A GEOGRAPHICAL CLINE IN EGG WEIGHTS IN CHORISTONEURA FUMIFERANA (LEPIDOPTERA: TORTRICIDAE) AND ITS SIGNIFICANCE IN POPULATION DYNAMICS

Abstract

The mean weights of the initial eggs (E_i) of the spruce budworm, Choristoneura fumiferana (Clem.), vary within and between populations. Measurements of collections from across the range of this species reveal the presence of a cline directly related to latitude and longitude of the collection source. Collection mean E_i values range from 0.219 mg in the northwest to 0.157 mg in the southeast. A similar cline, also related to latitude but negative in slope, is demonstrated for the number of eggs per unit pupal weight. This cline also finds expression in changing slope of fecundity/pupal weight regressions. The cline in egg weight appears to be an adaptation to winter conditions across the range of this insect and should be considered in population dynamics.