Associations between diurnally varying male volatile emissions and allochrony in 2 sibling fruit fly species (Diptera: Tephritidae)

Allochrony can be an important premating isolating mechanism in insects but its physiological basis has seldom been determined. It operates at a diurnal scale to differentiate mating times of some closely related tephritid taxa. For example, the sympatric sibling species Bactrocera tryoni (Froggatt) and Bactrocera neohumeralis (Hardy) mate at dusk and during the day, respectively. Rectal gland emissions of courting males function as sex pheromones in B. tryoni and recent evidence shows differences between the 2 species in many volatiles released from crushed rectal glands. Here we use gas chromatography–mass spectrometry to show that the head space compositions of whole male emissions of each species are generally but not invariably correlated with those of their respective rectal glands and they also differ between the species. Further, while the compositions of the whole male emissions do not vary diurnally in either species, the total amounts of the emissions do, in species-specific ways, with those of B. tryoni higher at dusk and night and those of B. neohumeralis higher during the day. Thus, the species differ substantially in their diurnal patterns of total whole fly emissions in a manner consistent with their allochrony, while the compositions of the emissions also differ substantially, which could also contribute to their premating isolation but is independent of their allochrony.