Stable flies, Stomoxys calcitrans L. (Diptera: Muscidae), improve offspring fitness by avoiding oviposition substrates with competitors or parasites.

Oviposition site selection by gravid female insects is an important determinant inspecies distribution, abundance, and population dynamics. Females may assess thesuitability of a potential oviposition substrate by using cues from conspecific orheterospecific individuals already present. Here, we assessed whether the presenceof conspecific or heterospecific larvae and parasites influenced oviposition decisionsby the stable fly,Stomoxys calcitrans(Linneaus). Using dual and multiple-choiceoviposition bioassays, we found that gravid femaleS. calcitransavoided substrates withconspecific larvae, the larvae of house flies,Musca domestica(Linneaus), and the miteMacrocheles muscaedomesticae(Scopoli). Avoidance of conspecific and heterospecificlarvae persisted in the dark, suggesting that this behavioris mediated by chemicalrather than visual cues. When we rearedS. calcitransin the presence of conspecificlarvae and the larvae of house flies at different densities wefound that this negativelyaffected emergence time, larval weight, larval survival, pupal weight, pupal survival, andadult weight. We also demonstrated that individuals ofS. calcitransdeveloped in thepresence of mites exhibited low egg hatchability, and poor larval and adult survival.Our study provides additional support for the “preference-performance” hypothesis inS. calcitrans, with gravid females preferring to lay eggs on a substrate that will enhanceoffspring fitness. We recommend that the chemical cues involved in avoidance by gravidfemaleS. calcitransof substrates with conspecific and heterospecific larvae shouldbe elucidated. This could lead to the discovery of repellentchemicals important forS. calcitransmanagement