Effects of High-CO2 Fumigation on Sitophilus granarius (L.) Life Stages in Wheat Under Different Temperatures and Exposure Durations.

Sitophilus granarius (L.) is a major primary pest of stored grain worldwide. This study evaluated the efficacy of 100% CO2 against adults and immature stages (eggs, larvae, and pupae) of S. granarius at 25 °C (optimal temperature) and 37 °C (sublethal thermal stress) after three, six, 12, and 21 days of exposure. Both CO2 and temperature significantly affected insect survival, although susceptibility, evaluated as the suppression of adult emergence for immature stages, differed among life stages. While treatment with 100% CO2 achieved complete adult mortality within three days at both temperatures, exposure to 37 °C alone induced 100% mortality within 12 days. Eggs were the most susceptible immature stage: 100% CO2 completely prevented adult emergence after 12 days at 25 °C and three days at 37 °C, while exposure to 37 °C alone was sufficient to inhibit emergence. In contrast, neither larval- nor pupal-infested wheat showed complete suppression of adult emergence following CO2 treatment. At 25 °C, CO2 significantly reduced adult emergence from both stages at all exposure durations, whereas at 37 °C significant reductions were detected only after three days, as thermal stress alone had already markedly reduced emergence. These findings demonstrate that exposure to 100% CO2 alongside sublethal thermal stress provides an overall increase in mortality across life stages, although larvae and pupae remain substantially more tolerant than adults and eggs.