Detection of an allele conferring resistance to Bacillus sphaericus binary toxin in Culex quinquefasciatus populations by molecular screening.
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.
Chalegre
Karlos Diogo de Melo
KD
Department of Entomology, Centro de Pesquisas Aggeu Magalhães/FIOCRUZ, Av. Moraes Rego s/n, Cidade Universitária, Recife-PE 50670-420, Brazil.
Romão
Tatiany Patrícia
TP
Amorim
Liliane Barbosa
LB
Anastacio
Daniela Bandeira
DB
de Barros
Rosineide Arruda
RA
de Oliveira
Cláudia Maria Fontes
CM
Regis
Lêda
L
de-Melo-Neto
Osvaldo Pompílio
OP
Silva-Filha
Maria Helena Neves Lobo
MH
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
D001427:Bacterial Toxins; D019476:Insect Proteins; C046134:binB protein, Bacillus sphaericus; D000520:alpha-Glucosidases