Effect of the sterile insect technique (SIT) on predator-prey interactions in Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae)

Queensland fruit fly (Q-fly) is a serious horticultural pest known to infest over hundreds of economically important fruits and vegetables in Australia. Sterile insect technique (SIT) is currently a wide-spread method to control its wild population. Domestication and irradiation of laboratory reared flies are the two key steps in SIT, however, these processes are likely to affect the performance of SIT released flies negatively. High-density mass rearing is expected to reduce the flies’ awareness of their surroundings and irradiation lowers activity, emergence, flight ability and survival. Previous work suggests that Q-flies (including SIT released flies) are targeted by many predators in the field. These circumstances are concerning as SIT released flies are predicted to be predated more than wild counterparts. However, to date no detailed study has been conducted to test the influence of natural predators on Q-fly survival and reproduction, including SIT released flies. Therefore, my thesis investigated the effect of natural predators on Q-fly survival and reproduction. My study offers an evaluation for current SIT control, emphasising the effect of domestication and irradiation on released fly behaviour against their natural predators. My thesis research confirmed that the together with SIT, natural predators play a significant role in controlling wild Q-fly populations through direct (predation) and indirect (lowering reproduction) effects. Interestingly, the domestication and irradiation process did not detrimentally affect the SIT released fly behaviour against their natural predators. However, my results confirmed that domestication affects behaviour, including mating behaviour, which may need to be further considered to improve the success of the SIT process. Overall, the results in this thesis suggest that the SIT process does not affect the predator-prey interaction in Q-flies, and released sterile males are not at a disadvantage when they are exposed to predators compared to wild counterparts. However, SIT released flies may differ in other aspects such as reproductive behaviour, which may have direct consequences on the effectiveness and efficiency of current Q-fly control measures. Therefore, further studies are recommended to identify the underlying mechanisms of these results, thereby improving SIT control of this pest.