Previous comparison of the body odors of tsetse-refractory waterbuck and those of tsetse-attractive ox and buffalo showed that a blend of 15 EAG-active compounds specific to waterbuck, including C5-C10 straight chain carboxylic acid homologues, methyl ketones (C8-C12 straight chain homologues and geranyl acetone), phenols (guaiacol and carvacrol) and δ-octalactone, was repellent to tsetse. A blend of four components selected from each class of compounds (δ-octalactone, pentanoic acid, guaiacol, and geranylacetone) showed repellence that is comparable to that of the 15 components blend and can provide substantial protection to cattle (more than 80%) from tsetse bites and trypanosome infections. Structure-activity studies with the lactone and phenol analogues showed that δ-nonalactone and 4-methylguaiacol are significantly more repellent than δ-octalactone and guaiacol, respectively. In the present study, we compared the responses of Glossina pallidipes and Glossina morsitans to i) blends comprising of various combinations of the most active analogues from each class of compounds, and ii) a four-component blend of δ-nonalactone, heptanoic acid, 4-methylguaiacol and geranyl acetone in different ratios in a two-choice wind-tunnel, followed by a field study with G. pallidipes population in a completely randomized Latin Square Design set ups. In the wind tunnel experiments, the blend of the four compounds in 6:4:2:1 ratio was found to be significantly more repellent (94.53%) than that in 1:1:1:1 proportion and those in other ratios. G. m. morsitans also showed a similar pattern of results. In field experiments with G. pallidipes population, the 6:4:2:1 blend of the four compounds also gave similar results. The results lay down useful groundwork in the large-scale development of more effective 'push' and 'push-pull' control tactics of the tsetse flies.
Keywords: Blending studies; Savanna tsetse; Tsetse-repellency; ‘push’-tactic.
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