Molecular and biological features of Culex quinquefasciatus homozygous larvae for two cqm1 alleles that confer resistance to Lysinibacillus sphaericus larvicides.

BACKGROUND: Culex quinquefasciatus resistance to the binary toxin from Lysinibacillus sphaericus larvicides can occur because of mutations in the cqm1 gene that prevents the expression of the toxin receptor, Cqm1 α-glucosidase. In a resistant laboratory-selected colony maintained for more than 250 generations, cqm1REC and cqm1REC-2 resistance alleles were identified. The major allele initially found, cqm1REC , became minor and was replaced by cqm1REC-2 . This study aimed to investigate the features associated with homozygous larvae for each allele to understand the reasons for the allele replacement and to generate knowledge on resistance to microbial larvicides. RESULTS: Homozygous larvae for each allele were compared. Both larvae displayed the same level of resistance to the binary toxin (3500-fold); therefore, a change in phenotype was not the reason for the replacement observed. The lack of Cqm1 expression did not reduce the total specific α-glucosidase activity for homozygous cqm1REC and cqm1REC-2 larvae, which were statistically similar to the susceptible strain, using artificial or natural substrates. The expression of eight Cqm1 paralog α-glucosidases was demonstrated in resistant and susceptible larvae. Bioassays in which cqm1REC or cqm1REC-2 homozygous larvae were reared under stressful conditions showed that most adults produced were cqm1REC-2 homozygous (69%). Comparatively, in the offspring of a heterozygous sub-colony reared under optimal conditions for 20 generations, the cqm1REC allele assumed a higher frequency (0.72). CONCLUSION: Homozygous larvae for each allele exhibited a similar resistant phenotype. However, they presented specific advantages that might favor their selection and can be used in designing resistance management practices. © 2021 Society of Chemical Industry.

Zika virus replication in the mosquito Culex quinquefasciatus in Brazil.

Zika virus (ZIKV) is a flavivirus that has recently been associated with an increased incidence of neonatal microcephaly and other neurological disorders. The virus is primarily transmitted by mosquito bite, although other routes of infection have been implicated in some cases. The Aedes aegypti mosquito is considered to be the main vector to humans worldwide; however, there is evidence that other mosquito species, including Culex quinquefasciatus, transmit the virus. To test the potential of Cx. quinquefasciatus to transmit ZIKV, we experimentally compared the vector competence of laboratory-reared Ae. aegypti and Cx. quinquefasciatus. Interestingly, we were able to detect the presence of ZIKV in the midgut, salivary glands and saliva of artificially fed Cx. quinquefasciatus. In addition, we collected ZIKV-infected Cx. quinquefasciatus from urban areas with high microcephaly incidence in Recife, Brazil. Corroborating our experimental data from artificially fed mosquitoes, ZIKV was isolated from field-caught Cx. quinquefasciatus, and its genome was partially sequenced. Collectively, these findings indicate that there may be a wider range of ZIKV vectors than anticipated.