By Erin Hodgson, Department of Entomology
A few reports of metallic adult beetles have been coming my way this week. I thought it might be too early to see adult Japanese beetles in Iowa. But literally as I am writing this article, a Japanese beetle flies into my office through an open window - guess that answers my question! Some of you may have questions regarding identification of scarab beetles, or beetles in the insect family Scarabaeidae.
In general, adult scarab beetles are stout insects with a hardened body and clubbed antennae. Adults eat a variety of foods, including fungi, dung, carrion, sap, pollen and foliage. Rarely do the adults cause economic damage to field crops, but they can occasionally cause aesthetic damage to ornamental plants and fruit trees. The larvae are called grubs that feed underground or under debris. Larvae are pale yellow, gray or creamy in color, and are always c-shaped. Larvae can cause significant plant damage, particularly to grasses, as they feed on the root system.
Grubs are creamy white with a brown head capsule.1
There are several scarab beetles in Iowa, and probably the most important species is the Japanese beetle. The larvae are difficult to distinguish, but careful examination of the raster (aka, the butt) hairs will provide diagnostic details. The adults are more easily identified based on size and color (see Table 1).
Japanese beetle life cycle.
There is one generation per year, with adults emerging from the soil in June. Mated females lay eggs in the soil until late August. Adults have an exceptionally wide host range (more than 300 plants) and skeletonize leaves. Hatched larvae feed on the roots until temperatures begin to cool in the fall; larvae move deep into the soil to overwinter. Nearly fully grown larvae resume feeding in the spring, pupate within the soil and emerge as adults.
Japanese beetle causes leaves to be bronzed and lacy. Adults often mass on plants.1
The annual cycle of Japanese beetle is like other scarab beetles in Iowa. 2
Table 1. Japanese beetle and other commonly mistaken scarab beetles in Iowa.
1. David Cappaert, Michigan State University (www.ipmimages.org)
2. M. F. Potter, D. A. Potter, and L. H. Townsend, University of Kentucky (http://www.ca.uky.edu/entomology/entfacts/ef451.asp)
3. Marlin E. Rice (/CropNews)
4. Jerry A. Payne, USDA-ARS (www.ipmimages.org)
5. Steven Katovich, USDA Forest Service (www.ipmimages.org)
6. K. V. Makarov (http://www.zin.ru/animalia/coleoptera/eng/aphgrakm.htm)
7. Peter J. Bryant (http://bugguide.net/node/view/272167/bgimage)
Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at firstname.lastname@example.org or phone (515) 294-2847.