Suppression of α-glucosidase gene by RNA interference can increase resistance ofCulex quinquefasciatustoBacillus sphaericusbinary toxin

Bacillus sphaericus binary toxin displays a specific toxicity towards Culex spp. larvae. Resistance of Culex quinquefasciatus to B. sphaericus is associated with the reduction or absence of 66-kDa α-glucosidase, a binary toxin receptor, in larval midgut microvilli. In this study, long double-stranded RNA (dsRNA) targeting the α-glucosidase gene was used to suppress the expression of α-glucosidase in Cx. quinquefasciatus larvae and the consequences of the suppression was investigated. Three sets of dsRNAs, dsGRi1, dsGRi2, and dsGRi3, which are homologous to distinct regions of α-glucosidase gene, were delivered to mosquito larva by feeding with dsRNA–chitosan particles. Reverse transcriptase-polymerase chain reaction results demonstrated that the expression of α-glucosidase mRNA was reduced by 43% in larvae fed with dsGRi3–chitosan, compared to those fed with dsgfp–chitosan particles. Western blot analysis revealed a 7–17% reduction of α-glucosidase protein expression in larvae fed with dsGRi–chitosan. Mortality rates of larvae that received dsRNAs–chitosan particles were only 45–62% compared to those that received dsgfp–chitosan particles. These results indicate that α-glucosidase is essential for the toxicity of B. sphaericus binary toxin to Cx. quinquefasciatus.