Electrophysiological and behavioral responses of a Cuban population of the sweet potato weevil to its sex pheromone.
The sex pheromone of feral sweet potato weevils Cylas formicarius elegantulus from Cuba was found, via solid-phase microextraction analysis, to be identical to (Z)-3-dodecenyl (E)-2-butenoate, a previously reported compound. Females emitted 20 pg pheromone d-1. In scanning electron microscopy studies carried out on the male antenna, we identified several types of sensilla: sensilla trichoidea of type 1 (ST1) as long hairs (100-150 µm), sensilla trichoidea of type 2 as short hairs (50-60 µm), sensilla basiconica of type 1 as thick pegs (20-25 µm), sensilla basiconica of type 2 as curved pegs (10-15 µm), and sensilla basiconica of type 3 as thin and straight short pegs (15-20 µm). The same types were observed in female antennae but ST1 were far less abundant than in males. Sensilla chaetica were also found on the flagellum subsegments in both sexes. In electrophysiological tests, the crotonate function in the pheromone structure proved to be critical for activity since regular depolarizations (0.6-0.8 mV) were obtained with puffs on 1 µg of the attractant, but not with puffs of the formate, acetate, propionate, or butyrate analogue of the pheromone. In a double dual-choice olfactometer, males showed maximum activity between the 4th and the 8th hr of scotophase at a dose of 50-1000 ng of pheromone. In field tests, a correlation between the contents of the Z,E isomer in the pheromone formulation with activity was noticed, and baits containing this isomer of stereomeric purity >94% showed the highest attractivity. The presence of 5% of the Z,Z isomer in the lure did not induce any synergistic or inhibitory effect, and the alcohol precursor of the pheromone was inactive. The results show that use of a stereomerically pure pheromone may not be necessary in pest control strategies.