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The sensitivity of a susceptible and two resistant strains of cotton bollworm, Helicoverpa armigera, to phoxim, malathion and methomyl was determined by a topical application of bioassay method. YG strain, collected from field of Yanggu, Shandong Province of China, possessed 7-, 13- and 20-fold of resistance to the above three antiacetylcholinesterases based on the comparison of LD50 values with a laboratory susceptible strain. There were not significant difference of the specific activity and the Vmax value among the three strains. But the affinity of AChE to acetylthiocholine (ATCh), in YG strain was the lowest among the three strains tested. A cDNA encoding partial AChE gene was cloned from the three strains by RT-PCR and there was one nucleotide acid difference between YG strain and other two strains which resulted in no amino acid mutation. This partial AChE gene was used as a probe to perform Southern blot. The results indicated that there was no gene amplification in resistant cotton bollworm. Altered AChE with a decreased sensitivity to inhibitors appeared to be one of important resistance mechanisms in cotton bollworm against OP and carbamate compounds.
The sensitivity of a susceptible and two resistant strains of cotton bollworm, Helicoverpa armigera, to phoxim, malathion and methomyl was determined by a topical application of bioassay method. YG strain, collected from field of Yanggu, Shandong Province of China, possessed 7-, 13- and 20-fold of resistance to the above three anti acetylcholinesterases based on the comparison of LD50 values with a laboratory susceptible strain. There were not significant differences of the specific activity and the Vmax value among the three strains. But the affinity of AChE to acetylthiocholine (ATCh), in YG strain was the lowest among the three strains tested. A cDNA encoding partial AChE gene was cloned from the three strains by RT-PCR and there was one nucleotide acid difference between YG strain and other two strains which resulted in no amino acid mutation. This partial AChE gene was used as a probe to perform Southern blot. The results indicates that there was no gene amplification in resistant c otton bollworm. Altered AChE with decreased sensitivity to inhibitors was be be one of important resistance mechanisms in cotton bollworm against OP and carbamate compounds.