Effect of Reduced Pressure and CO2 on the Toxicity of Methyl Bromide to Two Species of Stored-Product Insects1

Abstract

The combination of methyl bromide with either CO2 or reduced pressure (100 mm of Hg (absolute pressure)), or both, was tested against adult Tribolium castaneum (Herbst) and Sitophilas oryzae (L.) adults. The combinations increased the susceptibility of T. castaneum to methyl bromide by 1.6-fold. Their susceptibility to the combination of methyl bromide with both CO2 and reduced pressure was increased by ca. 2-fold at the LD50 but the LD95 was similar to those of the other treatments. Combining methyl bromide with 20% CO2 increased the susceptibility of adult S. oryzae to methyl bromide by 1.5-fold; the combination of methyl bromide with pressure reduced to 100 mm of Hg produced a response curve such that the LD50 of methyl bromide was lowered by ca. 4-fold, but the LD95 was not significantly different than the response to either methyl bromide alone or methyl bromide with 20% CO2, The combination of 20% CO2 with pressure reduced to 100 mm of Hg without methyl bromide produced 60% mortality of S. oryzae adults. Apparently, reduced pressure altered the mode of action of CO2 or methyl bromide against S. oryzae .