Selected Plant Essential and Seed Oils and their Secondary Metabolites Used as Insecticides: A Review

Abstract

Conscious consumers around the world have been getting organized to urge and encourage farmers to practice environmentally and human friendly organic agricultural production. Synthetic insecticides have been established to be toxic to the environment, non-target organisms and even to humans when used to control problematic insects in the homes/gardens and in agricultural establishments. On the other hand, plant-based insecticides have proven to be environmentally friendly and less toxic to non-target organisms and less detrimental to human health due to their short half-lives. This is because they do not possess ‘unnatural’ ring structures with relatively few halogen substituents, known to be closely related with disease states and genetic abnormalities, including cancer. Plant based oils such as cinnamon, garlic, peppermint, rosemary essential oils and castor, neem, sesame seed oils have been found to contain secondary metabolites with effective insecticidal activities. These secondary metabolites include cinnamaldehyde, which has been found to kill common house flies; ricin, which has been found to effectively control diamondback moth; dimethyl trisulphide and diallyl disulphide, which have been found to effectively kill red flour beetle; azadirachtin and menthol, which have strong insecticidal activity against malaria causing and dengue fever mosquitoes; α-Pinene, which has been found to have repellence effects on aedes mosquitoes; sesamin, with strong insecticidal activity against agricultural fungus-growing termites; and thymol, with strong larvicidal activities against malaria causing mosquitoes