Activity patterns of Queensland fruit flies (Bactrocera tryoni) are affected by both mass-rearing and sterilization

Mass-reared sterile tephritid flies released in sterile insect technique (SIT) programmes exhibit behaviour, physiology and longevity that often differ from their wild counterparts. In the present study, video recordings of flies in laboratory cages are used to determine whether the sequential processes of mass-rearing and sterilization (using gamma radiation) that are integral to SIT affect general activity patterns of male and female Queensland fruit flies Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) ('Q-flies'). Compared with wild flies, mass-reared flies exhibit a marked reduction in overall activity, and further reduction is found after sterilization. In terms of the frequency of activities, both fertile and sterile mass-reared Q-flies fly less often and exhibit more bouts of inactivity and grooming than wild Q-flies. In addition, in terms of the duration of activities, fertile and sterile mass-reared Q-flies spend less time flying and more time walking, grooming and being inactive than wild Q-flies. Although fertile and sterile mass-reared flies are similar in other regards, sterile mass-reared flies spend more time being inactive than fertile mass-reared flies. These findings raise new questions about how changes in behaviour and activity levels may influence the performance of mass-reared sterile Q-flies in the field, as well as the physiological and metabolic processes that are involved. The frequency and duration of inactivity could provide a simple but powerful and biologically relevant test for quality in mass-rearing and SIT programs.