Plant volatile-based fumigation improves mating competitiveness of males for population suppression of the global fruit pest Cydia pomonella

The implementation of sterile insect technique (SIT) has proven effective in the area-wide suppression of several significant agricultural and sanitary pests by employing traditional cobalt-60 (60 Co-γ) as a radiation source. Recently, X-ray has been validated as a feasible alternative to 60 Co-γ radiation sources. Nonetheless, higher doses of X-ray irradiation lead to insect sterility but diminish mating competitiveness, thereby impacting the effectiveness of SIT applications. Thus, it is crucial to ascertain the optimal irradiation dose and develop strategies to enhance the mating competitiveness of sterile insects to enhance SIT efficacy. In this study, we determined the effect of various X-ray irradiation doses (ranging from 0 to 366 Gy) on the fecundity, fertility, and mating competitiveness of Cydia pomonella, a globally invasive fruit pest. Results demonstrated that the sterility rate of sterile males increased proportionally with irradiation dose up to 200 Gy, beyond which it plateaued. Notably, exposure to 200 Gy of irradiation notably decreased the mating competitiveness of male, as evidenced by a mating competitiveness index of 0.17 in laboratory and 0.096 in the orchard. This decline in mating competitiveness is likely linked to the down-regulation of genes associated with the recognition of sex pheromones, specifically CpomOR3a, CpomOR3b, and CpomOR5, following X-ray irradiation. Fumigation of the plant volatile, linalool at varying concentrations (70, 83, and 96 μL/m3) resulted in differential enhancements in male mating competitiveness, with the moderate concentration significantly improving the competitiveness of sterilized males, possibly by restoring their ability to recognize sex pheromones. Implementation of repeated releases of sterilized males on a pilot scale led to a notable reduction in the population of C. pomonella in the field. These findings indicate that fumigation with plant volatiles has the potential to mitigate male sterility induced by X-ray irradiation, offering a promising approach to enhance the efficacy of SIT applications for the control of C. pomonella.