Synergism and efficacy of sulfur dioxide plus carbon dioxide fumigation for control of stored product insects.

Sulfur dioxide (SO2) fumigations with and without CO2 were conducted in 1.9 L jars at 21 °C to determine synergism against rice weevil (Sitophilus oryzae) adults and confused flour beetle (Tribolium confusum) adults. Large-scale fumigations of 25 kg wheat in a 60 L chamber with SO2 plus 10% CO2 were conducted using an automated injection system based on SO2 concentration to demonstrate efficacy against all life stages of 3 stored product insects: confused flour beetle, granary weevil (Sitophilus granarius), and rice weevil. There was strong synergism between CO2 and SO2 against rice weevil adults and synergism was stronger at lower SO2 concentrations. Strong synergism between SO2 and 10% CO2 was also demonstrated against confused flour beetle adults with only 6.67% mortality for 428 ppm SO2 alone and 94.33% mortality for 344 ppm SO2 plus 10% CO2 in 24-h fumigations. In large-scale 24-h fumigations with 2,400 to 2,800 ppm SO2 of wheat grains under 10% CO2 atmospheres at 21 °C, complete control of adults of all 3 stored product insects were achieved. Over 95% and 99% mortalities were achieved against immature stages of confused flour beetle and the 2 weevil species, respectively. The synergistic effects of CO2 with SO2 and the system to maintain effective SO2 concentrations demonstrated in this study suggest that SO2 fumigation under CO2 enriched atmosphere has good potential for practical applications to control stored product insects.