Aphid suitability and its relationship to oviposition preference in predatory hoverflies.

1. The fitness consequences of feeding on different aphids (apple, blackberry, dock, elder, nettle, pea, rose and sycamore aphids) for two species of generalist insect predator (the aphidophagous larvae of Episyrphus balteatus and Syrphus ribesii- Diptera:Syrphidae) were measured in the laboratory. The relevant literature studies on prey specialization in the Syrphidae were summarized for the first time. 2. Both the literature evidence reviewed and the data from the experiment indicated that fitness components and overall individual fitnesses are broadly similar among all aphid species, with some exceptions. 3. We correlated individual fitness to two estimates of oviposition preference, an indirect (field distribution of larvae) and a direct measure (egg distribution under laboratory conditions). In the non-resident, migratory E. balteatus significant correlations were absent, but there were indications of a weak preference-performance correlation in the largely resident S. ribesii.