Insecticide resistance is a major threat challenging the control of harmful insect species. The study of resistant phenotypes is, therefore, pivotal to understand molecular mechanisms underpinning insecticide resistance and plan effective control and resistance management strategies. Here, we further analysed the diflubenzuron (DFB)-resistant phenotype due to the point-mutation I1043M in the chitin-synthase 1 gene (chs1) in the mosquito Culex pipiens. By comparing susceptible and resistant strains of Cx. pipiens through DFB bioassays, molecular analyses and scanning electron microscopy, we showed that the I1043M-resistant mosquitoes have: (i) a striking level of DFB resistance (i.e., resistance ratio: 9006); (ii) a constitutive 11-fold over-expression of the chs1 gene; (iii) enhanced cuticle thickness and cuticular chitin content. Culex pipiens is one of the most important vector species in Europe and the rapid spread of DFB resistance can threaten its control. Our results, by adding new data about the DFB-resistant phenotype, provide important information for the control and management of insecticide resistance.
