JULY
1994

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

7-14-94

Japanese Beetles: Pretty But Pesky

Today I discovered a beautiful beetle. It was about .5 inch long and metallic green to greenish bronze with reddish wing covers. Such a fine suit requires the proper accessories, and the beetle provided them with two prominent white spots near the tip of the abdomen as well as several smaller white spots along the sides.

In fact, I discovered more than one of these beetles. I discovered dozens of them, and they were all feeding on my roses. These weren't just any old beetles, these were Japanese beetles, the scourge of many gardeners in the eastern United States.

Beautiful though they may be, Japanese Beetles are serious pests of lawns, fruits and vegetables, and ornamental plants.

The Japanese beetle was imported into New Jersey from Japan in about 1916. It arrived on the roots of nursery stock. From this introduction, the insect spread to all states east of the Mississippi except Florida.

The adult Japanese beetle feeds on the foliage and fruits of more than plant 300 species. Plants attacked include almost all fruit and shade trees, corn and soybeans, and many ornamental crops. Roses are one of their favorite foods, much to the concern of gardeners who are rose fanciers.

Grubs of the beetle feed on decaying vegetation and the roots of grasses and other plants. Because of the grass feeding habit, the grubs can sometimes cause severe damage to lawns. The beetles are most common in July and August. They lay eggs in the soil. The newly hatched grubs begin to feed and will grow until winter. During the winter, the grubs move deep enough in the soil to avoid the winter temperatures. The next spring, the grub moves back to the surface and feeds until it changes into an adult and emerges at the end of June to begin the cycle again.

Most people try to get rid of the adult Japanese beetles, and that is not an easy task because for every one that is killed it seems there are at least two to take its place. The best approach is to protect ornamentals with an insecticide spray, although this will have to be done frequently during July and August. For homeowners who want to protect the lawn from grub damage, it is best to wait until August when all of the eggs have been laid before treatments are applied.

Some people are tempted to try and control Japanese beetles with the traps that are sold for that purpose. These traps use combinations of floral and insect odors to attract the beetles. They attract the beetles alright — by the thousands they end up in the traps. Research has shown that the traps really don't do much for the homeowners problems. The traps attract more beetles than they kill. However since Japanese beetles are such a tough problem for most people, they do take some small pleasure in knowing they have killed some of the maddening swarm.

 

Writer: Tom Turpin
Editor: Andrea McCann