Efficacy of chlorine dioxide gas against five stored-product insect species

Abstract: In this study, the efficacy of chlorine dioxide gas as a potential fumigant to control stored-product insects was evaluated. Adults of five species of economically important stored-product insects were exposed for varying time periods to four concentrations of chlorine dioxide gas. Mortality was observed on days 1 through 5 after exposure to record any delayed mortality effects. Phosphine susceptible laboratory strains and phosphine resistant field strains of the five species were exposed to chlorine dioxide. The five species tested included the lesser grain borer, red flour beetle, sawtoothed grain beetle, rice weevil, and maize weevil. Exposure to 0.54 g/m3 (200 ppm) of chlorine dioxide for 8 h at an average temperature of 18 °C and an average humidity of 20% only resulted in less than 40% mortality of the five species. All exposed sawtothed grain beetles died within a day when exposed for 6 h to a chlorine dioxide concentration of 1.35 g/m3 (500 ppm). Red flour beetle, rice and maize weevils, and lesser grain borer were more tolerant to this concentration, with mortality ranging between 25 and 80%. An exposure to a chlorine dioxide concentration of 2.02 g/m3 (750 ppm) for 6 h produced trends in mortality of all five species that was similar to mortality observed at 500 ppm. The mortality of phosphine-susceptible and phosphine-resistant sawtoothed grain beetle, red flour beetle, and lesser grain borer adults was 100% mortality when exposed for 7 h to a chlorine dioxide concentration of 2.70 g/m3 (1000 ppm). Only the phosphine susceptible rice weevil showed 100% mortality at this concentration. Phosphine resistant rice weevil and maize weevil had 57 and 50% mortality when exposed for 7 h to a chlorine dioxide concentration of 2.70 g/m3. At this concentration and exposure time, phosphine susceptible maize weevil showed 83% mortality one day after exposure. The post-exposure mortality increased from day 1 to day 5 suggesting delayed mortality effects after exposure to chlorine dioxide. Chlorine dioxide may be a potential gas to control laboratory and field strains of the five species tested.