Monitoring of Thiamethoxam Resistance in Turkish House Fly Strains, Musca domestica (Diptera: Muscidae)

Background: The house fly, Musca domestica, is vector for pathogens and parasites and causes economic damage to livestock by reducing forage conversion efficiency, negatively impacting weight gain and milk production. It has shown resistance to multiple insecticide classes. The aim of this research was to determine the susceptibility levels of seventeen field M. domestica strains to thiamethoxam, a neonicotinoid insecticide, in Türkiye. Methods: Insecticide susceptibility of the house flies to thiamethoxam was determined using the WHO glass jar method. A probit analysis program was used to determine LD50 values, and then the resistance ratios were compared with insecticide-susceptible strain. Results: All strains were ≥18.5-fold resistant to thiamethoxam. The data showed that 10 out of 17 strains had either high or very high resistance levels. Our findings revealed that house flies from solid waste landfills in Samsun, Ankara, and Kocaeli exhibited higher resistance ratios compared to those found in animal shelters. Conversely, in Gaziantep, Antalya, İzmir and Erzurum, the exact opposite trend was observed. Regarding the LD50 values among solid waste storage areas, the lowest rate was obtained from Gaziantep (0.72 gr ai/m²), and the highest rate was obtained from Ankara (9.35 gr ai/m²). Furthermore, regarding the LD50 values among animal shelters, the lowest was obtained from Samsun (0.37 gr ai/m²), and the highest was obtained from Denizli (21800 gr ai/m²). Conclusion: The use of integrated control systems is recommended for controlling house fly populations, including insecticide class rotations for preventing, or at least, delaying the onset of resistance.