Extended holding period and yeast hydrolysate in pre-release diet increase abundance of mature sterile Queensland fruit fly males in the field

Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), is a significant pest of horticultural crops in Australia. The sterile insect technique (SIT) is currently employed to eradicate outbreaks in fruit fly free regions and may also be used to suppress populations in endemic regions. For SIT to succeed, it is imperative that the released sterile males survive, disperse, attain sexual maturity, and are sexually competitive against their wild rivals. Q-fly SIT programmes have conventionally held adult flies for two to three days and have sometimes fed them only sugar before release, providing little time or nutrition for development prior to release. We investigated whether a 5-d pre-release holding period and provision of yeast hydrolysate (YH) together with sugar in the pre-release diet increase abundance of mature male Q-fly in the field. Indicating increased survivorship and/or maturation, the combination of YH feeding and 5-d pre-release holding period resulted in 6–8 times more recaptures of mature male flies in cuelure traps than was the case for flies released at 2 d with or without YH and for flies released at 5 d without YH. Flies held for 5 d and fed YH were relatively more abundant than flies from other treatments in traps close to the release point and were as abundant as other treatments in traps at the greatest assessed distances. These findings strongly support a recommendation that sterile Q-flies be provided a pre-release diet of YH and sugar and be held for 5-d post-eclosion before release.