Combined Effects of Cold Treatment and Phosphine in Drosophila suzukii (Diptera: Drosophilidae)

This study analyzed the effect of combined phosphine (PH3) fumigation and low-temperature treatment on the control of Drosophila suzukii. In the low-temperature, single-treatment experiment, there was no significant difference in insecticidal activity between 1 °C and 5 °C except in D. suzukii adults. Adults showed 98.0% mortality after exposure to 1 °C for 7 d. Regarding fumigation treatment with PH3 alone, adults were the most susceptible, and pupae had the highest tolerance. Combined low-temperature treatment and fumigation showed a synergistic effect, except in the egg stage, and showed slight synergistic effects in larvae and pupae regardless of the combined treatment order. In pupae, the combination group exposed to 1 °C for 24 h after exposure to PH3 for 4 h had the lowest LCT99 value, at 10.49 mg·h/L. The sorption rate of PH3 on grapes decreased to 85.49% after 4 h of exposure, with a 15% loading ratio (w/v), and there was no significant difference in various criteria of phytotoxicity in exposed grapes compared to control, even after 14 d of combined treatment. Therefore, this study indicates that combined PH3 fumigation and low-temperature treatment could be useful in D. suzukii control.