Population‐specific gene expression patterns underlying differential sensitivity to deltamethrin in Culex pipiens in Blida Province, Northern Algeria

Abstract Insecticide resistance in mosquitoes poses a major challenge for vector control and the prevention of mosquito‐borne diseases. This study investigated resistance to the pyrethroid deltamethrin and associated gene expression responses in Culex pipiens Linnaeus, 1758 (Diptera: Culicibae) populations from Blida Province, Northern Algeria. Larvae were collected from two urban sites (Mouzaia and 13‐May) and one rural site (Hammam Melouane), and susceptibility bioassays were conducted using fourth‐instar larvae following WHO guidelines. Marked differences in susceptibility were observed among populations. The rural population was highly susceptible (LC 50 = 0.00002 ppm), whereas urban populations exhibited strong resistance, with resistance ratios reaching up to 1000‐fold. To explore underlying molecular responses, larvae were exposed to LC 25 , LC 50 , and LC 75 concentrations of deltamethrin, and expression of detoxification, mitochondrial, and digestive enzyme genes was quantified by reverse transcription real‐time PCR (RT‐qPCR). CYP6F1 expression was strongly associated with resistance in the highly resistant urban population, suggesting an important role in metabolic detoxification. In contrast, the susceptible rural population showed pronounced inducible expression of CYP6F1 , mitochondrial genes ( cytochrome b and COXI ), chymotrypsin , and acetylcholinesterase following insecticide exposure, indicating a generalized stress response. These findings reveal population‐specific physiological responses to deltamethrin and highlight the complex interplay between detoxification pathways, mitochondrial activity, and protease functions in shaping insecticide responses. The high resistance levels detected in urban populations underscore the need for continuous resistance monitoring and improved vector management strategies.