Raspberry ketone as a promising pre-release supplement for the Sterile Insect Technique (SIT) of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

Queensland fruit fly, Bactrocera tryoni Froggatt (Qfly) (Tephritidae), Australia’s most economically damaging fruit fly, infests more than 100 hosts including many commercially important crops. Control of this pest is based on insecticides, bait sprays, male annihilation technique (MAT), and in some regions sterile insect technique (SIT). SIT can be a highly effective control method, and is used around the world to control some of the worst fruit fly pests, but high field mortality of the sterile flies can constrain the success of Qfly SIT. Improved quality of released males and acceleration of sexual maturation can help to overcome this problem. In this thesis I investigated potential beneficial effects of supplementing immature Qflies with raspberry ketone (RK), a metabolic enhancer. RK was mixed with the diet for 48 hours, a duration consistent with standard pre-release holding periods.When RK was provided together with yeast hydrolysate (YH), RK-fed males exhibited accelerated development of reproductive organs and increased mating propensity when 6 - 9 days of age. Positive effects of RK were not evident in males that were fed only sugar, and no positive effects of RK were evident for female development regardless of diet. As sex pheromone plays important role in calling and courtship, I investigated effects of RK on pheromone production. RK-fed males produced significantly more pheromone, and RK was detected in the pheromone blend. Increased pheromone production and presence of RK in pheromone blend may be an important factor in elevated mating propensity of RK-fed male Qflies. While mating is an important step in SIT, female remating behaviour is also important as females that mate with a released male and then a wild male will likely retain fertility. Females that mated with RK-fed males, including during the period of accelerated development, exhibited remating tendency that was similar to females mated by control males. That is, not only does RK feeding increase development rate and early mating propensity of male Qflies, the early matings of RK-fed males are of undiminished effectiveness. SIT could potentially be greatly enhanced if combined with MAT, and my studies have identified a potential new way to enable this. In some other Bactrocera, mature males that feed on lures are then unresponsive to lures for substantial periods, and so would not be attracted to MAT devices. However, combination of SIT and MAT has been considered unsuitable for Qfly owing to long adult maturation period and high mortality in attempts to hold the flies to maturity before release. I found that RK-fed males exhibit a persistent reduction in responsiveness to cuelure traps, opening the possibility of simultaneous MAT and SIT application in Qfly control programmes. In addition to considering potential beneficial effects of pre-release RK supplements it is also important to consider potential drawbacks for survival. When a source of protein + sugar was available throughout life, RK supplements did not affect survival. However, RK supplements did increase susceptibility to desiccation and food deprivation in the period immediately following pre-release treatment. This thesis comprises the first series of studies to consider RK as a potential pre-release treatment for SIT in the context of a standard 2 - 3 day pre-release holding period. The substantial beneficial effects of RK supplements on development, mating, and lure response support a strong case for further investigation and consideration for trial deployment on operational SIT programs.