Biochemical mechanism of resistance of cotton aphids to organophosphorus insecticides.

Abstract

The cotton aphid Aphis gossypii Glover is oue of the most important pests infesting cotton in the cotton areas of North China. Since 1953 organophosphorus insecticides have been used to-control the aphid for keeping up good yield of cotton. At present, resistance of the aphid to insecticides has become a vital probl閙 in cotton production. This has prompted us to investi-gata the mechanism of resistance to organophosphorus insecticides and to search for the strategy to control the resistant aphids.All experiments were performed on apterous viviparous female aphids and topical applica-tion was adopted for testing the effct of insecticides on the aphids. Three populations of cot-ton aphids (B-Beijing, Q = Qing Dao, and G = Gao Mi) were compared. The LD50 values of parthion and paraoxon on aphids of population B, Q and G were 38 and 4, 59 and 9, and 93,5 and 21 ng/aphid respectively. Besides the slower penetration of organophosphorus insecticides into the aphids of resistant populations, the use of synergists including methyl iodide, SV1 (O, O-diethyl O-phenyl phosphorothionate) and piperonyl bul oxide has given evidence indica-ting whether mixed function oxidases (MFO), carboxylcsterase and glutathion S-transferase are involved in the formation of resistance. MFO seems to be one of the factors causing resistance, but the cotton aphid homogenates in v韙ro are found to contain endogenous inhibitors of MFO. The results also showed that the sensitivity of AChE to paraoxon in resistant population G was 1.9 and 14.2 times lowcr than that in populations Q and B. The activities of L-Na este-rases and L-NA carboxylesterases in population G were respectively 2.3-15.4 and 18.0-70.0 times higher than that in populations Q and B. The activities of esterases showed rnore conspi-cuous difference in the three populations.