Identification of Semiochemicals in the Feces of Stable Flies, Stomoxys calcitrans, that Attract Conspecific Flies.

Stable flies, Stomoxys calcitrans, are severe blood-feeding pests of cattle. As previously reported, fecal deposits of stable flies attract conspecific flies. Here we report the identification and behavioral testing of fly fecal semiochemicals. In laboratory two-choice bioassays, CO2-activated flies landed more often on sites baited with stable fly feces, or water extract thereof, than on unbaited control sites. Water extracts of feces attracted flies, whereas non-polar solvent extracts did not. Fecal deposits only of blood-fed, but not sugar-fed, flies elicited preferential responses, indicating that the feces-derived semiochemicals are metabolites of blood protein digestion. Analyses of freeze-dried, purified water extract - following derivatization of polar compounds - by gas chromatography-mass spectrometry revealed 13 polar candidate semiochemicals. A synthetic blend of formamide, ethylamine, ammonium carbonate, urea, valine, 3-methylbutyric acid, lactic acid, ketoisocaproic acid, and oxalic acid attracted flies as effectively as water extract of feces, but not all constituents of this synthetic lure may be needed for fly attraction. Further research is needed to determine whether the synthetic blend attracts flies in field settings, and whether a less complex - but still highly effective - lure can be developed to augment the efficacy of current vision-based stable fly traps.