CPR63 promotes pyrethroid resistance by increasing cuticle thickness in Culex pipiens pallens

The cuticle protein (CP) encoded by CPR63 plays a role in deltamethrin resistance in Culex pipiens pallens. Herein, we investigated the distribution of CPR63 transcripts in this organism and observed high expression levels in legs and wings. Furthermore, expression of CPR63 in the legs of deltamethrin-resistant (DR) strains was 2.17-fold higher than in deltamethrin-susceptible (DS) strains. Cuticle analysis of small interfering RNA (siRNA) groups by scanning electron microscopy (SEM) revealed a significantly thinner cuticle of the tarsi in the siCPR63 group than in the siNC (negative control siRNA) group. Transmission electron microscopy (TEM) revealed that the exocuticle and endocuticle thickness of the tarsi were significantly thinner, which contributes the thinner procuticle of tarsi in the siCPR63 group than in the siNC group. Our results suggested that CPR63 might contribute to the resistance phenotype by thickening the cuticle and thereby possibly increasing the tolerance of mosquitoes to deltamethrin.