Effect of methyl bromide fumigation combined with carbon dioxide on Tetranychus cinnabarinum(acari: tetranychidae)

At 25℃, Tetranychus cinnabarinus was fumigated with methyl bromide alone at 20, 25, 30, 35 and 40 g/m~3 or in combination with CO_2 at 10%, 15%, 20%, 30% or 40%. Treatment duration being identical,fumigation toxicity increased with methyl bromide dosage and LD_(50)s were 27.8288,21.4533 and 16.0683 g/m~3,respectively,for 1,1.5 and 2 h fumigating.With the same dosage of methyl bromide,the mortality of the pest increased with CO_2 concentration to its maximum,followed by a decline.Combination of methyl bromide at 40 g/m~3 with 25% CO_2 gave the best result with a mortality rate of 100% for 2 h fumigating,suggesting that CO_2 could have a synergistic effect.Owing to a narcotism of CO_2 to the mite,toxicity of fumigation decreased when fumigation time was less than 1 h or when CO_2 was greater than 30%.