Affiliation:
1. Department of Entomology
2. Department of Microbiology, Centro de Pesquisas Aggeu Magalhães/FIOCRUZ, Recife-PE 50670-420, Brazil
Abstract
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 α-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 α-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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
25 articles.
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