A Tale of Two Beetles

Names of insects are a common source of confusion, in part because gardeners are prone to nickname plants and animals they see, and many common names sound similar. Such is the case with two invasive insects found in Iowa, both relative newcomers to the landscape. 

The Japanese beetle (Popillia japonica) is a plant-feeding Junebug found in a limited number of places within the state. Adult beetles are found feeding on plant flowers, foliage and fruit during mid-summer. 

The other newcomer, multicolored Asian lady beetle (Harmonia axyridis), has a lengthy official name that is reminiscent of Japanese beetle, and as such, is frequently misnamed. Multicolored Asian lady beetle (or ladybug ˆ a synonym) is a beneficial predator that eats aphids and other small insects in trees and fields during the summer. It is found everywhere in the state, and has the unfortunate habit of migrating to houses in the fall when the day-lengths shorten. They accumulate on the sunny sides of the building and wandering indoors, becoming an annoying, though harmless, household nuisance.

The Japanese Beetle

In the eastern United States the Japanese beetle (Popillia japonica) is the most destructive insect pest in the landscape and garden. It was 91 years ago in 1916 that the Japanese beetle was first found in this country, near Riverton, New Jersey, after arriving in nursery stock from Japan. Japanese beetle infestations slowly expanded southward and westward to cover most of the eastern one-half of the United States

The Japanese beetle did not appear in Iowa until 1994 and is still only been reported from 20 counties in the state (see list). The small, isolated infestations scattered across Iowa are an indication that the Japanese beetle was spread with infested plants and not by natural dispersal.

The Japanese beetle's distinction as the worst landscape pest in America comes from its ability to attack plants and be a serious pest in both the adult and larval stages. As an adult beetle in mid-summer, the beetles are known to devour the foliage, flowers, and fruit from more than 400 species of plants. The rest of the year the larvae are white grubs that live in the soil and eat the roots from trees, shrubs and turfgrass. Damaged turf wilts, turns tan and dies during August or September after the roots are eaten.

The Japanese beetle is a member of the large and varied family of scarab beetles, the well-known and familiar "junebugs" seen circling the porch light on warm evenings from spring through early summer. Japanese beetles are blocky and a little less than one-half inch-long and about one-quarter inch wide with a hard shell. The front of the body is shiny, metallic green while the wing covers are copper or bronze. Small white tufts of hair along the sides and back of the abdomen distinguish the Japanese beetle from similar insects.

The adult beetles begin to emerge from the ground during the last week of June and new adults continue to appear throughout July. Each beetle lives from only 30 to 45 days but adults may be present for most of a 6-week period throughout mid summer.

Though they may eat almost any plant ranging from roses to poison ivy, they have a few favorites. Look for them first on roses and other flowers, raspberries, grapes and crabapple and linden trees. 

Control of Japanese beetles is difficult. Persistence, diligence and repeated efforts are necessary because beetles emerge every day for a period of several weeks. Handpicking or screening of high-value plants may be of benefit in isolated situations with limited numbers of beetles. Remove beetles early and often to preserve the beauty of the plant and to reduce the attraction of more beetles. Remove beetles early in the morning while temperatures are cool and the beetles are sluggish. Collect or shake beetles into a bucket of soapy water and discard.

Spot spraying infested foliage of high value plants with a labeled garden insecticide may reduce damage for several days, but multiple applications are required to maintain control. Check the insecticide label to make certain the plant you want to spray is listed. Read and follow label directions.

Although Japanese beetle traps are widely available, research conducted in Kentucky suggests that they are not effective in controlling moderate to heavy infestations; and they may attract more beetles into a yard than would occur otherwise. Japanese beetle grubs can be controlled with an appropriately timed application of a registered turfgrass insecticide. Spraying the adult stage is not an effective strategy for prevention of white grubs.

List of counties where JB has been documented in Iowa. Beetles are not in all areas within reported counties. Most counties have a few to several infested areas. Worst areas of the state are Dubuque, Davenport, Cedar Rapids, and Iowa City. Some counties have reported one or two beetles but none were found in subsequent years.

Black Hawk Lee Boone Linn Clayton Madison Clinton Marshall Dallas Muscatine Dubuque Page Floyd Polk Iowa Scott Jackson Story Johnson Woodbury

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Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on February 21, 2007. The information contained within may not be the most current and accurate depending on when it is accessed.