A TECHNIQUE FOR ESTIMATING THE FECUNDITY OF NATURAL POPULATIONS OF THE SPRUCE BUDWORM
In a severe infestation late-instar spruce budworm larvae that normally feed on current foliage may be forced to complete development on old foliage. This results in a reduction in fecundity. The precise causes of this reduction are not known, but factors that may be involved are the amount and the age of the old foliage consumed. The relationship of pupal case size and fecundity is used as a basis for estimating the expected fecundity in a natural population under these conditions of partial larval starvation. Three regression equations applicable to conditions on the Green River area, New Brunswick, are presented. An index of the actual increase of a population is obtained from an E/F ratio. Ratios may be compared in order to indicate some aspects of oviposition. Actual and expected egg populations can also be compared, subject to certain limitations, to indicate some aspects of adult dispersal. The mean number of eggs per mass in relation to degree of infestation and a simplified method of counting eggs per mass are also discussed.