Modified atmosphere under cold storage does not reduce phytosanitary irradiation efficacy for Drosophila suzukii (Diptera: Drosophilidae)

Phytosanitary irradiation (PI) has been advancing consistently in recent years, partly due to its broad applicability to fresh produce and insect pests. Internationally adopted PI treatment schedules cover all plant hosts associated with a target pest. Thus, it is crucial to evaluate the impact of commodity-related postharvest practices on PI efficacy. For instance, modified atmospheres (MA) used to extend the shelf life of fresh produce might increase insect radiotolerance. Hence, we tested the extent to which combining atmospheric (severe hypoxia-N2, severe hypoxia-CO2, hypoxia, and normoxia) and storage conditions (25 and 0 °C) affects PI efficacy against Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). Late pupae of D. suzukii were irradiated at nominal doses of 52 Gy (suboptimal dose) and 72 Gy (PI dose). Prevention of egg laying was considered the treatment endpoint. Our results showed that egg laying was prevented in PI-treated females at 72 Gy, regardless of atmospheric or storage conditions. Females irradiated with the suboptimal dose of 52 Gy under severe hypoxia laid significantly more eggs than in normoxia or hypoxia. Ovary dissections and scanning electron microscope (SEM) imaging confirmed irreversible damage in the reproductive tract of PI-treated D. suzukii females. We conclude that a minimum absorbed dose of 80 Gy is effective for D. suzukii, preventing egg laying even under modified atmosphere and cold storage conditions.