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Aedes albopictus , a common mosquito in Zhejiang Province, is a carrier of more than twenty arboviruses. There are dozens or even hundreds of imported cases of dengue fever every year in Zhejiang Province, and there have also been many local outbreaks caused by imported cases of dengue fever. The objectives were to assess the resistance of larvae and adults of several Ae. albopictus strains in Zhejiang Province to commonly used pyrethroid insecticides (beta-cypermethrin, deltamethrin and permethrin), and detect mutations in the sodium channel gene, to further analyse the relationship between phenotypic resistance and the frequency of mutations. The resistance of eight field strains of Ae. albopictus larvae to beta-cypermethrin, deltamethrin and permethrin ranged from 8.17 to 36.06, 12.12–107.3 and 1.55–81.9, respectively, and there was a significant positive correlation of interaction resistance among the three insecticides. The mutation frequencies of I1532T and F1534S in the larvae of Ae. albopictus were 0–6.25 % and 42.19–100.00 %. Moreover, the diagnostic doses of the three pyrethroids for adult Ae. albopictus mosquitoes were 0.2510 g/L, 0.1562 g/L, and 0.9072 g/L. Except for the Zhoushan strain, which was suspected to be resistant to beta-cypermethrin, the other field strains were resistant to the three pyrethroids, and there was a significant positive correlation of cross-resistance among the three insecticides. The mutation frequencies of I1532T and F1534S of adult Ae. albopictus were 0–1.56 % and 62.50–100.00 %. In addition, the LC 50 of the larvae and the mortality rate of adult Ae. albopictus after treatment with the three pyrethroids were significantly and positively correlated with the frequency of the F1534S mutation. F1534S mutation occurred earlier than I1532T mutation in both larvae and adult Ae. albopictus. F1534S mutation in the sodium channel gene may be a particular biomolecular detection marker for resistance to pyrethroid insecticides in Ae. albopictus in Zhejiang Province. • Phenotypic resistance of Ae. albopictus larvae and adults to pyrethroid insecticides are described. • The mutation order of the VGSC gene locus in Ae. albopictus is discussed. • The relationship between the frequency of VGSC gene mutation and phenotypic resistance in Ae. albopictus is discussed. [ABSTRACT FROM AUTHOR]

Summary Mosquitoes are hematophagous vectors that can acquire human viruses in their intestinal tract. Here, we define a mosquito gut commensal bacterium that promotes permissiveness to arboviruses. Antibiotic depletion of gut bacteria impaired arboviral infection of a lab-adapted Aedes aegypti mosquito strain. Reconstitution of individual cultivable gut bacteria in antibiotic-treated mosquitoes identified Serratia marcescens as a commensal bacterium critical for efficient arboviral acquisition. S. marcescens facilitates arboviral infection through a secreted protein named Sm Enhancin, which digests membrane-bound mucins on the mosquito gut epithelia, thereby enhancing viral dissemination. Field Aedes mosquitoes positive for S. marcescens were more permissive to dengue virus infection than those free of S. marcescens. Oral introduction of S. marcescens into field mosquitoes that lack this bacterium rendered these mosquitoes highly susceptible to arboviruses. This study defines a commensal-driven mechanism that contributes to vector competence, and extends our understanding of multipartite interactions among hosts, the gut microbiome, and viruses. Graphical Abstract Highlights • The gut commensal Serratia marcescens promotes mosquito permissiveness to arboviruses • S. marcescens facilitates arboviral infection via a secreted protein named Sm Enhancin • Sm Enhancin digests gut membrane-bound mucins to enhance viral dissemination in mosquitoes • S. marcescens enhances the susceptibility of field mosquitoes to dengue virus Wu et al. identified Serratia marcescens as a mosquito gut commensal bacterium critical for efficient arboviral acquisition. S. marcescens facilitates arboviral infection through secretion of a protein named Sm Enhancin. Colonization of S. marcescens in field-derived Aedes mosquitoes enhances vector competence. Gut residence of S. marcescens correlates with region-specific dengue prevalence. [ABSTRACT FROM AUTHOR]