of various host plants in the fall. They overwinter as third instars deep in the soil. As temperatures warm in the spring, the grubs move back toward the soil surface, where they feed on organic matter and corn roots until late spring when they enter the pupal stage. Japanese beetles have only one generation per year.
Last year, Japanese beetles drew a lot of attention due to the massive numbers that were present in July and August. Many reports of beetles feeding in corn-fields made their way to the Bulletin last summer. Joe Spencer, Center for Economic Entomology, Illinois Natural History Survey, and Scott Isard, Department of Geography, sampled soybean fields in all counties in the state of Illinois in 2002. The results of their sweep-net samples are presented in Figure 1 (see page 134), with the map illustrating which counties had beetle infestations. Beetles were present in 59 Illinois counties.
The presence of Japanese beetle adults should serve as a heads-up for growers across the state. As the beetles continue to emerge, they will begin seeking host plants to feed on, including corn and soybeans. Economic damage may be caused by silk clipping in corn and defoliation in soybeans. Continue to watch the Bulletin for future updates on this insect.--Kelly Cook