Understanding the changes in insect organisms due to insecticide exposure and their species-specific responses is crucial for comprehending the evolutionary and environmental aspects of pesticide resistance. While the mechanism behind resistance to chlorfenapyr, a pyrrole group insecticide, remains unclear, this study investigates the acetylcholinesterase (AChE) activity in adult houseflies (Musca domestica) of a chlorfenapyr-resistant strain (ChlA) selected with chlorfenapyr. This research also compares the kinetic parameters of AChE in female and male ChlA strains to those in an unselected strain (Lab) of M. domestica for the first time. No significant differences were observed in the specific AChE activity between the ChlA and Lab strains. However, the remaining activity of propoxur-inhibited AChE in ChlA females was significantly lower (3.81 times less, P < 0.05), and the Vmax and Km values were reduced by 43.3% and 46.9% (P < 0.05), respectively, when compared to Lab females. Furthermore, the catalytic efficiency of AChE expressed as Vmax/Km, was higher in males than females in both strains. Overall, the results indicate that in ChlA females, the affinity of AChE for specific ligands, such as acetylthiocholine (substrate) and propoxur (inhibitor), increased without a corresponding increase in catalytic activity, which may be attributed to the selection of chlorfenapyr during 23-24 generations.
