Insecticide resistance level and geographical distribution of target-site mutations in field collections of the house fly (Musca domestica) from Türkiye

The house fly, Musca domestica (Linnaeus, 1758), is a major threat to public health and food safety due to its ability to transmit numerous pathogenic microorganisms. Despite global control efforts, populations remain abundant in residential areas, livestock facilities, and slaughterhouses, largely due to their high reproductive potential and widespread insecticide resistance. Continuous monitoring of resistance and its underlying mechanisms is therefore essential. In this study, toxicity bioassays were conducted on five strains collected from slaughterhouses using the feeding method. While permethrin, deltamethrin, and bendiocarb were ineffective, thiamethoxam showed variable susceptibility, and fipronil exhibited the highest efficacy. In addition, target-site mutations associated with resistance were screened in a total of 35 samples collected from slaughterhouses and residential areas. A high prevalence of T929I and L1014F mutations in the voltage-gated sodium channel (VGSC) and V260L, A316S, G342A/V, and F407Y mutations in acetylcholinesterase (AChE) - the target sites of pyrethroids and carbamates, respectively - was detected. In silico docking of bendiocarb on M. domestica AChE was conducted for the first time and largely confirmed the functional impact of ace mutations through reduced binding energies. Notably, the L1014H (VGSC) and G342V (AChE) mutations occurred exclusively in slaughterhouse samples, potentially indicating stronger local selection pressure than in residential areas. In contrast, the A301S mutation in the resistance to dieldrin (rdl) gene, the target site of fipronil, was absent from all samples. A haplotype network analysis of all available cytochrome c oxidase subunit I (COI) sequences from GenBank, combined with those generated in this study, revealed a predominant star-like haplotype with low overall genetic diversity, likely reflecting the species' high dispersal ability. Overall, these findings characterize the current resistance status of Turkish house flies and provide essential phenotypic and molecular data to support improved resistance management strategies.