a1 Department of Primary Industries, Entomology Branch, Meiers Road, Indooroopilly, Queensland 4068, Australia
Adults of Dacus spp. feed on plant surface bacteria. The responses of D. tryoni (Froggatt) and D. cacuminatus (Hering) to some components of bacterial odours and to cue-lure were tested in a field-cage olfactometer, in studies in south-eastern Queensland. One component of bacterial emission, 2-butanone, attracted D. tryoni (a species responding to cue-lure) but not D. cacuminatus (a species responding to methyl eugenol) and is suggested as the attractive portion of the cue-lure molecule. Sexually mature males and immature females of D. tryoni responded to 2-butanone, cue-lure and bacterial odours in field-cage tests. Females fed on sugar and water required protein hydrolysate to produce eggs, but males were fertile with or without protein. These different nutrient requirements, and the fact that males and females possess different crop colour and bacterial contents when feeding in the same host-plant, indicate that the sexes feed on different substrates. Consequently, the strong bacterial attractant cues in the host-tree may be a feeding attractant to females and a sex attractant to males. It is proposed that 2-butanone is an important rendezvous stimulant in nature, bringing the mature male flies into the feeding and oviposition sites (host-trees) of the developing females for mating encounters.
(Received June 17 1986)