In August 1941, the grub count in soil surveys made at seven treated places averaged 31.5 per square foot. By June 1942 the count at the same places was 7.0 per square foot; 12 to 70 percent of the larvae were milky. Information is also available from surveys made at i o widely scattered places twice each year from 1946 through 1949. The grub population at those places averaged 5.0 in June 1947, 5.4 in June 1948, and 1.6 in June 1949. The disease incidence at the time of the surveys averaged 46.o percent in 1947, 45.5 percent in 1948, and 57.0 percent in 1949. There has been a noticeable reduction in beetles in the District in recent years, as would be expected from the low grub populations, despite weather conditions that favored an increase in numbers. Surveys made in 1948 at several points where no spore dust had been applied showed the disease to be present at all of them. Milky disease probably occurs to some extent wherever there are grubs in this area. The Japanese beetle was present in great numbers in 1951 in places a short distance from the District bf Columbia; it was believed that the low populations in most parts of the District could be attributed largely to the high incidence of milky disease there.

THE MORE GRUBS there are to the square foot the faster the disease becomes established and the more rapid the spread. There had been high grub populations in the three locations I have described and the number of disease spores in the soil had become large. Grubs will usually be plentiful in a place where there are many favored food plants on which the beetles can feed and plenty of good turf for egg laying. This was the case at all the places where disease activity has been described. If the conditions are less favorable, there will be fewer beetles, grub populations will be lower, and it will take longer to build up effective numbers of spores in the soil. There-Fore, the situation may not always be so favorable as in the instances given. In order to get the disease established as soon as possible, spore dust has sometimes been introduced where the grub population was as low as one or two per square foot. The build-up of disease in such places is likely to be slow. Under highly favorable conditions, pod establishment of the disease has wen obtained by the second season after introduction. A longer time has wen required in less favorable situations.

SINCE THE SPORES can survive under adverse weather conditions, the dust will not have to be reintroduced once he disease has become established in he grub population. Even though unfavorable weather conditions have sometimes reduced grub populations to as low as one grub per square foot, the disease still persisted and became active again as the grub count rose. In some newly colonized places, milky disease is not yet so effective as it eventually will be because of the time ceded for it to become generally established. Because of lower temperatures in the northern part of the beetle-infested area, some observers feel that a longer time will be required for the disease to become established there than in warmer places to the south. However, we have every indication that the disease can become established wherever the beetle exists.

Because of the time needed for effective build-up, the use of the disease as an immediate control measure is not advised in situations where beetle grubs are so numerous that turf is being injured. A rapidly acting poison should be used to kill the grubs and protect the grass. The poison will not kill any spores that are present. Spore dust, applied at a heavy dosage to such places, has reduced the number of grubs and checked the injury, but not always in time to prevent additional damage to the grass.

Milky disease organisms probably occurred in our native white grubs before the Japanese beetle was introduced into this country. When the type-A disease was first found in grubs of the Japanese beetle, grubs of many of our native species of May beetles, or June beetles, were examined closely and disease was found in several of them. Apparently several kinds of bacteria caused milky diseases in different kinds of white grubs. The type-A organism may have existed in some of the native grubs and then, with the arrival of the Japanese beetle, found its grubs favorable to its development. As far as we know, only certain species of white grubs develop the milky disease. We have no records of a condition just like it in other insects.

MY DISCUSSION has dealt largely with the important type-A organism because it is the one usually found in field-colonizing work. Another organism sometimes found in grubs of the Japanese beetle is Bacillus lentimorbus, which causes the type-B milky disease. Attempts to produce the spore form of this organism in artificial culture, as with type A, have been unsuccessful. Spore dust made of the type-B organism has been tested in field plots, but the results obtained were not so good as those with type A.

BESIDES THE MILKY DISEASE, many biological agents destroy beetle grubs other bacteria, parasitic fungi, nematodes, parasitic and predaceous insects, birds, and other animals. The amount of summer rainfall is an important factor, for beetles are always reduced in number following summers with low rainfall. Among all of these factors, the milky disease is perhaps the most effective in checking the build-up of the Japanese beetle, as it spreads into new areas, mostly free from its natural enemies. Any agent that slows down or checks this initial build-up makes the pest less destructive. The milky disease is such an agent and this is the reason for colonizing it in newly infested places as soon as the grub population reaches the point where it will support the disease. Diseased spores will then increase in numbers in the soil as more and more beetle grubs become diseased. The number of beetles will decrease again and the Japanese beetle will cease to be the serious pest it has been.

IRA M. HAWLEY is a native of New York State and a graduate of the University of Michigan. He has a doctor's degree from Cornell University. From 1931 to 1952 he was in charge of biological studies of the Japanese beetle. Dr. Hawley's special interest has been in the seasonal cycle of the insect in different parts of the infested area, its reaction to weather conditions, and its spread and abundance from year to year. He retired in 1952.