Tang Zhen-hua

STUDIES ON THE KINETICS OF ACETYLCHOLINESTERASE IN THE RESISIANT AND SUSCEPTIBLE STRAINS OF HOUSEFLY (MUSCA DOMESTICA)

Abstract Acetylcholinesterase (AChE) in the susceptible (S) and the resistant (R) strains of housefly (Musca domestica) was investigated using kinetic analysis. The Vmax values of AChE for hydrolyzing acetylthiocholine (ATCh) and butyrylthiocholine (BTCh) were 4578.50 and 1716.08nmol/min/mg* protein in the R strain, and were 1884.75 and 864.72 nmol/min/mg. protein in the Sstrain, respectively. The Vmax ratios of R to S enzyme were 2.43 for ATCh and 1.98 for BTCh. The Km values of AChE for ATCh and BTCh were 0.069 and 0.034 mmol/L in the S strain, and 0.156, 0.059 mmol/L in the R strain, respectively. The Km ratios of R to S enzyme were 2.26 for ATCh and 1.74 for BTCh. The ki ratios of S to R enzyme for three insecticides propoxur, methomyl and paraoxon were 46.04, 4.17 and 2. 86, respectively. In addition, kcat and kcat/Km for measuring turnover and catalytic efficiency of AChE were determined using eserine as titrant. The kcat values of AChE from the R strain for both ATCh and BTCh were higher than those values from the S strain. But the values of kcat/Km were in contrary to the kcat values with R enzyme compared to S enzyme. The AChE catalytic properties and sensitivity to the inhibition by three insecticides in the R and S strains of housefly were discussed based on contribution of Vmax, Km, ki, kcat and kcat/Km. All these data implied that AChE from the R strain might be qualitatively altered. We also observed an intriguing phenomenon that inhibitors could enhance the activity of AChE from the resistant strain. This “flight reaction” of the powerful enzyme might be correlated with the developing resistance of housefly to organophosphate or carbamate insecticides.

INHERITANCE OF RESISTANCE TO CYHALOTHRIN IN THE HOUSEFLY (DIPTERA: MUSCIDAE)

Abstract The genetic inheritance of resistance to cyhalothrin in housefly, Musca domstica (L) was investigated.

MOLECULAR MECHANISMS OF TARGET RESISTANCE IN THE ORGANOPHOSPHATE- AND PYRETHROID-RE-SISTANT HELICOVERPA ARMIGERA (HUBNER)

Abstract  The molecular mechanisms of target resistance, i. e. acetyicholinesterase (AChE) and sodium channel insensitivity, in the organophosphate(0P)‐ and pyrethroid(Py)‐resistant (R) Helicoverpa armigera were investigated. The activity and Vmax of AChE from R strain were 1.09– and 1.23‐fold of the susceptible(S) strain respectively, but the KM value of AChE in R strain was only 0.67‐fold of S stain. The Ki values of AChE from the R strain were 0.44 for DDVP and 0.50 for malathion respectively, as compared with those of the S strain. These data showed that the AChE from R strain might be qualitatively altered. The knockdown resistance (kdr) of the resistant H. armigera was also identified by PCR technique. The fragments of IIS6, linker of 11–111 and a part of IIS5‐IIs6 in the sodium channel were cloned and sequenced, and then compared to amino acid sequences from the R and S strains. and other insect species. There was no difference to be found at amino acid level in the above fragments cloned. It was suggested that the Rdr was not involved in the resistance of R strain.