The selection of oviposition sites by aphidophagous insects is complex because of tritrophic interactions among host plant, aphid, and natural enemies. Several factors are known to affect the choice of oviposition site by aphidophagous hoverflies. The decisions of ovipositing females about where to lay their eggs are even more important in insects whose newly hatched offspring have limited dispersal ability, such as most aphidophages. In this study, we focused on the oviposition responses of two generalist aphidophagous syrphids (Eupeodes luniger and Episyrphus balteatus) toward host plant–aphid combinations differing in sinigrin content and the presence of intra- and interspecific competitors. The oviposition preference of Eupeodes luniger was significantly influenced in a reverse manner by the presence of intraguild competitors and also by the sinigrin content of host plants (P b 0.0001 for both factors). Likewise, the overall proportion of eggs laid by female Episyrphus balteatus was greater on aphids with relatively low levels of sinigrin. Our findings help in understanding the factors governing the oviposition responses of aphidophagous predators.

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