For centuries, India’s farmers have known that the Neem trees withstand the periodic infestations of locusts.
Neem extracts applied to vegetable crops repel locusts (Heinrich Schmutterer, 1962). Like most plants, neem deploys internal chemical defences to protect itself against leaf- chewing insects. Its chemical weapons are extraordinary, however.
Neem contains several active ingredients, and they act in different ways under different circumstances. These compounds bear no resemblance to the chemicals in today’s synthetic insecticides. Chemically, they are distant relatives of steroidal compounds, which include cortisone, birth-control pills, and many valuable pharmaceuticals. Composed only of carbon, hydrogen, and oxygen, they have no atoms of chlorine, phosphorus, sulfur, or nitrogen (such as are commonly found in synthetic pesticides). Their mode of action is thus also quite different.
Neem products are unique in that (at least for most insects) they are not outright killers. Instead, they alter an insect’s behavior or life processes in ways that can be extremely subtle. Eventually, however, the insect can no longer feed or breed or metamorphose, and can cause no further damage.