Sulfur dioxide (SO2) fumigation was evaluated for postharvest control of navel orangeworm (NOW), Amyelois transitella, on stored pistachios in a laboratory study. Adsorption of SO2 by pistachios was measured at different temperatures for 24 h. As SO2 levels declined rapidly after SO2 injection, a short duration of 3 h was selected to evaluate effects of SO2 fumigation against NOW at different life stages. Effective controls of eggs, larvae, and pupae were achieved in 3 h fumigations. However, larvae in infested pistachios were most tolerant and eggs were most susceptible to SO2 fumigation. Complete controls of eggs, larvae, and pupae were achieved in 3 h fumigations with 0.2, 2.0, and 1.0% SO2. Large SO2 fumigation trials each with 4.5 kg pistachios were conducted and complete control of NOW larvae were achieved in 3 h fumigation with about 1.7% SO2 at ambient temperatures of 18-21°C. The results showed that SO2 fumigation has potential to control NOW on stored pistachios as well as to control other postharvest pests on stored products.
