Isolation and characterization of two novel organophosphate resistance mechanisms in Culex pipiens from Cyprus

Two novel mechanisms of organophosphate resistance were isolated and charac terized from a population of Culex pipiens L. from Cyprus. Two strains, one expressing the novel, highly active esterases A5 and B5 (strain A5B5-R), a nd one expressing insensitive acetylcholinesterase (strain Ace-R), were dev eloped by single pair crosses and selection with temephos and propoxur, res pectively. The A5B5-R strain demonstrated resistance toward organophosphate insecticides that could be suppressed by the esterase inhibitor S,S,S-trib utyl phosphorotrithioate (DEF). No cross-resistance to carbamates occurred. The Ace-R strain demonstrated resistance to organophosphate as well as to carbamate insecticides. Propoxur and temephos resistance was not affected b y the monooxygenase inhibitor piperonyl butoxide or by DEE The Ace-R strain possessed a novel toxicologic profile as well as a unique acetylcholineste rase inhibition pattern. Inheritance of temephos or propoxur resistance was codominant in F-1 offspring. Backcrosses to a susceptible strain in both c ases failed to fit a single gene model, suggesting that multiple loci may b e involved. Combining the A5B5-R and the Ace-R strains resulted in high lev els of temephos resistance, similar to that of the parents.