With resistance of insect pests to synthetic pesticides on the increase, the role of parasitoid wasps as biological control agents is expanding in pest and resistance management strategies. One of the predictors of reproductive success of endoparasitoids is the relative size of the wasp at host emergence. While in idiobiont parasitoids, where the host stops feeding after parasitism, the wasp size is determined by the host size at the time of parasitism; the size of koinobiont wasps, where the host continues to feed after parasitism, is dependent on additional factors. Here we show that the host mass and temperature are important factors that determine survival and development of the koinobiont endoparasitoid Venturia canescens in late instar larvae of the flour moth Ephestia kuehniella.