Abstract: Culex quinquefasciatus, the major vector of the disease filariasis in China, is resistant to organophosphorus insecticides with an 8.12-fold resistance ratio at the LC₅₀ for parathion, and a high heterogeneity factor in wild populations. The main mechanism of resistance in this species is amplification of nonspecific esterases. Most resistant Culex quinquefasciatus mosquitoes have co-amplified est α2 and est β2 genes. Southern and dot blot analysis can be used to roughly quantify the est gene copy number in mosquitoes using probe hybridization and auoradiography. In addition, we measured gene and mRNA copy numbers using realtime PCRs. This accurate quantitative approach (fluorescent microvolume PCR) was performed to assess the specific expression profiles of est α and est β genes. The cDNA product of thePCR reaction was 500 base pairs long for the esterase α gene and 418 base pairsfor the β gene. The predicted protein alignment for the esterase β fragment had high homology with Culex pipiens esterase β1 (98%), Culex quinquefasciatus β2 (100%) and Culex tarsalis esterase β3 (90%). The gene copy number differed between individuals for the α and β genes, as well as between populations of Shanghai and PellRR mosquitoes from Sri Lanka, in which both the esterase α2 and β2 are involved in insecticide resistance.

Key words: Culex quinquefasciatus, organophosphorus insecticide resistance, gene amplification, gene copy number, quantitative PCR