THE SPRUCE BUDWORM

R. C. BROWN, H. J. MACALONEY, P. B. DOWDEN.

The spruce budworm is a small, foliage-feeding caterpillar that periodically kills an immense amount of spruce and balsam fir in the Eastern States and Canada. It is serious in jack pine in the Lake States, and in Douglas-fir, alpine fir, white fir, Engelmann spruce, blue spruce, lodgepole pine, and ponderosa pine in the West.

It is native to North America. Records of its ravages in the East date from about 1805. It appeared again in epidemic proportions about 1880.

The first outbreak to be studied carefully began in Quebec in 1909, appeared in Maine in 1910 and in New Brunswick and Minnesota in 1913, continued for nearly a decade, and destroyed more than 250 million cords of spruce and fir pulpwood. About 30 million cords were killed in Maine; in Minnesota, more than 20 million cords were destroyed.

But all that devastation, all that destruction may be nothing compared to a current outbreak in Canada that began to assume epidemic proportions in 1935. By 1944, it was estimated, 125 million acres in Ontario were infested. In 1945, an official of a Canadian pulp and paper company said, the insect killed enough timber to supply all Canadian pulp mills for 3 years. By 1947 most of the mature fir and a considerable part of the white spruce on an estimated 20,000 square miles had been killed, with less intense damage over a much larger area. The dead trees have created a tremendous fire hazard; large areas affected by the budworm already have been burned.

The memory of the previous outbreak in Maine and the present situation in Canada have caused great alarm among owners of timberland and officials of the pulp and paper industry in the Northeast. At stake in the region are nearly 19 million acres of spruce-fir and more than 100 million cords of pulpwood. On that timber supply depend more than 90 mills, which have an annual capacity of 3Y2 million cords, employ more than 55,000 workers, and manufacture goods worth more than 300 million dollars annually.

BECAUSE OF THE SERIOUS THREAT to the pulp and paper industry, the timberland owners asked Congress for funds to find ways to control the insect and to prevent widespread damage such as had occurred in Canada. The funds were voted, and in July 1944, two units of the Department of Agriculture, the Bureau of Entomology and Plant Quarantine and the Forest Service, began a program to study the problem in all its phases and develop a plan of action for the Northeast. Surveys in which the States cooperated indicated that few specimens of the spruce bud-worm were present then in New England forests.

But in 1945 we discovered an infestation in the Adirondacks of New York. The next year we found many more, and an outbreak seemed imminent. In 1947 and 1948, however, the population of spruce budworm dropped markedly. Over most of the area, defoliation was not severe enough to cause appreciable damage to spruce and fir. During 1945, 1946, and 1947, the insect remained at an extremely low population level in Vermont, New Hampshire, and Maine. The 1948 survey showed a low degree of abundance in Vermont and New Hampshire but a definite increase in Maine. No report of unusual abundance of the budworm has been received from the Lake States. Extensive outbreaks were in progress in 1948 in the southern, central, and northern Rocky Mountain regions and in Oregon and Washington.

From 1945 to 1948 intensive studies in biological and natural control of the insect were conducted in New York. Plots and experimental areas were established in the Northeast to determine the degree of defoliation and damage caused under different forest conditions. In the Rocky Mountains there are several species of parasites of the budworm that do not occur in the East; several colonies of those parasites were obtained and released in eastern forests in the hope that they would become established.

THE SPRUCE-FIR STANDS in the Adirondacks, relatively small in area, usually are surrounded by hardwoods. Such stands seem particularly favorable for natural control. Winter mortality during 1946-47 was approximately 75 percent. Aggregate parasitization by insect enemies ranged from 64 to 86 percent in different area. The total aggregate mortality from winterkill and parasites ranged from 83 to 98 percent. Insectivorous birds also destroyed large numbers of budworm larvae and pupae. Certainly those factors of natural control contributed tremendously in bringing about the decline in budworm infestation in 1947 in New York.

THE SEASONAL HISTORY of a pest must be known before control measures can be undertaken.

The adult of the spruce budworm is a small moth with a wing spread of seven-eighths of an inch. Its general color is grayish with brown markings.

In the Northeastern States the moths start emerging from their pupal cases about July 1. The females deposit their pale-green eggs on the foliage in masses of 10 to 50 or more, where they overlap like the scales of a fish. One female may lay several of these egg masses and on the average produces about 175 eggs. The incubation period lasts about 10 days.

After the eggs hatch, the young caterpillars crawl about until they find suitable places under bark or bud scales to spin silken weblike coverings, or hibernacula,under which they spend the following fall and winter. These tiny larvae do not feed until they become active in late April or early May and leave their hibernacula. At first they are an orange yellow; later they turn brownish. They mine the old needles first; then they enter the opening buds, where they feed on the tender young needles which are just starting growth. They also feed on spruce and fir pollen. As the new shoots elongate, the larvae tie the needles together with silken threads and thus form shelters within which they feed. By late June they are full-grown, reddish brown in color, and start forming the pupal cases, which are attached to the twigs. The pupal period lasts 7 to 10 days, after which the moths emerge and start laying eggs a new generation is under way.

The spruce budworm may spread over long distances to new areas by flights of the moths. Records of the 1910-19 outbreak show that in July 1911 swarms of moths appeared in Philadelphia and in 1912 and 1913 they were abundant in Connecticut. Those localities are outside the general spruce-fir range, so the presence of the moths there had significance only in showing how far they travel.

The regions where extensive tree mortality has already occurred in the present outbreak and the extent of the active infestations are shown on the accompanying map. There is no record of a flight of moths in 1944 from Canada that might have caused the outbreak conditions discovered in New York in 1945. Apparently, though, a heavy infestation arose simultaneously over an area of approximately 3,000 square miles, and careful study of the area in 1945 pointed strongly to the possibility of a widespread flight of moths in 1944.