Here we present a multi-session, investigative lab sequence that examines the effectiveness and biochemistry of plant essential oils as ?natural? insecticides against the bean beetle Callosobruchus maculatus. Due to concerns about the effects of chemical insecticides on human health and non-target organisms as well as increasing levels of insecticide resistance observed in the field, there is interest in using ?natural? insecticides to replace chemical insecticides. There is evidence that several plant essential oils are toxic to different insect pests and that their toxicity may be due to inhibition of various enzymes. Bean beetles are pests of legume seeds, and are easy to culture and use in a teaching laboratory. Students can use fumigant toxicity assays to determine effectiveness of commercially available essential oils from closely or distantly related plant species as natural insecticides against bean beetles. The students can study potential unintended consequences of using such ?natural? insecticides by studying their effects on enzymes extracted from other organisms such as fish and mammals. Students can also study the effect of plant essential oils on several enzymes extracted from bean beetles as potential targets of the ?natural? insecticide. This lab sequence relates enzyme activity to evolutionary processes in plant-animal interactions, ethnobotany, and agroecology.
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