Olfactory and behavioural responses of tsetse flies, <i>Glossina</i> spp., to rumen metabolites

Herbivores provide tsetse flies with a blood meal, and both wild and domesticated ruminants dominate as hosts. As volatile metabolites from the rumen are regularly eructed with rumen gas, these products could serve tsetse flies during host searching. To test this, we first established that the odour of rumen fluid is attractive to hungry <i>Glossina pallidipes</i> in a wind tunnel. We then made antennogram recordings from three tsetse species (<i>G. pallidipes</i> morsitans group, <i>G. fuscipes</i> palpalis group and <i>G. brevipalpis</i> fusca group) coupled to gas chromatographic analysis of rumen fluid odour and of its acidic, mildly acidic and neutral fractions. This shows tsetse flies can detect terpenes, ketones, carboxylic acids, aliphatic aldehydes, sulphides, phenols and indoles from this biological substrate. A mixture of carboxylic acids at a ratio similar to that present in rumen fluid induced behavioural responses from <i>G. pallidipes</i> in the wind tunnel that were moderately better than the solvent control. The similarities in the sensory responses of the tsetse fly species to metabolites from ruminants demonstrated in this study testify to a contribution of habitat exploitation by these vertebrates in the Africa-wide distribution of tsetse.