Abstract
The property of nonspecific esterases and acetylcholinesterases was studied in organophosphate (OP)-susceptible (SRS), OP-resistant (Akita and Yume) and OP-selected (Akita-f and Yume-m) strains of the housefly, Musca domestica L. Housefly head esterases were separated into six molecular species (I-VI) by polyacrylamide gel electrophoresis and their activity was assayed using indoxyl acetate and acetylthiocholine as substrate. Esterases II and VI, which were classified as nonspecific esterases, clearly increased their indoxyl acetate activity with development of resistance. The other esterases did not change their activity. Esterases I, III and IV, which were identified as acetylcholinesterases, decreased their sensitivity to OP inhibition with development of resistance. The OP sensitivity of nonspecific esterases was little changed.
