Oviposition preference of two hoverfly species in response to risk of intraguild predation

Two experiments were performed in the laboratory to understand the relationships between oviposition preference and larval performance of the two predatory hoverfly species, Episyrphus balteatus de Geer and Metasyrphus corollae Fabricius. We first conducted laboratory experiments to understand the nature and relative strengths of intraguild predation between the larvae of three ladybird species, Harmonia axyridis Pallas, Propylea japonica Thunberg, and Scymnus posticalis Sicard, and two predatory hoverfly species. The interactions between larvae of the three ladybird and two hoverfly species differed depending on the species and developmental stages involved: the relationships between H. axyridis or S. posticalis and the two hoverfly larvae tended to be asymmetric with H. axyridis being a superior species and S. posticalis an inferior species, although the reverse was true for each of these two species when small larvae were paired with large larvae of the hoverflies. The ladybird, P. japonica, had both asymmetric and symmetric relationships depending on the hoverfly species with which it interacted. Secondly, we tested the preference and performance hypothesis for hoverflies, by determining whether hoverfly oviposition preference was related to the risk of intraguild predation posed by the presence of a ladybird larva in an aphid colony. Oviposition preference in relation to larval performance of the two hoverflies differed between the species: E. balteatus females tended to adjust their rate of eggs laying in response to the presence of ladybird larvae, while similar responses of M. corollae females were weak. The relationship between oviposition preference and larval performance in hoverflies is discussed.