Perception of conspecific female pheromone stimulates female calling in an arctiid moth, Utetheisa ornatrix

Perception of the female sex pheromone in Utetheisa ornatrix (Lepidoptera: Arctiidae) is responsible for induction and adjustment of calling by females and the collective phenomenon termed "female pheromonal chorusing". We found five olfactory-active compounds in the U. ornatrix female gland. When females were exposed to the entire pheromone or to two of its (synthetically prepared) components, (Z,Z,Z)-3,6,9-eicosatriene and (Z,Z,Z)-3,6,9- heneicosatriene, they were more likely to call during a given night, begin calling earlier, and briefly increase signal frequency with which they extrude their abdomen, an observable indication of calling in this species. Some females even initiated calling during photophase when exposed to the pheromone components. In general, female U. ornatrix are more sensitive to the complete blend of pheromone than to its individual compounds. We also tested the hypotheses: 1) that abdominal extrusion per se increases the rate of pheromone release; and 2) that greater abdominal pumping rhythm increases pheromone release rate. Contrary to our expectations: 1) females did not respond more strongly to a pulsed pheromone stimulus than to the constant release of pheromone at the same average release rate; and 2) we did not find a relationship between the frequency of abdominal pumping and pheromone release rate. Possible explanations for these unexpected findings are discussed.