The behaviour of the Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae), and its implications for improving integrated pest management using the sterile insect technique

Queensland fruit flies, Bactrocera tryoni Froggatt (Diptera: Tephritidae), are one of the most important pests of Australian horticulture due to the severity with which they limit domestic and international trade of host produce. The sterile insect technique (SIT) is used to extirpate or prevent the establishment of wild populations of B. tryoni in some regions, whereby millions of flies are reared, sterilised, and released into agricultural areas. Sterile males are expected to mate with wild females, resulting in infertility of wild females and a generational decline in the wild population. However, sterile B. tryoni often display poor quality arising from adaption to laboratory conditions and exposure to irradiation. These deficiencies can be identified and ameliorated through behavioural studies, which this thesis considered. In the studies described herein, I compared the behaviours of mass-reared (fertile and/or sterile) and wild B. tryoni. Furthermore, I investigated behaviours that likely take place in natural habitats. I investigated the microhabitat distribution of B. tryoni males and females from mass-reared (fertile and sterile) and wild populations in tree canopies through the day. Flies moved systematically through the tree canopy in response to shifting abiotic conditions (temperature, light intensity, and humidity). Next, I observed the spatial and temporal distribution of male mating behaviours (wild, and fertile and sterile mass-reared) at dusk in tree canopies. Mass-reared (both fertile and sterile) males exhibited mating behaviours that differed spatially and temporally from wild conspecifics, which likely attributed to a high tendency for assortative mating. In a laboratory study of the effect of sterilisation on the ability of B. tryoni to tolerate desiccation stress, sterilisation lowered its activity and survival under desiccation stress. Finally, in a study of male-male aggression, I documented the aggressive behaviours of B. tryoni males for the first time. Crowding reduced aggression and mass-reared adults engaged in aggression at a relatively close distance, both of which may negatively affect their ability to compete for resources or repel predators in nature. Through the studies described in this thesis, I highlight areas of improvement for the management of B. tryoni using SIT.