Prey availability and abiotic requirements of immature stages of the aphid predator Sphaerophoria rueppellii

Abstract

Aphidophagous hoverflies (Diptera: Syrphidae) are natural enemies with a high potential as biological control agents. Nevertheless, there is only one commercially available species, Episyrphus balteatus, which despite naturally occurring in the Mediterranean basin, is not the best adapted to the conditions found in its agricultural areas. Sphaerophoria rueppellii is another common hoverfly species in the Mediterranean area both in outdoor and greenhouse crops. However, little information about the biology of this species is known and this is one of the main requirements for every control-based IPM program. In this work we assess the influence of different humidity and temperature combinations on the performance (mortality, developmental time and sublethal effects) of S. rueppellii under controlled conditions. We also study the effect of aphid supply during larval stage on mortality and developmental time of immature stages and on sublethal effects on adults. The results show that this species requires high environmental humidity (higher than 60%) to complete its development. Also, S. rueppellii is able to properly develop at a wide range of temperatures (20–30 °C). S. rueppellii reduces its voracity under low aphid density conditions, being able to adapt its feeding rate to the aphid availability. Mortality was not affected by food supply, while low prey availability led to longer developmental time and a decrease in larval and pupal weight and adult body size. These results show the suitability of this species as an aphid biological control agent under high humidity and temperature conditions, such as the ones inside Mediterranean greenhouses.