Quantification of the impact of hoverflies (Diptera: Syrphidae) on cereal aphids in winter wheat: an analysis of field populations.
Abstract
An analysis of predation of cereal aphids (Sitobion avenae and Metopolophium dirhodum) by larvae of Episyrphus balteatus is described. Field data on the absolute densities of predator and prey in winter wheat crops in Sussex, southern England, in 1981 and 1982 were used. Two quantities were calculated and compared: the estimated kill rate by syrphid larvae and the kill required to provide the degree of control observed in the aphid population. This approach provided a separate analysis for each weekly sampling interval to identify when predation was most effective, and permitted an initial appraisal of the impact of other antagonists acting concurrently. The method indicates clearly if syrphids were sufficiently numerous to achieve control alone or, alternatively, if they were too few to have had any significant effect on the aphid population. Syrphid larvae had the potential to halt the aphid increase in 4 of the 6 field populations analysed.