Carbon Dioxide, Methane, and Synthetic Cattle Breath Volatiles Attract Host-Seeking Stable Flies, Stomoxys calcitrans.

Stable flies, Stomoxys calcitrans (L.), are blood-feeding ectoparasites of cattle. Host-seeking stable flies respond to various cattle host cues, but a potential role of cattle breath gases [carbon dioxide (CO), methane (CH)] and cattle breath volatiles (acetone, isoprene, 2-butanone, 2-propanol, propionic acid, 3-methyl butyric acid, phenol), alone or in combination, on host-seeking behavior of stable flies has not yet been comprehensively investigated. In laboratory and greenhouse experiments, we tested the hypotheses that (1) CO and CH interactively attract stable flies, (2) CO 'gates' attraction of stable flies to CH, and (3) breath volatiles on their own, or in combination with both CO and CH, attract stable flies. In Y-tube olfactometer experiments, the blend of CH (0.5%) and CO (1%) in breathing air ('b-air') attracted significantly more female flies than CH, or CO, in b-air. The flies' responses to CH were contingent upon their prior or concurrent exposure to CO. In two-choice experiments in a large greenhouse compartment, significantly more flies landed on the host-look-alike barrel that disseminated a blend of CO and CH in b-air (CO/CH/b-air) than on the barrel disseminating either b-air or CO. Moreover, significantly more flies landed on the barrel that disseminated synthetic breath volatiles (SBVs) than on the barrel disseminating b-air. The blend of CO/CH/b-air and SBVs elicited more fly landings on barrels than CO/CH/b-air but not than SBVs. SBVs, possibly combined with both CH and CO, could be developed as a lure to enhance trap captures of stable flies in livestock production facilities.