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 in species distribution, abundance, and population dynamics. Females may assess the suitability of a potential oviposition substrate by using cues from conspecific or heterospecific individuals already present. Here, we assessed whether the presence of conspecific or heterospecific larvae and parasites influenced oviposition decisions by the stable fly, Stomoxys calcitrans (Linneaus). Using dual and multiple-choice oviposition bioassays, we found that gravid female S. calcitrans avoided substrates with conspecific larvae, the larvae of house flies, Musca domestica (Linneaus), and the mite Macrocheles muscaedomesticae (Scopoli). Avoidance of conspecific and heterospecific larvae persisted in the dark, suggesting that this behaviour is mediated by chemical rather than visual cues. When we reared S. calcitrans in the presence of conspecific larvae and the larvae of house flies at different densities we found that this negatively affected emergence time, larval weight, larval survival, pupal weight, pupal survival, and adult weight. We also demonstrated that individuals of S. calcitrans developed in the presence of mites exhibited low egg hatchability, and poor larval and adult survival. Our study provides additional support for the “preference-performance” hypothesis in S. calcitrans, with gravid females preferring to lay eggs on a substrate that will enhance offspring fitness. We recommend that the  chemical cues involved in avoidance by gravid female S. calcitrans of substrates with conspecific and heterospecific larvae should be elucidated. This could lead to the discovery of repellent chemicals important for S. calcitrans management.

孕雌昆虫的产卵位点选择是决定物种分布、种群丰度与种群动态的关键因素。雌虫可通过感知已存在于潜在产卵基质上的同种或异种个体释放的信号，评估该基质的适宜性。本研究以厩腐蝇（Stomoxys calcitrans Linnaeus）为研究对象，探究其产卵决策是否受同种/异种幼虫以及寄生生物存在的影响。
通过双选择与多选择产卵行为测定实验，我们发现孕雌厩腐蝇会回避含有同种幼虫、家蝇（Musca domestica Linnaeus）幼虫以及食腐螨（Macrocheles muscaedomesticae Scopoli）的产卵基质。该回避同种与异种幼虫的行为在黑暗环境中依然存在，提示该行为由化学信号而非视觉信号介导。
当我们在不同密度的同种幼虫与家蝇幼虫共存环境中饲养厩腐蝇时，发现这会显著延迟其成虫羽化时间，并降低幼虫体重、幼虫存活率、蛹重、蛹存活率以及成虫体重。此外，在食腐螨共存环境中发育的厩腐蝇个体，其卵孵化率、幼虫存活率与成虫存活率均显著下降。
本研究进一步验证了厩腐蝇中的‘偏好-表现假说’，即孕雌个体倾向于在能够提升后代适合度的基质上产卵。我们建议，后续应阐明孕雌厩腐蝇回避含有同种与异种幼虫的基质所涉及的化学信号，这有望发现用于厩腐蝇防治的高效驱避化学物质。