Outbreaks of the western spruce budworm in the American northern Rocky Mountain area from 1922 through 1971

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The western spruce budworm has severely damaged more than 15 million acres of publicly and privately owned coniferous forests chiefly in the American northern Rocky Mountain area. This budworm has chiefly attacked Douglas-fir, grand and subalpine firs, and Engelmann spruce; it has also attacked western larch, ponderosa pine, and western hemlock. Nearly all forests within the Northern and Intermountain Regions of the USDA Forest Service that contain these host species have been attacked sometime within the past 50 years. For about 30 years following the first reported outbreak, forest entomologists were primarily tried to learn about the biology of the budworm and the kinds and severity of damage it caused. Since 1950, they have developed sophisticated methods for surveying outbreaks, mapping their exact areas and assessing damage; they have also experimented with various chemicals in trying to control populations and thereby prevent further outbreaks. Despite availability of increasingly sophisticated devices for survey and development of several reasonably effective chemical controls, more than 5 million acres of forests are still infested; the task of control is so great that control programs have been concentrated only on areas where heavy damage has occurred or extensive tree mortality is imminent. Research on the western spruce budworm in recent years has focused chiefly on its population dynamics, behavior, genetic characteristics, and chemical control. Few investigations have been directed specifically to its relationship with the host tree species or to the patterns of its outbreaks. Such studies must be made. Fortunately, much basic information useful for these studies exists in numerous reports that document details of the chronology, geographic distribution, and general severity of many of the budworm outbreaks in the two Forest Service Regions. The general purpose of this report is to review this (mostly unpublished) information as a background for continuing biological and ecological studies of this important forest pest and as an appropriate reference for investigations into its epidemiology. Specifically, the report seeks to 1) consolidate, summarize, and present information about the location, host types, duration, effects, and measures for control applied in past outbreaks; 2) discuss factors that appear to relate to the location, duration, and probable effect of budworm outbreaks in the two Regions; and 3) identify problems for further study to more accurately assess the impact possibilities of outbreaks of the budworm in host forests managed for specific uses. Some interesting and important aspects and sidelights of past outbreaks are included for both their historical and biological significance.

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ELECTRONIC FILE - Zoology