Abstract
Parasitized cabbage aphids,Brevicoryne brassicae(Linnaeus), produced fewer offspring than unparasitized aphids. Aphids parasitized byDiaeretiella rapae(M'Intosh) during the first, second, or third instar died before producing any offspring; those parasitized during the fourth instar or the adult stage produced a variable number of offspring. The aphid's survival time was correlated with the rate of development, as measured by the length of the pre-reproductive period. A multiple-linear-regression equation is provided for predicting the mean total fecundity of parasitized cabbage aphids from the host age at the beginning of parasitism and the pre-reproductive period.