The Japanese Beetle

Charles H. Hadley, Walter E. Fleming.

Harry B. Weiss, who since became director of the New Jersey Division of Plant Industry, found a few shiny, metallic green beetles in a nursery near Riverton, N. J., in 1916. He did not recognize them at first, nor did anyone else, but they were finally identified as Japanese beetles, Popillia japonica. That was the first record of their occurrence in the United States. Entomological literature contained little information about them other than that they were common on the main islands of Japan and were not considered a serious pest. We knew little about their habits in Japan and nothing to indicate whether they would become serious in the United States. We did know that related beetles had caused considerable trouble in the Old World and in the other Pacific islands that they had invaded.

Apparently the beetle had come to the United States with plants before restrictions were established by the Plant Pest Act of 1912.

The adult Japanese beetle is plump, shiny brown and green with 12 white spots, and about one-half inch long. It is seen only in the summer and may feed on 275 kinds of plants.

Its white grub stage is in the ground, where it feeds on the roots of plants. The beetle does damage estimated at 10 million dollars a year to farm and orchard crops, residential and public ornamental plantings, lawns, and golf courses.

Men in the Department of Agriculture began an investigation in 1917 to get information about its development and habits in its new home. By the end of that year it was obvious that the beetle had found ideal conditions for its rapid multiplication and was capable of causing great losses to many economic crops and plants. In 1918 the Department and New Jersey authorities undertook to exterminate it, but the infestation was so well established that it could not be eradicated by the control measures then known and with the funds available.

Scientists then began work to find measures to reduce damage and prevent its spread. They set out to get full knowledge of the insect's life history and habits in its new surroundings; develop measures whereby farmers, home owners, and others could prevent material damage to crops and plants by the insect in any of its stages; develop practical and economical methods for insuring freedom from infestation of commercially grown nursery stock and agricultural products so as to prevent spread of the insect throughout the United States by the movement of those products; and to hasten natural control of the insect by the introduction and dissemination of its insect enemies from the Orient and by the practical utilization of microscopic organisms such as bacteria, fungi, and others found to attack the beetle in any stage of its growth.

Detailed information was obtained on the seasonal cycle, behavior, and reactions of the Japanese beetle to climatic conditions in both the older area of infestation and in the more recently infested northern, western, and southern areas. This information was used as a basis for the development of methods of dealing with the insect.

Each year a natural outward movement of the beetles from the margins of the area of general distribution occurs. Federal and State entomological workers make surveys each season to determine the relative abundance of the beetle in different parts of the area of general distribution.

The amount of summer rainfall is the main climatic influence on year-to-year changes in the numbers of beetles. Rainfall in June, July, and August in most of the East is normally about 12 inches. When it is below 8 inches there is such a high mortality of eggs and small grubs that beetles are less abundant the following year. A comparison of the climates in Japan and the United States indicates that the beetle probably will be able to develop in most of the States east of western Kansas. In some States farther west, summer rainfall is probably too low for survival, except in irrigated lands where adequate soil moisture is maintained. In areas where crops are grown under irrigation, no beetles would develop in nearby unwatered areas. In northern New England and some other cold parts of the country, summer temperatures may be too low for the beetle to become established. In most of the area now infested by the beetle, few die during the winter because a snow cover usually prevents soil temperatures from falling to the point where hibernating grubs would be killed. If the insect should be introduced into certain parts of the northern interior of this country, where the snowfall is normally lighter, the beetle grubs might be destroyed.

PROTECTION of fruit and foliage from attack by the adult Japanese beetle involves killing the beetles that are on the plants and keeping the beetles that fly to the plants from establishing themselves there. The Japanese beetle attacks orchard crops, small fruits, field crops, shade trees, and ornamental plants. It is a strong flier, so that during the summer there may be continuous invasions of the plantings from the surrounding infested territory. Under conditions of heavy infestation without the protection of sprays, the plants may lose all of their leaves and crop.

In the search for insecticides to control the beetle, many hundreds of materials and formulations have been tested, but only a few have given promising results. Preliminary tests with untried materials are made in the laboratory. The few promising materials found in this manner are tried on a small scale in the field and compared with one of the best sprays recommended for the protection of plants. If favorable results are obtained in the small tests, the material is used in different localities in commercial orchards, vineyards, and cornfields and is also applied to shade trees and ornamental shrubs.

Before 1943 no material had been developed that destroyed the beetles on the plants and then remained effective for several weeks. Sprays containing soap, or soap and pyrethrum, kill many of the beetles that are thoroughly wetted during the application, but the plants soon become reinfested. Repeated applications of the sprays necessary to control the beetles have injured the plants.

Whitewashing by several applications of a lime-aluminum sulfate spray before beetles become established on the plants produces a nonpoisonous coating that repels beetles in lightly or moderately infested areas. It is inadequate when the beetles are abundant. The residue from it is objectionable on ornamentals and is hard to remove from fruit at harvest.

Lead arsenate at the rate of 6 pounds to 100 gallons of water kills few beetles, but the deposit repels beetles that come to the plants later. Lead arsenate cannot be used in midsummer on peaches because of injury to the tree or on other fruits that ripen shortly after spraying because of the excess residue at harvest. A spray of 3 pounds of derris or cube to 100 gallons of water kills many beetles by contact, but the residue keeps beetles away for only 7 to 10 days. It can be used safely on all crops and ornamentals, but the period of protection it affords is short and the results vary from year to year because of the variations in the composition of the natural product.

DDT so far is the most effective material for killing beetles on plants and protecting fruit and foliage from later attack. Dusts containing DDT generally are not satisfactory because their Poor adhesive qualities require repeated applications at relatively short intervals. DDT in the form of a wettable powder or an emulsion, mixed with water at the rate of 1 pound of DDT to 100 gallons and applied by a hydraulic sprayer, will kill beetles on early-ripening apples, early-ripening peaches, cherries, nectarines, plums, and grapes and prevent the reestablishment of the insects on the plants. One application is usually enough to protect the plants until the crop is harvested. After harvest a second application may be necessary to protect new growth. A single application usually protects the foliage of fruit ripening in the late summer or early fall. One or two applications have given protection to shade trees and ornamental shrubs throughout the summer. On small plantings of corn, the injury to the developing ears can be prevented by applying the spray or by dusting with a io-percent dust when 25 percent of the ears are in silk and repeating the operation 3 days later.

Concentrated sprays of DDT applied by airplane or mist blower are effective in controlling the beetle in large acreages of corn and in large-scale spraying of shade trees and ornamentals but have not given satisfactory control in orchards. Sprays containing 1.5 pounds of DDT in the form of an emulsion or a wettable powder in 5 gallons of water have been used with no injury to the plants. Oil solutions containing 1 pound of DDT per gallon have caused some injury to the foliage of trees, shrubs, and corn.

Several chlorinated hydrocarbons and other new insecticides have been tested as substitutes for DDT since 1943. The preliminary results of tests in the laboratory and field with some of the materials are summarized. A mixture of piperonyl cyclonene, pyrethrins, rotenone, and cube resins causes temporary paralysis but kills few beetles and gives little protection to plants. Ryania, chlordane, toxaphene, aldrin, and dieldrin are of little value. Benzene hexachloride gives protection to plants for only a few days. The results with parathion and the oxygen analog of parathion were similar to those obtained with benzene hexachloride. TDE and the ethoxy analog of TDE are slightly inferior to DDT.

Methoxychlor is practically as effective as DDT in protecting orchard crops, corn, shade trees, and ornamentals. Because it is definitely less poi-serious than DDT to man and warm-blooded animals, there is an advantage in using methoxychlor on forage crops, on fruits that ripen early in the summer, and under other conditions where the use of DDT is not desirable.

POISONING THE SAP of a plant is a novel method for protecting it from attack by beetles. In preliminary tests, octamethyl pyrophosphoramide was applied in water to soil at rates up to 200 pounds per acre. The material did not injure the plants, and a sufficient amount was absorbed by them to reduce slightly the feeding by the beetles. Although the protection afforded in this preliminary test was not adequate, the method seems to have possibilities.

MANY DIFFERENT TYPES OF TRAPS have been devised, and several hundred kinds of baits have been prepared and tested. The most effective trap is one painted a primary yellow color and baited with a mixture of geraniol and eugenol or with a mixture of anethole and eugenol. Although the attractant draws beetles from the surrounding area and thereby increases the number in the immediate vicinity, it is estimated that not more than 25 percent of the beetles are captured. Traps cannot be considered a satisfactory measure for protecting plants from attack, but they are of considerable value in determining the presence of beetles in localities outside of the known infested areas. Thousands of traps are used annually by the Department of Agriculture in scouting for new infestations.