Besides study plots, special techniques have been used in Maine to determine the role of natural control factors by artificially infesting trees with known numbers of spruce bud-worms. Some trees are caged to exclude parasites and birds. This method may permit a more precise evaluation of the natural enemies of the insect.

Although the area of noticeable defoliation in Maine has increased in size since 1949, the budworm population on individual trees in the older infestations has not shown a consistent increase; in fact, there are nearly as many instances where a decrease has occurred. Undoubtedly a gigantic struggle is in progress between the spruce budworm and its natural factors of control. The next few years will determine its outcome.

SEVERAL SPECIES OF PARASITES occur in the West but not in the East. Since 1945 the parasites have been reared and shipped to the East for colonization in the Adirondacks and Maine. It is too early to determine if they have become established in eastern infestations. As far as we know, all the eastern species of parasites exist in the West.

In 1950, studies were conducted in stands of Douglas-fir and white fir in three well-separated study areas in eastern Oregon to determine the effect of natural factors in controlling the spruce budworm. Aggregate parasitization there was 61, 52, and 32 percent.

In the third area, where parasitization was low, possibly because of the complexities of retarded seasonal development, however, 60 percent of the pupae died from what appears to be a disease. Aggregate mortality observed was, therefore, 73 percent in that area. No evidence of disease was noted in the other two. That is the only known record of appreciable mortality of the spruce budworm that may possibly be attributed to disease.

Studies to determine the application of biological information to silvicultural practices are being carried out. Sample plots have been established in areas that represent a wide variety of conditions of stand and site. If defoliation becomes sufficiently heavy to injure or kill trees, detailed studies will be undertaken to determine the effect of defoliation on spruce and fir in the sample plots. Defoliation in the Adirondacks was insufficient to damage trees and thus far no appreciable injury has occurred in Maine.

To demonstrate the cutting methods that I have described, 19 experimental areas covering 50 to 750 acres each have been established by the Forest Service, the Bureau of Entomology and Plant Quarantine, the States, and timberland owners in the Northeast. They are located in different parts of the region so that the influence of stand and site conditions may be observed if a budworm outbreak should occur.

Studies have been under way since 1945 to determine effective means for controlling the budworm by the aerial application of DDT. In that year field tests were initiated in the Province of Quebec, and three small plots were sprayed in the Adirondacks. Tests were continued in New York in 1946 and 1947, in Oregon in 1948, in Maine in 1949 and 1950, and in Quebec in 1951.

Undoubtedly the spruce budworm is highly susceptible to low dosages of DDT, but because of its concealed feeding habits it is much more difficult to control than free-feeding defoliators. Some of the tests made in 1945, 1946, and 1947 gave good results, but not all were satisfactory. Applications made when the insect was in the needle-mining stage and the early bud-feeding stage did not give a high degree of control. As the caterpillars became larger and were more exposed, the percentage of mortality from the spray applications increased. During the last 2 weeks of larval development, from about June 15 to July I, many of the tests gave good control. Applications made for control of the budworm adults were ineffective. Most of the tests in the East were made in infestations of only light to medium intensity.

In 1948 a series of plots were treated with a small fixed-wing plane and a helicopter in a heavy infestation on Douglas-fir and white fir in eastern Oregon. The plots were sprayed with dosages of 1 and 2 pounds of DDT per acre during the last 2 weeks of larval development. The results were outstanding. In 10 of the 12 plots, more than 97 percent control was obtained. No appreciable difference was seen between the 1 and 2-pound dosages or between the airplane and helicopter applications. One of the two plots that gave lower control was inadvertently sprayed with a one-half pound dosage, and the other was treated late in the afternoon when thermal currents affected deposition of the spray.

The high percentage of control obtained in the tests in Oregon apparently was due largely to the extremely high larval population. The caterpillars were more active in their competition for food and were consequently more exposed than in the lighter infestations in the East, where an abundance of food was present and they were less active. The tests demonstrated that excellent control can be obtained by the aerial application of 1 pound of DDT in 1 gallon of spray per acre.

Experiments in Maine in 1949 and 1950 and in Quebec in 1951 were designed to obtain more precise information on the actual spray deposit on the foliage and the influence of such factors as droplet size and formulation of spray on deposit. The tests were made in relatively light infestations, and the control with a 1-pound dosage, measured as reduction in population, ranged from about 80 percent to more than 95 percent in the treated plots. The experiments showed that uniform coverage of the spray is a critical factor in obtaining a high measure of control. The amount of spray material, type of formulation, droplet size of the spray, weather conditions, and stand conditions are important mainly insofar as they influence the actual amount of DDT deposited on the foliage. Insuring a deposit of a lethal dosage is the primary problem of aerial application. A study of dosage-mortality relationships has shown that approximately 0-3 pound of DDT per acre is the minimum deposit for effecting go percent or more reduction of the bud-worm population in the late larval stages.

A HIGH DEGREE OF CONTROL of the budworm can be obtained but we have little information on the rapidity of build-up from the residual population left after spraying or the rate of reinfestation from the periphery of a treated area.

Spraying operations usually are carried on in the most heavily infested parts of a forest, and invariably there are more lightly infested adjacent areas that remain as a menace to the treated area. Some question exists as to the most effective time for applying treatment during the progress of an infestation. Should an area be sprayed in the early stages of infestation or should treatment be delayed until just before the time when defoliation is sufficiently severe to cause tree injury? We need to make further tests to determine the earliest stage in its life history at which the insect can be effectively controlled, with the hope that control operations may be carried out over a longer period during the season and greater protection afforded to the foliage of the current season. At present, spraying is restricted to about 2 weeks near the end of the feeding period an exceedingly short time if vast areas need to be treated. Studies are needed to determine the effect on the natural enemies of the spruce budworm of spraying large areas with DDT.

In appraising infestations, it is desirable to determine the degree of control that natural factors exert. Perhaps under some conditions the infestation is actually subsiding from the activity of natural control factors and spraying may be unnecessary. The Adirondack infestation is a case in point.

Studies to determine the effect of DDT on birds, fish, and other wildlife have been conducted since 1945. Several forested areas have been sprayed specifically for those studies, and observations have been made in other areas sprayed to control forest defoliators.

In one locality sprayed experimentally with 5 pounds of DDT per acre, a population of more than three birds to the acre declined in 2 weeks to about one-sixth of the original population. In another place, sprayed for four consecutive years at the peak of the nesting period with 2 pounds of DDT per acre, no deleterious effect on birds was evident. In all experimental tests, birds were unaffected by a single application of 1 pound of DDT per acre.

All in all, the investigations have allayed many early fears of the use of DDT in the forest.

The greatest need in the future is an expansion of studies of the natural control of the insect. Such studies should be conducted throughout the country where the spruce budworm is a threat. We should try to determine under what forest conditions natural factors will keep the insect in check and why outbreaks develop in other areas. Studies should be undertaken to determine the effect of silvicultural practices on natural control as well as the effect of the widespread application of DDT on the natural enemies of the insect. That will call for the closest cooperation between those who conduct surveys, those who carry out control operations, and those who are working on basic research problems.

R. C. BROWN is an entomologist in the Bureau of Entomology and Plant Quarantine. He was graduated from the University of New Hampshire in 1922 and has been in the Bureau since 1925. In 1935 he was put in charge of the laboratory of the division of forest insect investigations in New Haven.