Cuticle Modifications and Over-Expression of the Chitin-Synthase Gene in Diflubenzuron-Resistant Phenotype

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 under-
pinning 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 mi-
croscopy, 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.