Predatory hoverflies increase oviposition in response to colour stimuli offering no reward: Implications for biological control

Abstract

There are increasing efforts worldwide to engineer agroecosystems to enhance ecosystem services such as carbon storage, minimisation of erosion, and biological control of pests. A key group of insect biological control agents is the hoverflies (Diptera: Syrphidae). While adult Syrphidae are pollen and nectar feeders, the larvae of many species are aphidophagous, thus demonstrating life-history omnivory and their potentially important role in the biological control of aphids and other pests. Several experiments have been conducted to assess whether the presence of flowers in or near crops has an effect on oviposition by syrphids, but the results have often been inconclusive. This paper describes a large-scale field experiment carried out over two years, in which standardised model flowers were placed in field margins and oviposition rates monitored near them. Statistically significantly more eggs were laid on broad bean (Vicia faba) infested with the pea aphid, Acyrthosiphon pisum, near yellow model flowers with and without pollen and honey resources than at positions with no model flowers nearby. These results suggest strongly that the presence of model flowers increases hoverfly oviposition and that colour may be more important than food resources in enhancing this behaviour. This work indicates that biological control of pests by hoverflies can be enhanced by simple, non-floral agroecological interventions.