Synergistic Effect of Cold Treatment Combined with Ethyl Formate Fumigation against Drosophila suzukii (Diptera: Drosophilidae)

SIMPLE SUMMARY: A synergistic effect on Drosophila suzukii control was observed by combining EF fumigation with cold-temperature treatment. D. suzukii showed higher mortality at 1 °C after exposure to cold temperature. The egg stage showed the highest tolerance in the ethyl formate fumigation-only treatment according to the LCT(99) value in a 12 L desiccator. Among the combination treatment methods, cold treatment after EF fumigation was found to be the most effective for D. suzukii control, and mortality increased as the duration of exposure to cold temperature increased. Although the sorption of EF was very high, the concentration of fumigant during treatment had a significant effect on insecticidal activity during combination treatment. Therefore, the combination of EF fumigation and cold-temperature treatment can be used to control D. suzukii. ABSTRACT: Drosophila suzukii is a quarantine pest that is rapidly spreading in berries. This study evaluated the synergistic effect of combination treatment with ethyl formate (EF) and cold temperature for D. suzukii control on imported grapes. A higher insecticidal effect was observed at 1 °C than at 5 °C at all developmental stages, and the pupal stage showed the strongest tolerance to cold temperature. After EF fumigation alone, eggs showed the highest tolerance at 216.67 mg·h/L (LCT(99) value), and adults showed the highest susceptibility at <27.24 mg·h/L. Among the combination treatment methods, cold temperature after fumigation resulted in the best synergistic effect. The effect of this combination was significant, with 23.3% higher mortality for eggs, 22.4% for larvae, and 23.4% for pupae than observed with EF fumigation alone. Furthermore, the period of complete D. suzukii control in the 12 L desiccator was shorter in the combination treatment group at the LCT(80) value than at the LCT(50) value of the egg stage. EF showed a very high sorption rate (24%) after 4 h of exposure at a grape loading ratio of 15% in a 0.65 m(3) fumigation chamber. As the grape loading ratio for combination treatment decreased, D. suzukii mortality increased, but when EF was administered at the LCT(80) value, there was little difference in the mortalities of the eggs and larvae but not the pupae. All D. suzukii developmental stages were completely controlled within 7 days after combination treatment, and phytotoxicity was not observed in grapes. These results suggest that the combination of cold-temperature treatment and EF fumigation could be used for D. suzukii control.