Effect of Atmospheric Gases Alone or in Combination on the Mortality of Granary and Rice Weevils1

The time required to obtain 50 and 95% mortality of the granary weevil, Sitophilus granarius (L.), and the rice weevil, S. oryzae (L.), in atmospheres of CO2, N2, or He and in various combinations of CCvair and CO2-O2 was determined. The order of susceptibility of granary and rice weevil adults in CO2, N2, or He atmospheres was 80° > 70° > 60°F. Granary weevil adults were the most susceptible stage to atmospheres of CO2, N2, or He, followed by larvae, pupae, and eggs. Rice weevil adults were the most susceptible stage to atmospheres of CO2, N2 or He, followed by larvae, eggs, and pupae. CO2 concentrations of 90–40% in air were more toxic to rice weevil adults than 100% CCy Concentrations of 90–60% CO2 in air were more toxic to granary weevil adults than 100% CO2. The time required for 50 or 95% kill of granary weevil adults was about the same whether exposed to various CO2-air or CO2-O2 combinations, and a similar response was obtained for rice weevil adults.