Problem
In a recent regional meeting of entomologists working in field crops, I learned of the increase abundance and attacks of the Asiatic garden beetle, Maladera castanea (Coleoptera: Scarabaeidae) in corn fields in southwest Michigan, northwest Ohio, and Indiana in 2018. Dr. Christina DiFonzo reported damages in 2017 and 2018. She reported that fields were affected in many locations after delays due to cold and extremely wet conditions (Figure 1). The Asiatic garden beetle is a species of Asian origin and was reported first in the northeast U.S. in the 1920s. Adult beetles feed on foliage and blossoms of many plant species, including vegetables and ornamentals. Grubs feed on roots of grasses and can persist in weeds even if corn is present. However, if herbicides are applied, grubs move on to corn and damage can occur overnight. Adult feeding also occurs at night. DiFonzo described the Asiatic garden beetle feeding on some weed species that includes marestail, purple deadnettle, chickweed, pokeweed, and Virginia creeper.
Figure 1. Aerial view of a field in Monroe County, Indiana showing a thin stand and yellowing (the thin, yellow areas are a replant). An average of 2 Asiatic garden grubs per cup cutter were found in this site, but 6 to 7 per cutter were found in hot spots. (Photo: Ricardo Costa, Michigan State University Extension).
The Asiatic Garden Beetle Life Cycle
The Asiatic garden beetle, Japanese beetle, and Junebug are in the subfamily Melolothinae, thus, some characteristics among these species are common. However, Asiatic garden beetle eggs are laid in the soil in clusters of up to 20, held together by a gelatinous material. The larva, is a typical C-shaped six-legged grub, whitish to creamy in color with a brown head capsule, and six legs. A distinctive characteristic of the larva is the presence of a bulb in the face (Figure 2), not present in other common scarabaeids (Japanese beetles, May June bugs or chafers). Late stage grubs are 3/4 inch long. The adults are 3/8 inch long, a brown color that can be iridescent, and the wing covers (elytra) do not entirely cover the abdomen. They emerge in late June or July and can be found until the end of fall. Adult beetles are nocturnal, so they are seldom seen on host plants where damage occurs. At dusk, beetles leave the ground, where they have been hiding during the day.
Figure 2. Distinctive bulbous stipe on Asiatic garden beetle grub. (Photo: J. Obermeyer from Michigan State University Extension publication CDD-034)
Management
Farmers that plant corn in sandy fields should check for this pest species if damage is present. Studies from Vermont, Indiana, and Michigan show that garden Asiatic beetles prefer sandy-loam soils. Insecticides apparently are not effective; Dr. Difonzo saw high percentages of survival at low, medium, and high (250-500-1250) rates of seed treatment and Lorsban. Even with tillage, grub populations were not reduced.
More Information
- Asiatic Garden Beetle (University of New Hampshire Cooperative Extension)
- Attack of the Asiatic garden beetles in field crops (Michigan State University)
- Asiatic Garden Beetle Potential Problem in Northern Ohio Corn Fields, Sandy Soils (The Ohio State University)
- Asiatic Garden Beetle Damage Reported! (Purdue University Extension)
- Asiatic Garden Beetles May Cause Corn Field Yield Losses in Southwest Michigan (Michigan State University)
By Raul T. Villanueva, Extension Entomologist
Kentucky Pest News 