Here we describe an enzyme assay to look at the effect of the organophosphate insecticide malaoxon on the activity of acetylcholinesterase (AChE) in the bean beetle Callosobruchus maculatus. Malaoxon inhibits the activity of AChE and interferes with neuronal activity. The procedure involves a crude protein extraction and a colorimetric assay to determine enzyme activity. The procedure is also used to investigate whether the inhibition by the insecticide is competitive or non-competitive. These lab exercises tie in several topics together: data processing and presentation, enzymatic reactions and enzyme inhibitors, cell-cell signaling, and biological applications to industry and their potential ecological consequences.