A Comparison of the Developmental Rates of One- and Two-Year Cycle Spruce Budworm

Abstract

The spruce budworm, Choristoneura fumiferana (Clem.), is indigenous to most of the boreal forests in Canada and adjacent Eastern and Western United States. Throughout most of this range the budworm maintains a one-year cycle, overwintering as second instar larvae. In some mountainous areas of Alberta and British Columbia, a form of the budworm has a two-year cycle and over-winters as second instar larvae in the first year and as fourth instar larvae in the second year. The habitat temperatures of these two forms were investigated and related to rates of development in an attempt to discover the environmental factor which maintains the two-year cycle budworm as a distinct form even though it is geographically surrounded by the one-year cycle budworm.