Phytosanitary Cold Treatment of the Spotted Wing Drosophila (Diptera: Drosophilidae) in Postharvest ‘Red Globe’ Grapes

Abstract

The spotted wing drosophila, Drosophila suzukii (Matsumura), is currently distributed in the main soft-skinned fruits production areas in China and 59 other countries, presenting a significant threat to importing nations. Optimal phytosanitary treatments, including fumigation, irradiation, and cold treatment, have been developed to prevent the international movement of this invasive fly. To determine the most cold-tolerant stage and facilitate the development of the technical schedules requested by the Technical Panel on Phytosanitary Treatment (TPPT), cold treatments of D. suzukii immature stages in ‘Red Globe’ grapes were conducted. Dose–mortality data at 0 °C and 2 °C from repeated trials were subjected to analysis of covariance, linear regression, and probit analysis. Results identified 3 d old pupae as the most cold-tolerant stage, followed by 1 d old pupae, 4 d old larvae, and 6 h old eggs with similar tolerance. The 2 d old larvae were the most sensitive stage. In subsequent confirmatory tests, 3 d old pupae were subjected to cold treatment at 0 °C for 9 and 10 days, and at 2 °C for 10 and 12 days, based on the probit estimation of the probit-9 value. No adult emergence occurred in the confirmatory tests except for one deformed adult from a 2 °C 10 d treatment. Therefore, the recommended treatment schedule requires fruit temperatures below 0.00 °C (or 1.62 °C) for no less than 10 (or 12) continuous days, with treatment efficacy not less than 99.9960% (or 99.9955%) at a 95% confidence level, respectively. These schedules are intended for submission to TPPT for the development of phytosanitary treatment standards.