Oviposition and host foraging cues of stable flies (Stomoxys calcitrans), and their potential as vectors of microbial host pathogens

Stable flies, Stomoxys calcitrans, are blood-feeding ectoparasitic pests of cattle. I studied mechanisms that underlie oviposition and host foraging behaviour of stable flies and investigated whether they transmit pathogens. I show that odor and moisture of oviposition sites play distinguishable functional roles in the close-range attraction of gravid flies and their propensity to oviposit, and that ammonia – alone or with carbon dioxide – attracts flies and induces oviposition. I further show that several Staphylococcus microbes in the bovine skin microbiome attract host-foraging flies, and that ammonia and odorants emitted by these Staphylococcus microbes attract flies. Finally, I show that stable flies are attracted to the skin-dwelling, mastitis-causing bacterium Staphylococcus aureus, and that they transmit S. aureus from infected blood to sterile blood. My data infer the existence of a positive feedback loop. As S. aureus bacteria of afflicted cows proliferate, they attract even more flies which, in turn, worsen the infection.