Microassay of acetylcholinesterase activity in small portions of single mosquito homogenates.

1. A simple, rapid microassay method is described for measuring acetylcholinesterase (AChE) activity accurately and precisely in small portions of single mosquito homogenates. 2. Up to 30 microassay replicates were possible for individual insects. 3. Microassay data on individual mosquitoes were compared with conventional enzyme assay data acquired using pools of the same homogenates. 4. Under the optimum reaction conditions established, an average Vmax of 7.1 nmol/l/min/mosquito and an average Km of 1.3 x 10(-4) M were observed with acetylthiocholine iodide as substrate. 5. Variability in AChE activity within a sample population of Anopheles albimanus was observed using measurements from individual insects. 6. Such information is fundamental to comparative studies of pesticide physiology (in particular, the resistance phenomenon) in the individual mosquitoes in a population pool; this technique forms the basis for a recently developed resistance microassay.