The role of sex pheromones in initiation of copulatory behaviour by male tsetse flies, <i>Glossina morsitans morsitans</i>

Abstract

ABSTRACT. Copulatory responses to a variety of decoy objects baited with synthetic 15,19,23‐trimethylheptatriacontane were induced in adult male Glossina morsitans morsitans Westw., provided the object was of similar shape and size to a female fly. Chemical and configurational (shape and texture) stimuli were important in eliciting and maintaining copulatory behaviour of males. A dose/response relationship was obtained from 7‐day‐old test males, with an ED 95 of 2 μg using as decoys solvent‐washed dead males baited with 15,19,23‐trimethylheptatriacontane. The quantity of this compound in 5‐day‐old adult females is more than 4.0 μg; in males, only 0.6 μg. It is considered to have the characteristics of a true contact sex pheromone for the species, and does not act synergistically with other less stimulatory synthetic compounds. Gas chromatographic analysis of adult female cuticular paraffins of G.m.morsitans showed the presence of two large peaks between C 37 and C 38 which were virtually absent in males. Young adults of both sexes possessed a series of hydrocarbons below C 29 which disappeared during the first few days of adult life. The natural pheromone appears on the pharate adult female about 2 days before emergence from the puparium and is present throughout life. This suggests it is a component of the surface cuticular waxes. Responsiveness of males to pheromone‐baited decoys increased to a maximum 3–4 days after emergence in regularly fed flies and only declined during the 24 h prior to death from starvation.