Enhancement of Dacine Fruit Fly Management by Combining SIT with MAT and Female Suppression

The sterile insect technique (SIT) is most effective for pest insect population suppression when the ratio of sterile to wild males is large. This reduces the probability of wild females mating with wild males and compensates for the lower competitiveness of sterile males that has sometimes been reported. Due to the density-dependence of successful SIT, there are cases when its integration with other pest control tactics is beneficial. For example, the male annihilation technique (MAT) can be used to suppress males in wild populations of certain pest fruit flies in the subgenus Dacinae (including the genera Bactrocera, Dacus and Zeugodacus), which drastically increases sterile to wild male overflooding ratios and therefore SIT cost-effectiveness. The key to enabling the combination of SIT and MAT is to ensure that released sterile males are not responsive to MAT formulations so that they replace the wild males. Semiochemical treatments exist that improve the sexual performance of sterile male dacine fruit flies and reduce their response to MAT, but reliable, feasible, and cost-effective procedures to implement them at an operational scale still need to be developed and refined. MAT is also not an available tactic in some member states either due to accessibility to consumables or regulatory hurdles. An alternative is to suppress wild females to some extent. This would reduce damage by females laying eggs into fruit and vegetables, while also changing the ratio of sterile males to wild females. Despite the clear benefits that female attractants offer for pest suppression, their development is not at an advanced stage and requires further screening for potential candidates, and validation at the laboratory and field level. The combination of male replacement, plus sterile male enhanced performance and fewer female targets for them to mate with increases what can be achieved with the same number of sterile flies: treating a wider area or enabling more rapid suppression or eradication. Furthermore, due to the increased cost-effectiveness, decisions to invest in SIT may be facilitated in situations where this would not otherwise be feasible. The CRP objective is to fully develop the potentially synergistic relationship between MAT and SIT when applied simultaneously, and better suppress females in wild populations, to dramatically improve the efficacy of dacine fruit fly management. The assessment of semiochemicals to enhance dacine species SIT application against these pest fruit flies will include: - Develop practicable delivery systems for semiochemical treatment of the males of major dacine pest species and assess their effects and mode of action on sexual maturity, mating performance, and response to MAT traps or devices. - Identification and development of promising female attractants for dacine fruit flies that can be used to suppress wild populations using an attract-and-kill approach. - Evaluation of key parameters in large field cages such as wild fly sex ratio (simulating MAT or female suppression), degree of lure response by sterile flies, sterile:wild over-flooding ratio, bisexual release, and interference from natural sources of semiochemicals to determine their influence on the effectiveness of simultaneous MAT and SIT. - Field evaluation of simultaneous SIT with either MAT or female suppression, within a pilot setting that includes compatible management practices.