The dreaded Japanese beetle is back

StoryImage( ‘/Images/Story//Auto-img-118592372032194.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘Japanese beetles voraciously attack the leaves of about 250 different species of plants.‘);
StoryImage( ‘/Images/Story//Auto-img-118592378323019.jpg’, ‘Photo courtesy of‘, ‘The Japanese beetle showed up on our shores for the first time in 1916, when it was discovered in a plant nursery in Riverton, N.J., just across the Delaware River from Philadelphia.‘);

The other day, I was walking around my yard when I suddenly had the squeamish feeling something was moving through my hair. Running my fingers through my top knot, I retrieved a Japanese beetle that had somehow selected the top of my head to be a landing strip. Japanese beetles bug me as I recall unpleasant encounters with them in the past, such as destruction of plants in my garden, and some years ago causing me to lose a golf tournament. In the latter instance, I only needed to make a 6-foot putt to win. Though I hit the putt straight for the hole, it veered off and missed at the last moment. It had been deflected by a pair of Japanese beetles blissfully engaged in the mating process a few inches from the hole. If we could deport undesirable alien insects as we sometimes do with undesirable people, the Japanese beetle would be first on my list to be expelled.

Many people believe this destructive beetle was introduced into the United States with the cherry trees the Japanese government gave us to adorn the Tidal Basin in Washington, D. C. Actually, this Asiatic immigrant showed up on our shores for the first time in 1916, when it was discovered in a plant nursery in Riverton, N.J., just across the Delaware River from Philadelphia.

As it had no natural enemies in this country, it quickly gained a foothold in the environment and flourished. It is generally found today east of a line running from southern Michigan to southern Wisconsin and Illinois. Though it has been found in areas west of this line, it has not yet reached population numbers that cause widespread concern at this time.

Ironically, the adult beetle is rather attractive. The half inch body is basically iridescent green, with the wing cases being coppery in color. There are two white spots on each end of the abdomen with five more along each side.

Sometimes 50 to 100 males and females will ball together in a mating orgy, and after fertilization, a female will lay three or four eggs in the soil. This will continue for about a month with a total of about 50 eggs being produced during her lifetime. The eggs hatch into tiny larvae or grubs, which immediately go to work feeding on the roots of grasses and other plants. The grubs are perhaps the most destructive insects of grass and other plants on golf courses, pastures, cemeteries, parks, and home lawns.

In late autumn, the grubs are mature and dig deeper into the soil to pass the winter. They become active and move to the surface and resume feeding as soon as the soil warms in the spring. A quiescent or pupal stage follows, allowing the adult form to metamorphose. The adults start emerging in the Rock River Valley about the middle of July and start to feed voraciously on more than 250 species of plants. From casual observations of beetle numbers I made last year, a smaller-than-normal population was indicated, so we should not expect a massive number of them this year, but even a few are too many.

They attack the leaves of broad-leafed plants, skeletonizing them by leaving only the veins of the leaf intact. If the destruction of leaves is massive, the plant is weakened and may die.

Japanese beetles are difficult to control. The now-banned chlorinated hydrocarbon type of potent insecticides did a fair job killing them in the past, but these dangerous chemicals are no longer available to the general public. For a list of chemical insecticides currently approved for Japanese beetle control, the extension agent should be consulted.

Several other methods of control, however, are available to the homeowner. The laborious task of removing the beetles by hand and putting them in soapy water to kill them is one, and the distribution of a powder of the bacterium that causes milky disease in the insects and eventually does them in is another. The powder is not toxic to humans. The use of one organism to control another is called biological control, and the use of microscopic roundworms called nematodes has been partially successfully in the past to control this beetle.

A pheromone-type sex attractant combined in a plastic trap is available in most garden shops and will entice great numbers of Japanese beetles to their doom. This agent is an air-borne sex hormone and attracts beetles to its source. Though many will be caught in the trap, many more will not. Those that avoid the trap will set up housekeeping in the immediate vicinity and add to the homeowner’s problems.

I encourage others to use the pheromone traps, but I never employ one in my own yard, for obvious reasons.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

from the Aug 1-7, 2007, issue

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