Temperature influences the handling efficiency of an aphid parasitoid through body size-mediated effects

It is well known that increasing the ambient temperature increases the metabolic rate and consequently, the foraging rate of most insects. However, temperature experienced during the immature stages of insects affects their adult size (an inverse relationship). Because body size is generally correlated to foraging success, we hypothesized that temperature indirectly inßuences the foraging efÞciency of adult insects through developmental effects. We Þrst investigated the role of parasitoid: host body size ratio on the handling time of Aphidius colemani (Viereck) (Hymenoptera: Braconidae), then tested the prediction that increasing temperature during immature development increases the handling time of adults. As expected, parasitoids took longer to handle large aphids than small aphids. However, large parasitoids did not have shorter handling times than small parasitoids except when attacking large (adult) aphids. Developmental temperature had the predicted effect on parasitoids: Individuals reared at 25ЊC were smaller than those insects reared at 15ЊC. Parasitoids reared at 15ЊC had similar short handling times for both Þrst instar and adult aphids, whereas parasitoids reared at 25ЊC took longer to handle adult aphids than Þrst instar aphids. The size-mediated effect of temperature through development on parasitoid efÞciency was opposite to the more familiar direct effect of temperature through metabolic rate. We conclude that the net effect of temperature on foraging insects will depend on its relative inßuence on immature and adult stages.