Predicting Number of Oocytes in Adult Western Spruce Budworm, Choristoneura occidentalis (Lepidoptera: Tortricidae)

Abstract

Regression equations to predict number of oocytes, or potential fecundity, of western spruce budworm (WSBW), Choristoneura occidentalis Freeman, adult females based on pupal and adult parameters are presented. Fresh pupal mass was the most precise predictor variable, pupal abdomen width and dry mass of adults or adult abdomens were less precise but still very good predictors, and pupal abdomen length was the least precise parameter for estimating number of oocytes. WSBW pupal mass decreased as the pupa aged. Therefore, it is important to know pupal age if pupal mass is used to predict number of oocytes. Duration of pupal period and pupal mass were inversely related; individuals that spent 10 d in the pupal stage were significantly smaller than pupae that developed in 7–9 d. Host species the WSBW larva fed upon significantly affected the regression between number of oocytes and pupal mass, and also affected pupal mass, adult abdomen mass, and adult whole mass but did not affect number of oocytes in the adult. Factors to consider when using pupal or adult size measurements to estimate WSBW fecundity are discussed.