Synergism of Methyl Bromide and Sulfuryl Fluoride Toxicity Against Termites (Isoptera: Kalotermitidae, Rhinotermitidae) by Admixture with Carbon Dioxide

Abstract

Toxicities of methyl bromide and sulfuryl fluoride in combination with CO2 were assessed against pseudergates of Incisitermes snyderi (Light) and workers of Coptotermes formosanus Shiraki. Estimates of lethal accumulated doses (LAD, 20-h exposure) of methyl bromide for 99% mortality against l. snyderi were 50, 37, 28, and 28 mg-h/liter and, for sulfuryl fluoride, 45, 30, 30, and 33 ingh/liter at 0, 5, 10, and 20% CO2 (vol:vol), respectively. LAD99 values against C. formosanus with methyl bromide were 38, 32, 24, and 24 mg-h/liter and, for sulfuryl fluoride, 45, 29, 20, and 28 mg-h/liter at 0, 5, 10, and 20% CO2 (vol:vol), respectively. In general, CO2 enhanced the toxicity of methyl bromide against l. snyderi more than against C. formosanus, whereas CO2 increased the toxicity of sulfuryl fluoride against C. formosauns more than against I. snyderi. Based on LAD99 values against I. snyderi, a maximum synergism ratio (SR) of 1.8 was induced by CO2 in admixture with methyl bromide at 10 or 20% CO2, For C. fomuosanus, a maximum SR of 2.2 was attained with 10% CO2 when combined with Sulfury fluoride. These results indicate that the application rates of structural fumigants may Be reduced by the simultaneous addition of 10% CO2 into fumigated airspace.