Plant products have been used to kill or repel pest
s since antiquity. In the Middle Ages, Tansy
was spread on floors to kill flea
s and lice
, rubbed on meat
to keep flies
away, and even eaten to get rid of worms
One of the oldest known sources of natural insecticides is the Pyrethrum Daisy, which was used in Persia at least four centuries ago. Now, commercial crops of Pyrethrum Daisy are grown in many parts of the world, and the active ingredients, pyrethrins, are also produced synthetically.
Another useful insecticide of plant origin is rotenone, sold as derris dust, which is extracted from the roots of tropical legumes in the genera Derris and Lonchocarpus. Derris dust breaks down rapidly in the environment and is not toxic to mammals.