Abiotic characteristics and organic constituents of oviposition sites as oviposition attractants and stimulants for gravid female stable flies, Stomoxys calcitrans

Gravid female stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae), oviposit in many types of organic substrates, including animal feces, but there is limited information as to which factors mediate attraction and oviposition. Here, we (1) tested effects of oviposition site moisture and odor on attraction and oviposition by flies, and (2) selected a highly effective oviposition site (fly rearing medium) to determine the key constituent(s) that mediate(s) attraction and oviposition. In moving- and still-air olfactometers as well as large laboratory rooms, we show that (1) odor and moisture of oviposition sites play distinguishable functional roles in the close-range attraction of gravid female flies and their propensity to oviposit, (2) rearing medium containing fish food, wheat bran, wood chips, and a watery solution of ammonium bicarbonate [(NH4)HCO3, releasing NH3 and CO2] is a more appealing oviposition site to female flies than is cow feces, (3) ammonium bicarbonate in this medium is the key constituent for stable fly attraction and oviposition, (4) NH3 alone or in combination with CO2, but not CO2 alone, attracts stable flies and induces oviposition, and (5) NH3/CO2 and fish food in combination are more attractive than NH3/CO2 or fish food alone. With fecal bacteria reportedly emitting NH3, and with stable fly larval development reportedly reliant on (fecal) microbes, it follows that gravid female flies may be guided by airborne microbe-derived cues originating from prospective oviposition sites. Isolating these microbes and identifying their odorants could enable the development of a synthetic odor blend which, coupled with NH3 and CO2, may prove highly effective as a trap lure to capture gravid female stable flies.