Quarantine Disinfestation of Papaya Mealybug, Paracoccus marginatus (Hemiptera: Pseudococcidae) Using Gamma and X-rays Irradiation

SIMPLE SUMMARY: The papaya mealybug is a highly polyphagous invasive pest that poses a quarantine threat to tropical and subtropical countries. Infested commodities in international trade should be subject to phytosanitary treatment, and irradiation treatment is recommended to replace methyl bromide fumigation. The irradiation treatments were conducted on the gravid females and 2-, 4-, and 6-day-old eggs of Paracoccus marginatus to develop a technical schedule for phytosanitary purpose. The results showed no significant difference among gravid females and 2-, 4-, and 6-day-old eggs after exposure to a range of X-ray radiation (15–105 Gy). Moreover, the minimum radiation dose for providing quarantine security was estimated and validated in the preliminary and confirmatory tests. In the gamma radiation confirmatory tests, no nymphs emerged when a total of 60,386 gravid females were exposed to a radiation dose range of 146.8 to 185.0 Gy. Following the standard-setting principles, the largest dose value in confirmatory tests is the minimum threshold for phytosanitary treatment. As a result, we strongly recommend a minimum dose of 185 Gy for the phytosanitary irradiation of papaya mealybug-infested commodities, and the treatment efficacy is not less than 99.9950% at the 95% confidence level. ABSTRACT: Paracoccus marginatus is a highly polyphagous invasive pest that poses a significant quarantine threat to tropical and subtropical countries. Infested commodities in international trade should undergo phytosanitary treatment, and irradiation is recommended as a viable alternative to replace methyl bromide fumigation. Dose-response tests were conducted on the 2-, 4-, and 6-day-old eggs and gravid females of P. marginatus using the X-ray radiation doses of 15–105 Gy with an interval of 15 Gy. Radiotolerance was compared using ANOVA, fiducial overlapping and lethal dose ratio (LDR) test, resulting in no significant difference among treatments, except for the overall mortality and LDR at LD(90) (a dose causing 90% mortality at 95% confidence level). The estimated dose for LD(99.9968) was 176.5–185.2 Gy, which was validated in the confirmatory tests. No nymphs emerged from a total of 60,386 gravid females exposed to a gamma radiation dose range of 146.8–185.0 Gy in the confirmatory tests. The largest dose in confirmatory tests should be the minimum threshold for phytosanitary treatment, consequently, a minimum dose of 185 Gy is recommended for the phytosanitary irradiation treatment of papaya mealybug-infested commodities, ensuring a treatment efficacy of ≥99.9950% at 95% confidence level.