Comparison of susceptibility of two stored-product insects, Ephestia kuehniella Zeller and Tribolium confusum du Val to gaseous ozone

In this study, the susceptibility of two stored-product insects, Ephestia kuehniella and Tribolium confusum, to gaseous ozone was investigated. Two ozone fumigation methods were used, an empty space fumigation with only one flush of ozone treatment held for 2 h, and a reflush ozone treatment at 30-min intervals for 5 h in the presence of 2 kg wheat, with an initial ozone concentration of 13.9 mg/L. Toxicity data for empty space ozone treatments indicated a remarkable difference in susceptibility between the life stages of E. kuehniella and T. confusum. For E. kuehniella, empty space ozone treatment resulted in complete mortality of adults, pupae and larvae, while only 62.5% of the eggs were killed. For T. confusum, ozone treatment resulted in very low mortality of adults, pupae and eggs, ranging from 4.2 to 14.1% while only larvae had a high mortality (74%). Generally T. confusum was more tolerant to ozone treatment than E. kuehniella. Ozone flush treatment at 30-min intervals for 5 h resulted in almost complete mortality of all life stages of E. kuehniella placed in the top position of 2 kg wheat, whereas eggs of E. kuehniella placed in the bottom position of 2 kg wheat were hard to kill. For T. confusum, larvae placed in the bottom position of 2 kg wheat were easily killed, whereas eggs, pupae and adults survived.