Studies on the acetylcholinesterase of Anopheles albimanus resistant and susceptible to organophosphate and carbamate insecticides

Acetylcholinesterase from fourth instar Anopheles albimanus larvae was studied in vitro. The acetylcholinesterase from both the resistant and susceptible strains behaved as a single enzyme "type," with straight pseudo first-order insecticide inhibition lines which intersected the Y axis at 100%. The enzyme from resistant larvae was more slowly inhibited than the susceptible enzyme; bimolecular rate constants (ki) differed by approximately 1.2- to 6-fold for a range of organophosphorous compounds and 17- to 1570-fold for the carbamates. There was a good correlation between the levels of resistance and the acetylcholinesterase inhibition rates.