The physiology of host feeding in parasitic wasps: implications for survival

1. Models developed to predict behavioural and life-history decisions of parasitoids rely heavily on assumptions concerning the nature and function of the nutrients that the female obtains from the host. 2. Using a combination of colorimetric and thin-layer chromatography techniques, we analysed the composition of the host-feeding fluid consumed by the parasitoid Eupelmus vuilletti and found it to be consistent with the composition of the host’s haemolymph. 3. The analysis of the haemolymph revealed that it was rich in proteins but also rich in sugars, trehalose and sucrose in particular. 4. Injections of these sugars at haemolymph concentrations directly into the parasitoid’s haemolymph showed that these sugars are solely responsible for the increased longevity observed in host-fed females. 5. This study is the first to identify the constituents of host-feeding meals and their impact on parasitoid longevity and provide further evidence of the extent to which parasitoid behavioural decisions are determined by physiological variables. Our study demonstrates that the integration of nutritional physiology, behaviour, life history and population dynamics is essential in order to understand parasitoid foraging ecology.