title: Detection of an allele conferring resistance to Bacillus sphaericus binary toxin in Culex quinquefasciatus populations by molecular screening.
abstract: The activity of the Bacillus sphaericus binary (Bin) toxin on Culex quinquefasciatus larvae depends on its specific binding to the Cqm1 receptor, a midgut membrane-bound alpha-glucosidase. A 19-nucleotide deletion in the cqm1 gene (cqm1(REC)) mediates high-level resistance to Bin toxin. Here, resistance in nontreated and B. sphaericus-treated field populations of C. quinquefasciatus was assessed through bioassays as well as a specific PCR assay designed to detect the cqm1(REC) allele in individual larvae. Resistance ratios at 90% lethal concentration, gathered through bioassays, were close to 1 and indicate that the selected populations had similar levels of susceptibility to B. sphaericus, comparable to that of a laboratory colony. A diagnostic PCR assay detected the cqm1(REC) allele in all populations investigated, and its frequency in two nontreated areas was 0.006 and 0.003, while the frequency in the B. sphaericus-treated population was significantly higher. Values of 0.053 and 0.055 were detected for two distinct sets of samples, and homozygote resistant larvae were found. Evaluation of Cqm1 expression in individual larvae through alpha-glucosidase assays corroborated the allelic frequency revealed by PCR. The data from this study indicate that the cqm1(REC) allele was present at a detectable frequency in nontreated populations, while the higher frequency in samples from the treated area is, perhaps, correlated with the exposure to B. sphaericus. This is the first report of the molecular detection of a biolarvicide resistance allele in mosquito populations, and it confirms that the PCR-based approach is suitable to track such alleles in target populations.
authors.affiliation: Department of Entomology, Centro de Pesquisas Aggeu Magalhães/FIOCRUZ, Av. Moraes Rego s/n, Cidade Universitária, Recife-PE 50670-420, Brazil.
authors.forename: Karlos Diogo de Melo
authors.initials: KD
authors.lastname: Chalegre
authors.forename: Tatiany Patrícia
authors.initials: TP
authors.lastname: Romão
authors.forename: Liliane Barbosa
authors.initials: LB
authors.lastname: Amorim
authors.forename: Daniela Bandeira
authors.initials: DB
authors.lastname: Anastacio
authors.forename: Rosineide Arruda
authors.initials: RA
authors.lastname: de Barros
authors.forename: Cláudia Maria Fontes
authors.initials: CM
authors.lastname: de Oliveira
authors.forename: Lêda
authors.initials: L
authors.lastname: Regis
authors.forename: Osvaldo Pompílio
authors.initials: OP
authors.lastname: de-Melo-Neto
authors.forename: Maria Helena Neves Lobo
authors.initials: MH
authors.lastname: Silva-Filha
mesh_terms: D000483:Alleles; D000818:Animals; D001427:Bacterial Toxins / Q000633:toxicity*; D003465:Culex / Q000187:drug effects* / Q000235:genetics*; D004351:Drug Resistance; D005787:Gene Frequency; D017344:Genes, Insect; D006720:Homozygote; D007113:Immunity, Innate; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction / Q000379:methods; D017384:Sequence Deletion; D000520:alpha-Glucosidases / Q000235:genetics* / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D019476:Insect Proteins; C046134:binB protein, Bacillus sphaericus; D000520:alpha-Glucosidases