Resistance Mechanisms To Organophosphorus And Carbamate Insecticides In Housefly, Musca Domestica L.

Dichlorovos resistant housefly (Musca domestica L.) was obtained by selection using DDVP in laboratory. Acetylcholinesterase (AChE) and carboxylesterase (CarE) from resistant and susceptible housefly strain were investigated on the biochemical and toxicological properties.The resistant housefly strain was selected with DDVP totally for 42 generations. The resistance ratios changed little from F0 to F13.but began to increase from F14, especially after F22. The resistance ratio of the F42 generation was 18.06 folds in comparison with the susceptible strain. Resistance selection to DDVP had no effect on AChE activity, but CarE activity of DDVP-resistance housefly was higher than that of the susceptible strain. LD50 of resistance housefly to deltamethrin was 1.24 folds in comparison with the susceptible strain. It seemed that the DDVP-selected strain had no cross-resistance to deltamethrin.The studies revealed that optimal reaction condition of AChE: concentration of enzyme was 2.5 head/ml, optimal temperature was 30 C and optimal time was 15 minute. Optimal concentration of enzyme for CarE specific activity detection was 5 head/ml, and the optimal temperature and reaction time were same as those of AChE.The Michaelis constant (Km) of resistant housefly was 2.35 folds higher than that of susceptible strain, which showed there was qualitative change in AChE from resistant housefly and the affinity of AChE to ATCh reduced compared with that of the susceptible" strain. Bimolecular rate constants (Ki) to DDVP, eserine, omethoate, methomyl and propoxur of resistant housefly were lower than that of the susceptible strain, which were 26.51, 7.80, 7.70,12.54 and 22.48 times, respectively, in comparison with the susceptible strain, indicating the enzyme was insensitive to these insecticides. AChE is the target site for organophosthate and carbamate insecticides, the sensitivity reduction of AChE to the inhibition of these insecticides was the main reason that housefly had become resistant to organophosthate and carbamate insecticides.The residual activity of AChE under the different concentration of DDVP and propoxur reduced faster than that of eserine. Residual activity of AChE of resistant strain was higher than that of susceptible housefly.The residual activity of AChE inhibited by DDVP and eserine for different time reduced slower than that of propoxur. Activity of AChE was inhibited evidently by propoxur in the first 5 minutes.