Olfactory responses of tsetse flies to phenols from buffalo urine

A comparison was made of the EAG responses of males and females of Glossina morsitans morsitans Westwood, G. austeni Newstead and G. tachinoides Westwood to various doses of compounds known to be components of ox and buffalo urine fractions which are attractive to tsetse in the field (phenol, 3- and 4-methylphenol, 3- and 4-ethylphenol, 4-n-propylphenol, dimethylsulfone). All three species did not respond to dimethylsulfone. The overall responses to the phenolic substances were higher in females than in males in G.m.morsitans and higher in males than in females in G. austeni and G. tachinoides. Response spectra of the species for the phenolic substances suggested that G.m.morsitans and G. austeni were most responsive to 3- and 4-methylphenol and 3-ethylphenol, whereas G. tachinoides was most sensitive to 3-ethylphenol and 3-methylphenol, and only moderately sensitive to 4-methylphenol.Cross-adaptation experiments, in which 1-octen-3-ol, acetone, 4-heptanone and 3-nonanone were also included, revealed that all phenolic compounds stimulated one and the same class of receptors, which differed from the class of receptors activated by 1-octen-3-ol. The ketones also had their own receptors. Hence, the flies can obtain information about the presence of attractants by at least three different receptor classes. It was concluded that phenol and any individual alkylphenol found in ox and buffalo urine should be attractive to tsetse flies, provided that stimulus intensity is above threshold and not beyond optimum. One class of receptors may respond more strongly in males than in females, whereas another class is more responsive in females than in males. This may result in a change in sex ratios in catches depending on the odour bait used.