SEARCH FOR TSETSE ATTRACTANTS - A STRUCTURE-ACTIVITY STUDY ON 1-OCTEN-3-OL IN GLOSSINA FUSCIPES FUSCIPES (DIPTERA, GLOSSINIDAE)

Trapping tsetse flies belonging to the palpalis group still relies tot ally upon luring by visual cues even though odor-baited trapping is us ed effectively against the morsitans-group species. Forty-three percen t of the antennal olfactory cells of Glossina f. fuscipes, a member of the palpalis group, respond to 1-octen-3-ol. For this species we repo rt a structure-activity relationship between 1-octen-3-ol analogs, in which carbon chain length and the configuration of the hydroxyl and pi -bond moieties are varied, and biological activity. Although the optim um chain length for all cells sensitive to 1-octen-3-ol is eight and m ost cells give lower responses when the hydroxyl function is omitted, there is a clear division into two groups. One group is diverse and re presents cells that appear indifferent to the presence or position of the pi bond; many will respond to such disparate structures as acetone and 3-methylphenol as well as to 1-octen-3-ol. In the other group, th e structural requirements for the stimulus are more stringent; the cel ls appear to be specifically tuned to 1-octen-3-ol. Their thresholds a re three orders of magnitude lower than those of the former group. The existence of two clusters points to a functional division in the olfa ctory sense. We suggest that the latter low-threshold group is involve d in host detection from a distance while the former diverse group is involved in host discrimination at close range. Trap harvests with 1-o cten-3-ol as a bait may have been disappointing because the appropriat e mixture for generating a landing response on the traps is still lack ing.