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 (CO₂), methane (CH₄)] 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) CO₂ and CH₄ interactively attract stable flies, (2) CO₂ 'gates' attraction of stable flies to CH₄, and (3) breath volatiles on their own, or in combination with both CO₂ and CH₄, attract stable flies. In Y-tube olfactometer experiments, the blend of CH₄ (0.5%) and CO₂ (1%) in breathing air ('b-air') attracted significantly more female flies than CH₄, or CO₂, in b-air. The flies' responses to CH₄ were contingent upon their prior or concurrent exposure to CO₂. In two-choice experiments in a large greenhouse compartment, significantly more flies landed on the host-look-alike barrel that disseminated a blend of CO₂ and CH₄ in b-air (CO₂/CH₄/b-air) than on the barrel disseminating either b-air or CO₂. Moreover, significantly more flies landed on the barrel that disseminated synthetic breath volatiles (SBVs) than on the barrel disseminating b-air. The blend of CO₂/CH₄/b-air and SBVs elicited more fly landings on barrels than CO₂/CH₄/b-air but not than SBVs. SBVs, possibly combined with both CH₄ and CO₂, could be developed as a lure to enhance trap captures of stable flies in livestock production facilities.