A new allele conferring resistance to Lysinibacillus sphaericus is detected in low frequency in Culex quinquefasciatus field populations

Background The Cqm1 α-glucosidase of Culex quinquefasciatus larvae acts as the midgut receptor for the binary toxin of the biolarvicide Lysinibacillus sphaericus. Mutations within the cqm1 gene can code for aberrant polypeptides that can no longer be properly expressed or bind to the toxin, leading to insect resistance. The cqm1REC and cqm1REC-2 alleles were identified in a laboratory selected colony and both displayed mutations that lead to equivalent phenotypes of refractoriness to L. sphaericus. cqm1REC was first identified as the major resistance allele in this colony but it was subsequently replaced by cqm1REC-2, suggesting the better adaptive features of the second allele. The major aim of this study was to evaluate the occurrence of cqm1REC-2 and track its origin in field populations where cqm1REC was previously identified.