By Erin Hodgson, Department of Entomology
Adult Japanese beetles first emerged in some areas of Iowa around the end of May. This is very early compared to a normal year. At the same time, many other beetles in this large insect family (Scarabaeidae) are becoming active and causing confusion with identification. In general, scarabs are stout beetles that are boxy in shape, have clubbed antennae and thick legs adapted for digging. Adults can be active during the night or day depending on the species; regardless, they are clumsy fliers. Some species are scavengers that feed on dung, carrion or decomposing organic materials; others can be significant plant pests. In most years, adult scarabs emerge mid-June and can be active until August.
Adults are just over ½ inch in length. These scarabs have one generation per year. Probably the most diagnostic features are the white tufts of hairs along the sides of the abdomen and metallic green head and bronze forewings (Photo 1). The forewings do not fully cover the tip of the abdomen. Adults have a very wide host range (>300 plants), including roses, fruit and shade trees, grapes, corn and soybean. Japanese beetles are skeletonizers and feed between leaf veins.
Photo 1. True Japanese beetle. Photo by Dorothy E. Pugh.
False Japanese beetle
Also known as a sandhill chafer, false Japanese beetles closely resemble true Japanese beetles. They are about the same boxy shape and size (½ inch in length). The body is dark brown and shiny (Photo 2), but is not metallic green and bronze. They can have white hair along the side of the abdomen, but the hair is evenly spread out instead of in tufts. These scarabs have one generation per year. False Japanese beetles feed on the flowers, foliage and fruit of many plants, but they are not typically considered field crop pests.
Photo 2. False Japanese beetles. Photo by Marlin E. Rice.
There are several masked chafers in Iowa. These scarabs have one generation per year. Adults are about ½ inch in length and oval in shape. Masked chafers can be dark yellow or tan in color with dark markings on the head (Photo 3). The body, legs and wings can be hairy. Adult masked chafers are not known to significantly feed on plants.
Photo 3. Northern masked chafer. Photo by Mike Reding and Betsy Anderson, USDA-ARS (www.ipmimages.org).
There are several scarabs with the common names of May or June beetles in Iowa. Most have a two to four year life cycle, but some have one generation per year. Adults are 1 inch in length and oval in shape. Body color can range from chestnut brown to red (Photo 4). Adult May/June beetles feed on a wide variety of tree foliage and are not considered field crop pests.
Photo 4. June beetle. Photo by Steven Katovich, USDA Forest Service (www.ipmimages.org).
Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at email@example.com or phone 515-294-2847.
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