Irradiation quarantine treatment for control of Sitophilus oryzae (Coleoptera: Curculionidae) in rice

Irradiation is a quarantine treatment option for stored products pests. Dose response tests were conducted to identify a post-harvest radiation treatment that would control rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in rice. Rice infested with adult or immature weevils was treated at radiation doses of 30, 60, 90, or 120 Gy, or left untreated as a control. Live and dead beetles were counted weekly for 15-24 weeks. Treatment of adult weevils at a radiation dose of 120 Gy resulted in no live adults after two weeks, indicating that this radiation dose caused adult mortality and sterility, whereas a total of 1261 adult beetles emerged during 24 weeks in the untreated controls. Treatment of immature life stages (a mixture of eggs, larvae and pupae) with a radiation dose of 90 or 120 Gy resulted in no adults emerging after five or two weeks, respectively, indicating that these doses prevented reproduction, whereas a total of 4275 adults emerged throughout 15 weeks in the untreated controls. Weight loss of rice infested with immature or adult weevils was significantly reduced by irradiation treatment at 60 Gy and 120 Gy. In a large-scale confirmatory test, a radiation dose of 120 Gy applied to 38,025 adult weevils in rice resulted in no reproduction. Irradiation at 120 Gy will provide quarantine security for rice weevil, and prevent post-irradiation weight loss caused by insect feeding in the commodity. Irradiation may be particularly helpful in controlling phosphine-resistant populations, and could help manage resistance by preventing the spread of resistant weevils in exported grains. Published by Elsevier Ltd.