Amplified esterases B1 and A2-B2 in field populations of Culex pipiens from China

The main organophosphate (OP) resistance mechanism in the Culex pipiens com plex is increased activity of esterases A and B. Fourth-stage larvae from 2 field populations of C. pipiens from Gaomi and Kunming, China, were compar ed for tolerance to parathion, dichlorovos (OP), and bassa (carbamate) inse cticides. Both populations were resistant to OPs but not to bassa. Starch g el electrophoresis indicated that elevated esterase activity was correlated with OP resistance. High frequencies of amplified esterase genes B1 and A2 -B2 (0.85 and 0.50) were discovered in Gaomi and Kunming, respectively. How ever, only low levels of gene amplification were detected.