Azadirachtin from the neem tree Azadirachta indica: its action against insects

The neem tree has long been recognized for its unique properties both against insects and in improving human health. It is grown in most tropical and sub-tropical areas of the world for shade, reforestation and for the production of row material for natural insecticides and medicines. Azadirachtin, a complex tetranortriterpenoid limonoid from the neem seeds, is the main component responsible for the toxic effects in insects. Six international conferences on neem and a vast scientific literature report both the antifeedant and physiological effects of neem. This article reviews the behavioral and physiological properties of azadirachtin, including effects on insect reproduction, direct and "secondary" antifeedancy, and the physiological effects measured as growth reduction, increased mortality and abnormal and delayed moults. These effects are here categorized in two ways: direct effects on cells and tissues and indirect effects exerted via the endocrine system. It also describes the work carried out to date to identify the mode of action of azadirachtin at the cellular level. The differential effects between animal phyla and over non-target organisms are discussed and point to its potential success as a safe insecticide.