When the stock is grown in the field in uncertified plots, the infestation may be destroyed by immersing the roots in water at a temperature of 112 , or by dipping the roots in dilute emulsions of carbon disulfide, ethylene dichloride, or ethylene dibromide-ethylene dichloride, or by fumigating them with methyl bromide in a closed chamber.

The use of these methods by nurserymen and others for treating fruits, vegetables, and nursery stock to satisfy the requirements of the quarantine because of the Japanese beetle is discussed in more detail in the chapter "Off Limits for Beetles," page 574.

The fact that the beetle, although common in Japan, was not a pest of much importance, suggested the existence of insect or other enemies which kept it under control. A search for enemies of the beetle in Japan and elsewhere was carried on from 1920 through 1933. It was found that a relatively large number of insect parasites and predators attacked the various stages of the Japanese beetle and related species. About 49 species of insect parasites and predators were shipped to the Department's laboratory in New Jersey from Japan, Korea, Formosa, China, India, Australia, and Hawaii. Some parasites were released immediately in the beetle-infested area. Others were used for further study or reared to provide additional parasites for subsequent release.

Five species of imported insect parasites have become established in the beetle-infested area. Two of these, the spring Tiphia (Tiphia vernalis) from Korea and the summer or fall Tiphia (Tiphia popilliavora) from Japan, are well established and are one of the important causes of a decline in Japanese beetle numbers in the older infested area. Both parasites are wasps that attack the grub of the Japanese beetle. The wasp lays an egg on the body of the grub. The maggot that hatches from the egg feeds on the grub and destroys it. The first colonies of the spring Tiphia were released in 1926 in New Jersey; by 1951 a total of 2,018 colonies had been released in 14 States from New Hampshire to North Carolina and westward to Ohio. State authorities, using wasps collected locally from the sites of earlier releases made by the Department, released several hundred additional colonies. The fall Tiphia was first released in 1921 in New Jersey; by 1951, 767 colonies were released in nine States.

Surveys were made between 1935 and 1951 to determine the distribution of the spring Tiphia. By the close of the 1951 season the parasite was generally distributed over an area of some 5,300 square miles in eastern Pennsylvania, Delaware, and southern New Jersey. It also occurred at many scattered points in the beetle-infested territory outside of this area. Because the wasp attacks only the grub stage of the beetle in the ground, any estimate of the effectiveness of the parasite must be based upon the actual number of parasitized grubs in proportion to the total number of all stages of the beetle found in the ground at the time of the survey. The surveys disclosed a range of parasitization from 19 to 61 percent, with a general average of about 43 percent. The spring Tiphia is the most effective of the introduced insect parasites of the beetle, but the other established parasites are also contributing to the reduction of the beetle population.

The native insect parasites and predators of white grubs occurring in the area infested by the Japanese beetle have been studied to find out to what extent they attack the beetle. Occasionally grubs have been found parasitized by native Tiphia wasps. A species of Ptilodexia, a fly known as a parasite of white grubs, was found attacking Japanese beetle grubs to an extent that suggested that it may ultimately be of importance in biological control. With this exception native parasites and predators appear to play at best only a minor part in the control of the beetle.

Early observations indicated that the grubs were subject to several diseases. About 25 different soil microorganisms can cause some stage of the Japanese beetle to become diseased. Among these are bacteria, fungi, protozoa, nematodes, and viruses. The bacteria causing the milky diseases of the Japanese beetle grubs were found to be the most important of the organisms. These are spore-forming bacteria, Bacillus popilliae and B. lentimorbus. The former, the more important, causes the type-A milky disease. A more complete discussion of the milky disease begins on page 394.

Another disease found in Japanese beetle grubs is the blue disease, so-called because of the bluish tint of infected grubs. Its causal organism is believed to be a virus. The disease seems to be very potent and may lend itself to large-scale utilization in much the same manner as the milky disease.

Several species of nematodes, tiny microscopic worms commonly found in the soil, cause considerable mortality among the grubs and are an important factor in biological control. Their effectiveness depends much more on favorable climatic and soil conditions than do the milky diseases, however.

Several species of fungi attack the Japanese beetle. The most important is the green muscardine fungus, Metarrihizium amsopliae. It is widespread and under favorable conditions is important in the biological control of the beetle.

CHARLES H. HADLEY was an entomologist in the division of fruit insect investigations of the Bureau of Entomology and Plant Quarantine. He was in charge of Japanese beetle investigations, with headquarters at the Japanese Beetle Research Laboratory at Moorestown, N. J., until he retired in 1952.

WALTER E. FLEMING is also an entomologist. He succeeded Mr. Hadley at Moorestown and is in charge of the station.