| Summary: | This study analyzed the effect of combined phosphine (PH<sub>3</sub>) fumigation and low-temperature treatment on the control of <i>Drosophila suzukii</i>. In the low-temperature, single-treatment experiment, there was no significant difference in insecticidal activity between 1 °C and 5 °C except in <i>D</i>. <i>suzukii</i> adults. Adults showed 98.0% mortality after exposure to 1 °C for 7 d. Regarding fumigation treatment with PH<sub>3</sub> 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 PH<sub>3</sub> for 4 h had the lowest LCT<sub>99</sub> value, at 10.49 mg·h/L. The sorption rate of PH<sub>3</sub> on grapes decreased to 85.49% after 4 h of exposure, with a 15% loading ratio (<i>w</i>/<i>v</i>), 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 PH<sub>3</sub> fumigation and low-temperature treatment could be useful in <i>D</i>. <i>suzukii</i> control.
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