Abstract: The method of making a neurotoxic insecticide which comprises:1. Extracting a relatively heat stable, lipophilic, calcium linked, free sufhydryl, proteinaceous extract from casein, in particular the kappa casein thereof, or a casein containing material, such as skim milk, with a low molecular weight alcohol or acetone, and recovering the extract;2. Mixing the extract with one or more membrane transfer agents, such as detergents or solvents, which allow the transfer of the protein extract across normally impermeable insect membranes, whereby the extract demonstrates neurotoxic insecticidal effects.