Disinfestation of Wheat Infested with Sitophilus oryzae Using Ozone Gas

ABSTRACT The use of non-conventional methods in the management of stored product insect pests is gaining popularity, particularly due to problems associated with chemical control. The effect of ozone on Sitophilus oryzae (L.) (Coleoptera: Curculionidae), an internal feeder of stored wheat and other grains, was investigated using dose-response experiments. Eggs, immature stages within wheat kernels, and adults were exposed to an ozone concentration of 200 ppm for 6, 18, and 30 h. Insect life stages were placed at a depth of 5, 15, and 25 cm in wheat filled in PVC pipes. Effect of ozone on S. oryzae life stages was evaluated as the percent mortality of treated eggs, immature stages, and adults. Egg mortality was recorded as the percentage of eggs that failed to hatch 10 d after treatment (DAT), and mortality in immature stages was recorded as the percentage of immature insects that failed to develop into adults 28 DAT at 28°C. Mortality of adults was recorded as the percentage that died 0, 1, and 2 DAT. Egg mortality at the 5 cm depth in wheat exposed to ozone for 30 h was significantly higher than the mortality when exposed for 18 h. When the three depths were compared, at 18 h and 30 h exposure times, fewer adults emerged from immature insects placed at 5 cm compared with insects placed at 15 or 25 cm depths. Adult mortality in insects placed at the 5 cm depth for all exposure times was significantly higher than at 15 and 25 cm at 2 DAT. Findings from this study suggest that ozone may be an effective fumigant; however, mortality of S. oryzae life stages is dependent on the exposure time, depth of occurrence in the wheat mass, or post treatment time (DAT).