Medical and Veterinary Entomology (2002) 16, 99-105

D. De Silva and J. Hemingway (2002)
Structural organization of the est_alpha3¹ gene in a Colombian strain of Culex quinquefasciatus differs from that in Cuba
Medical and Veterinary Entomology 16 (1), 99-105
Abstract: In Culex mosquitoes (Diptera: Culicidae), the most common mechanism for resistance to organophosphorus (OP) insecticides involves amplification of one or more esterases. Two esterase loci are often involved, with different allelic forms co-amplified. Est_alpha3¹ is co-amplified with estß1 in a Colombian (COL) strain of Culex quinquefasciatus Say. These two alleles co-migrate on acrylamide gels, often leading to misscoring of the phenotype as elevation of a single estß enzyme. By sequencing COL genomic DNA, we determined the est_alpha3¹ gene length is 1623 nucleotides. The open reading frame of est_alpha3¹ encodes a 540 amino acid protein, as for est_alpha2¹ in strain Pel RR from Sri Lanka. The intron/exon boundaries of est_alpha3¹ are identical to those of est_alpha2¹, suggesting that they are alleles of the same locus. The COL est_alpha3¹ gene differs from est_alpha3² in strain MRES from Cuba, although they have equivalent electrophoretic mobility, showing that these two strains contain distinct resistance-associated amplicons. Twenty nucleotide differences were scored between the MRES partial 495 bp sequence and that in the COL strain, with two amino acid changes, demonstrating distinct estalpha enzymes. Our sequencing data show 95% identity between the three estalpha genes (each has six introns and seven exons) in OP-resistant Cx. quinquefasciatus. Amplified est_alpha3¹ and estß1 are at least 10 kb apart in temephos-selected COL and 2.7 kb apart in Pel RR, whereas these non-amplified genes are only 1.7 kb apart in the non-selected parental COL stock, as in Pel SS (susceptible Sri Lankan strain), demonstrating that this region of the genome is susceptible to expansion and contraction.
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Link to article at publishers website
Database assignments for author(s): Janet Hemingway

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest
molecular biology - genes

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Culex quinquefasciatus		Sri Lanka
	Culex quinquefasciatus		Cuba
	Culex quinquefasciatus		Colombia