DROSOPHILA ACETYLCHOLINESTERASE - MECHANISMS OF RESISTANCE TO ORGANOPHOSPHATES

Quantitative and qualitative changes of acetylcholinesterase can affec t the sensitivity of insects to insecticides. First, the amount of ace tylcholinesterase in the central nervous system is important in Drosop hila melanogaster, flies which overexpress the enzyme are more resista nt than wild-type flies. On the contrary, flies which express low leve ls of acetylcholinesterase are more susceptible. An overproduction of acetylcholinesterase outside the central nervous system also protects against organophosphate poisoning, that is, flies producing a soluble acetylcholinesterase, secreted in the haemolymph, are resistant to org anophosphates. Second, resistance can also result from a qualitative m odification of acetylcholinesterase. Four mutations have been identifi ed in resistant strains: Phe115 to Ser, Ileu199 to Val, Gly303 to Ala and Phe368 to Tyr. Each of these mutations led to a different pattern of resistance and combinations between these mutations led to highly r esistant enzymes.