Antifeedant

Antifeedants are organic compounds produced by plants to repel herbivores through distaste or toxicity. These chemical compounds are typically classified as secondary metabolites in that they are not essential for the metabolism of the plant, but instead confer longevity. Antifeedants exhibit a wide range of activities and chemical structures as biopesticides. Examples include rosin, which inhibits attack on trees, and many alkaloids, which are highly toxic to specific insect species, such as quassinoids (extracts from Quassia trees) against the diamondback moth (Plutela xylostella). Samadera indica also has quassinoids used for insect antifeedant uses.

History
"Plant-derived insecticides (e.g., rotenone, veratridines, pyrethrins, and nicotine) have been used for insect control since antiquity." The active ingredients in these plants have been purified and modified. For example, variations on pyrethrin have spawned a large number of synthetic insecticides called pyrethroids.

Culinary implications
In addition to their role defending the plant, antifeedants often confer taste or odors, enhancing the flavor of certain plants. Examples are provided by cruciferous vegetables including mustard, cabbage, and horseradish, which release pungent oils containing glucosinolates when the plant material is chewed, cut, or otherwise damaged. The odorous components of garlic are thought to have evolved to deter insects.