More than half of the 800 species of European hoverflies belong to the Syrphinae subfamily.  Adults feed on pollen and nectar collected in open corollae of numerous plants.  Conversely, larvae of most Syrphinae species exploit a restricted number of prey, mainly aphids.  These prey are usually well defended against predators.  We assumed that syrphid-aphid relationships result from a long coevolution and that ecological and life-history traits of the former are constrained by those of the latter.

The majority of Syrphinae species are forest dwellers and specialize on the exploitation of tree aphids.  These prey are large, move quickly and live in small, scattered but long-lived colonies.  Forest syrphids have a low fecundity but produce large eggs and neonate larvae which display high resistance to starvation, searching ability and capture efficiency.  Conversely, Syrphinae communities encountered in farmlands are less diversified.  They include polyphagous and plurivoltine species that fly over long distances and are widely distributed across the Palearctic region.  These generalist and “vagrant” species are adapted to survive in ephemeral environments, where larval mortality is high and unpredictable.  They produce a large number of small eggs and have voracious larvae that develop in a short period of time.  These life-history traits allow them to have a strong numerical response to aphid densities and to be efficient biocontrol agents.