Syrphid aphidophagous predators in a food-web context

The main influences on the specificity of hoverfly larvae (Diptera: Syrphidae) to particular aphids are outlined. There are four main ones: aphid species, host plant, parasitoid impact and the presence of ants. Studies in the literature are used to illustrate the effect of these factors on larval performance. The use of single components of fitness as measures of performance can be misleading: only individual fitness includes all the appropriate components of survival, development time and reproduction. Even generalists appear to choose among aphids on the basis of expected fitness. A new level of complexity is therefore required in studies of food specificity in predatory syrphids.