| Summary: | <p>Abstract</p> <p>Background</p> <p>Analysis of <it>Culex pipiens</it> mosquitoes collected from a single site in Lebanon in 2005, revealed an alarming frequency of <it>ace-1</it> alleles conferring resistance to organophosphate insecticides. Following this, in 2006 the majority of municipalities switched to pyrethroids after a long history of organophosphate usage in the country; however, since then no studies have assessed the impact of changing insecticide class on the frequency of resistant <it>ace-1</it> alleles in <it>C. pipiens</it>.</p> <p>Methods</p> <p><it>C. pipiens</it> mosquitoes were captured indoors from 25 villages across the country and subjected to established methods for the analysis of gene amplification at the <it>Ester</it> locus and target site mutations in <it>ace-1</it> gene that confer resistance to organophosphates.</p> <p>Results</p> <p>We conducted the first large-scale screen for resistance to organosphosphates in <it>C. pipiens</it> mosquitoes collected from Lebanon. The frequency of carboxylesterase (<it>Ester</it>) and <it>ace-1</it> alleles conferring resistance to organophosphates were assessed among <it>C. pipiens</it> mosquitoes collected from 25 different villages across the country between December 2008 and December 2009. Established enzymatic assay and PCR-based molecular tests, both diagnostic of the major target site mutations in <it>ace-1</it> revealed the absence of the F290V mutation among sampled mosquitoes and significant reduction in the frequency of G119S mutation compared to that previously reported for mosquitoes collected from Beirut in 2005. We also identified a new duplicated <it>ace-1</it> allele, named <it>ace-1</it><sup><it>D13</it></sup>, exhibiting a resistant phenotype by associating a susceptible and a resistant copy of <it>ace-1</it> in a mosquito line sampled from Beirut in 2005. Fisher’s exact test on <it>ace-1</it> frequencies in the new sample sites, showed that some populations exhibited a significant excess of heterozygotes, suggesting that the duplicated allele is still present. Starch gel electrophoresis indicated that resistance at the <it>Ester</it> locus was mainly attributed to the <it>Ester</it><sup><it>2</it></sup> allele, which exhibits a broad geographical distribution.</p> <p>Conclusions</p> <p>Our analysis suggests that the frequency of resistant <it>ace-1</it> alleles in mosquito populations can be downshifted, and in certain cases (F290V mutation) even eliminated, by switching to a different class of insecticides, possibly because of the fitness cost associated with these alleles.</p>
|
|---|
