Title: Selection and characterization of temephos resistance in a population of Aedes aegypti from Tortola, British Virgin Islands Wirth MC, Georghiou GP Ref: J Am Mosq Control Assoc, 15:315, 1999 : PubMed
A collection of Aedes aegypti from Tortola, British Virgin Islands, with a high level of temephos resistance (46.8-fold at the 95% lethal concentration [LC95]) was selected to higher resistance with temephos in the laboratory. After 13 generations of pressure, the temephos resistance ratio increased to 180.6 (LC95), whereas in the absence of selection pressure the resistance ratio declined to 8.5. Relatively low levels of resistance or cross-resistance to other organophosphate and carbamate insecticides, and a high level of resistance to the pyrethroid permethrin were also observed. Synergism tests implicated detoxifying esterases in temephos resistance and the presence of elevated esterase activity was confirmed by biochemical tests; however, no evidence was found of insensitive acetylcholinesterase. Mendelian crosses indicated that temephos resistance was inherited as a monofactorial trait. The presence of high levels of temephos and permethrin resistance in Ae. aegypti has important implications for Aedes control programs.
Title: Isolation and characterization of two novel organophosphate resistance mechanisms in Culex Pipiens from Cyprus Wirth MC Ref: J Am Mosq Control Assoc, 14:397, 1998 : PubMed
Two novel mechanisms of organophosphate resistance were isolated and characterized from a population of Culex pipiens L. from Cyprus. Two strains, one expressing the novel, highly active esterases A5 and B5 (strain A5B5-R), and one expressing insensitive acetylcholinesterase (strain Ace-R), were developed by single pair crosses and selection with temephos and propoxur, respectively. The A5B5-R strain demonstrated resistance toward organophosphate insecticides that could be suppressed by the esterase inhibitor S,S,S-tributyl 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 by the monooxygenase inhibitor piperonyl butoxide or by DEF. The Ace-R strain possessed a novel toxicologic profile as well as a unique acetylcholinesterase inhibition pattern. Inheritance of temephos or propoxur resistance was codominant in F1 offspring. Backcrosses to a susceptible strain in both cases failed to fit a single gene model, suggesting that multiple loci may be involved. Combining the A5B5-R and the Ace-R strains resulted in high levels of temephos resistance, similar to that of the parents.
Title: Organophosphate resistance in Culex pipiens from Cyprus Wirth MC, Georghiou GP Ref: J Am Mosq Control Assoc, 12:112, 1996 : PubMed
Populations of Culex pipiens were sampled from 8 locations in Cyprus between 1987 and 1993. All population samples generally revealed organophosphate resistance to malathion, temephos, chlorpyrifos, fenthion, dichlorvos, and pirimiphos methyl, in decreasing order of magnitude. Of 7 populations assessed with the carbamate propoxur, all proved to be resistant to different degrees. Of the 6 populations tested with permethrin, 2 were resistant to permethrin. Resistance was associated with the presence of 5 different overproduced esterases (esterases A1, A2, A5, B2, and B5) as well as an insensitive form of acetylcholinesterase. These results are discussed in relation to the ongoing mosquito abatement program in Cyprus and to similar programs in other parts of the world.
Title: Esterases A2 and B2 in Culex quinquefasciatus (Diptera: Culicidae): role in organophosphate resistance and linkage Wirth MC, Marquine M, Georghiou GP, Pasteur N Ref: Journal of Medical Entomology, 27:202, 1990 : PubMed
Two highly active esterases, A2 and B2, were isolated in SeLax, a strain of Culex quinquefasciatus Say from California which demonstrated resistance levels of 19, 14, and 4.3 times to the organophosphate insecticides chlorpyrifos, temephos, and malathion, respectively. Selection of SeLax by temephos during 31 generations increased resistance to this insecticide to 65 times. This resistance was shown to be DEF-suppressible, monofactorial, and strongly associated with the presence of esterases A2 and B2. Although these two esterases are encoded by distinct structural genes, no disjunction was observed when SeLax was crossed to S-Lab, a susceptible strain, or to S54, a strain resistant to organophosphates by means of esterase A1. However, when SeLax was crossed to strain Tem-R, which is resistant to organophosphates because of a highly active esterase B1, all possible recombinants occurred. These results were discussed in relation to the recent discovery that increased activity of B esterases in the genus Culex is caused by gene amplification.
