The Biological Role of Toxic Secondary Metabolites of Different Origins on Insect and Humans

Plant toxins are photochemical or secondary metabolites formed naturally by plants. They protect themselves against various threats like bacteria, Fungi, nematodes, insects, etc. Among secondary plant metabolites, one can find alkaloids, terpenoids, steroids, glycosides, phenolics, tannins, and others. Humans have used these secondary metabolites over thousands of years, both as drugs and agents to kill animals and humans. Some insects are food specialists and can feed on normally toxic plants to other herbivores. Many plant secondary metabolites interfere with the neuro receptors and neurotransmitters in vertebrates. Insects share many neuro receptors with vertebrates. PSM serves as olfactory cues for insects to identify their appropriate food plants. The behavior of insects towards such chemicals cues reminds us of drug addiction in humans and other vertebrates. This Chapter is incorporated the major aspects of plants’ secondary metabolites and their impact on insect ecological adaptation.