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Large-scale aerial applications of chemical insecticides against spruce budworm (Choristoneura fumiferana (clem.)) took place in Quebec during two outbreaks, 1952-58 (Outbreak I) and 1970-75 and continuing (Outbreak II), in an effort to prevent extensive mortality of fir and spruce. During Outbreak I yearly treatment consisted of one application of DDT at 0.6 kg/ha (8 oz./ac.); during Outbreak II it consisted of two applications of organophosphates and carbamates (mostly fenitrothion) for a total of 0.3 kg/ha (4 oz./ac.). The effects of a single treatment were evident for two years in Outbreak I because of residual properties of DDT, while in Outbreak II, effects were evident only in the year of application. Reduction in budworm populations due to treatment was considerably greater during Outbreak I than during Outbreak II. Average foliage protection in the year of treatment and in the following year was 38% and 60% respectively in Outbreak I, while it was 15% and 0% in Outbreak II. Spray operations in any one treatment area were repeated after an interval of three or four years due to population build up in Outbreak I; continuously high populations necessitated yearly applications of insecticides in Outbreak II. It is suggested that the current spraying policy in Quebec should be reappraised in the light of conditions that prevail.

Comparative Appraisal of Insecticidal Operations Against Spruce Budworm in Quebec During Two Outbreaks