Electron beam irradiation for management of in-shell pecan weevil larvae (Coleoptera: Curculionidae)

The pecan weevil, Curculio caryae (Horn) (Coleoptera: Curculionidae), is a direct pest of pecan nuts often causing economic injury. Larvae feed and develop within the pecan nut, mature fourth instars emerge from nuts during autumn, drop to the orchard floor and complete development underground. However, a proportion of pecan weevil larvae remain in nuts at harvest. We tested electron beam irradiation of pecan weevil larvae as a potential phytosanitary treatment against infested nuts being shipped to production regions free of pecan weevil. Irradiation doses of 0, 150, 400, 750, and 1,000 Gy were assayed against pecan weevil using different larval exposure methods (bare larvae [bare], larvae in microfuge tubes [tube], and larvae in microfuge tubes placed into empty pecan shells [nut]). After treatment application, larvae were held singly in Petri dishes at 15 °C and examined for 60 d to determine mortality. Results revealed that larval mortality increased with days after treatment for each irradiation dose, including 0 Gy, for the 3 exposure methods. Mortality was generally lower for larvae in the tube and nut at 400, 750, and 1,000 Gy than for bare larvae. Overall mortality was lower for lower irradiation doses but higher for higher doses, and over time no larvae survived 1,000 Gy. These results strongly suggest that irradiation is an effective method to control in-shell pecan weevil larvae.