More than a hundred terpenoids are known from different parts of the Neem plant. Of its biological constituents, the most active and well studied compound is Azadirachtin. However in most traditional preparations of Neem as pesticide or medicine, a mixture of Neem chemicals are present and provide the active principles. The Neem terpenoids are present in almost all parts of the plant, in the living tissues. Recently, the site of synthesis and accumulation of Neem chemicals has been identified as secretory cells.
Secretory cells are most abundant in the seed kernels.
For Protecting Crops Neem is quite effective against army worm, one of the most devastating pests of food crops in the western hemisphere. Neem extract is useful against leaf - miner, a serious pest in parts of North America. Neem seed extract works as well as available commercial synthetic pesticides. It has been approved by the US environmental protection agency for use on Leaf Miners. Experiments have shown that neem is also effective against fruit flies.