Improved pre-release management to enhance the efficacy of the Queensland fruit fly Bactrocera tryoni (Froggatt) sterile insect technique

Queensland fruit fly, Bactrocera tryoni  (Froggatt) (Diptera: Tephritidae ) 'Q-fly' presents a  serious pest management challenge and biosecurity risk in Australia. Q-fly infests more than 300 species of cultivated fruits and vegetables, including many major commercial crops, and causes significant restrictions to market access.  The sterile insect technique (SIT) has been used to manage Q-fly in some regions and is increasingly favored as a sustainable practice. In SIT millions of sterile flies are released to suppress reproduction of pest populations. Released sterile males mate with wild females, resulting in unfertilized eggs and a generational decline in pest abundance. However, high field mortality of the sterile flies can constrain success of Q-fly SIT. Further, the adult maturation phase is lengthy, and this can present logistical and performance challenges for SIT. Pre-release nutrition, hormones, and semiochemicals have been investigated as means to increase survival and to accelerate maturation after release. However, there remains a need to validate effectiveness of different pre-release treatments, such as yeast hydrolysate (YH), raspberry ketone (RK) and methoprene in the field. Further, there remains a need for improved understanding of how released flies respond to habitat and abiotic conditions in the field. My thesis addresses this need. Initial studies involved investigation of how RK supplements affect responses of Q-fly antennae and maxillary palps to cuelure, finding no effects and suggesting up-stream processes as mediator of suppressed behavioural responses. I t hen investigated the effectiveness of pre-release treatments of YH with and without RK or methoprene, and the effects of extended pre-release holding, on field performance. RK and methoprene treatments greatly increased recapture rates when flies were released at two days of age but not at five days of age, with this difference explained mostly by greatly increased recapture rates following releases at five days that apparently left little room for further increase. Strong positive effects of pre-release YH feeding were confirmed. Weather conditions, particularly temperature, and host plants affected recapture rates and field distribution. Overall, my thesis provides key advances that will substantially improve the efficacy and cost-effectiveness of Q-fly SIT, increasing the viability of SIT as a mainstream practice for management of outbreaks and established populations.