Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

5/31/04

Contacts:
Laura Jesse, Entomology, (515) 294-7400, lrahnsen@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu
Garden Column for the week of June 4, 2004

June Bugs Prepare to Emerge

By Laura Jesse
Graduate Assistant
Entomology

Nothing says spring in Iowa quite like a big brown beetle smacking into your forehead as you spend a pleasant evening lounging on the front porch. Who are these beetles that seem so transfixed by the lights around our homes? If you are like most of us, you call them June bugs and don't give them much more thought. However, the world of brown beetles is actually quite interesting.

June bugs belong to a large group of insects called scarab beetles. There are actually at least two species of "June bug" normally found around lights in Iowa. The larger beetles are called May or June beetles and are members of the insect genus Phyllophaga. They are called May or June beetles because the adults emerge and subsequently arrive at our lights in May and June. They are about .5 to 1 inch long and dark brown. The second species is the northern masked chafer, Cyclocephala borealis. This beetle is smaller, about .5 inch long, and a lighter tan color. The northern masked chafer will emerge in late June and you will be able to find them circling a light near you.

The adult northern masked chafer and June beetles feed on trees and other plants, but generally do not cause enough damage to be considered pests. The damaging stages of these beetles are their larval stages. Female beetles burrow into the ground several inches to lay their eggs in the soil. The larvae hatch about two to four weeks later and begin feeding on plant roots. The larvae of both beetles are C-shaped white grubs. Larval May or June beetles are called true white grubs, and take three years to develop from eggs to adults, spending most of their lives as grubs. True white grubs can be a pest of row crops.

The larvae of the northern masked chafer are called the annual white grub and will develop from egg to adults in a single year. Annual white grubs are not generally a pest of row crops. They tend to be a more serious pest of turfgrass. Damage from annual white grubs to your lawn will first appear as wilting and tan discoloration. Later in the summer symptoms can vary from small-discolored patches to large, irregular dead areas. However, the damage can be confused with other pests and diseases, so pull back the sod to confirm that grubs are feeding on the grass roots. Often, areas of damage are near a light, which attracted the female beetles at night. Keeping lights turned off at night, especially during those times when the adult beetles are numerous and active, can help reduce damage. In addition, yellow light bulbs are less attractive to insects than white or mercury vapor bulbs.

There is another scarab beetle in Iowa that is also a serious pest, the Japanese beetle. The Japanese beetle is an attractive metallic green and bronze beetle. This beetle has been slowly working its way across the eastern United States since its introduction on the East Coast in the 1910s. Japanese beetles also have C-shaped grub larvae that are a turfgrass pest. Adult Japanese beetles are also a major pest because they feed on many agricultural and ornamental plants, including roses, grapes and linden trees. Japanese beetles arrived in Iowa several years ago and seem to cause the most problems in the eastern half of the state. Unlike our native scarab beetles, Japanese beetles are not strongly attracted to lights at night.

So, why are insects attracted to lights at night? To be honest, we have some ideas, but we are just not sure why. We are fairly certain that it has to do with navigation. It appears that some insects use light from the sun or moon to navigate. Entomologists think they do this by keeping the same angle between themselves and a specific light source - similar to the way sailors use the stars. This works well when the actual light source is very distant and you are never going to get anywhere near it. However, artificial lights are here on earth and an insect using a streetlight to navigate by can simply fly right past it! The insect may then begin to circle the light in an effort to maintain the appropriate angle between itself and the light.

We can observe the behavior of insects and make some educated guesses as to what they are doing. However, we have no real way of knowing what is actually going on in their brains as they orbit your porch light on a pleasant spring evening.

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ml: isugarden

Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 188K. Caption: June beetle. Photo by Laura C. Jesse.

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