SYNERGISM OF METHYL-BROMIDE AND SULFURYL FLUORIDE TOXICITY AGAINST TERMITES (ISOPTERA, KALOTERMITIDAE, RHINOTERMITIDAE) BY ADMIXTURE WITH CARBON-DIOXIDE

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 a ccumulated doses (LAD, 20-h exposure) of methyl bromide for 99% mortal ity against I. snyderi were 50, 37, 28, and 28 mg . h/liter and, for s ulfuryl fluoride, 45, 30, 30, and 33 mg . h/liter at 0, 5, 10, and 20% CO2 (vol:vol), respectively. LAD(99) values against C. formosanus wit h methyl bromide were 38, 32, 24, and 24 mg . h/liter and, for sulfury l 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 methy l bromide against I. snyderi more than against C. formosanus, whereas CO2 increased the toxicity of sulfuryl fluoride against C. formosanus more than against I. snyderi. Based on LAD(99) values against I. snyde ri, a maximum synergism ratio (SR) of 1.8 was induced by CO2 in admixt ure with methyl bromide at 10 or 20% CO2. For C. formosanus, a maximum SR of 2.2 was attained with 10% CO2 when combined with sulfuryl fluor ide. These results indicate that the application rates of structural f umigants may be reduced by the simultaneous addition of 10% CO2 into f umigated airspace.