EFFECTS OF HOST PLANT ON CARBOXYLESTERASE ACTIVITY IN COTTON APHID APHIS GOSSYPII GLOV.
GAO XI-WU(Department of Plant Protedtion. Beijing Agricultural University, Beijing 100084)
Experiments have shown that carboxylesterase activity nf the cotton aphid. Aphis gossypit Glov., varied with the varieties of its host plant. In the 7 cotton varieties tested, the esterase activity of aphids feeding on Chinese cotton 12 was the highest, as revealed in the hydrolysis tests with α-naphthyl acetate (α-NA) by individual aphid homogenate according to the method of Zheng (1989). It was approximately 6 times that of the aphids feeding on Jingyang Chicken Feet cotton. The esterase activity of the aphids feeding on Fangying Shuangwu cotton was the highest as shown in the hydrolysis tests with β-NA, about 5 times that of the aphids feeding on BR-S-10 cotton. In the aphids feeding on Fangying Shuangwu cotton, the proportion of individuals whose esterase activity exceeded 2.5μm/mg protein-minute was 28.3% with α-NA and 67.1% with β-NA, but in the aphids feeding on BR-S-10 cotton, only 2.6% with α-NA and 1.3% with β-NA. The ratio of esterase activities with α-NA and β-NA in the aphids feeding on Chinese cotton 12 was 0.79, but the ratios in the aphids feeding on other 6 cotton varieties were-over 1.0. The percentage of individuals whose α-NA and β-NA esterase activities were all less than the average of esterase activity was 26% in the aphids feeding on Chinese cotton 12, but 49-64% in the aphids feeding on other cotton varieties. The percentage of individuals whose α-NA and β-NA esterase activities were above the average was 19% in the aphids feeding on Chinese cotton 12 and 23-47% in the other groups. The proportions of individuals whose α-NA esterase activity was over the average, but P-NA esterase activity below the average, and whose α-NA estemse activity below the average but p-NA esterase over the average were 31% and 24% in aphids feeding on Chinese cotton 12, but only 0-76% and 3.4-10.4% in the aphids. feeding on other cotton varieties, respectively. All these data suggest that host plant varieties affected the carboxylesterase activity in cotton aphids.