Isolation and structural studies on a locust feeding inhibitor from neem seeds

Abstract

Two species of Meliaceae, neem (Azadirachta indica A.Juss) and Melia azedarach L. have been reported by various workers to inhibit feeding in the desert locust (Schistocerca gregaria). In this work a systematic investigation of extracts of neem seeds has been carried out in order to isolate a locust feeding inhibitor. Antifeeding activity was measured by presenting fifth instar hoppers of the desert locust with filter papers which had been impregnated with a solution of the extract to be tested and allowed to dry and then sprayed with 0.25 M. sucrose solution and allowed to dry again.
In this way a locust feeding inhibitor, azadirachtin, has been isolated. This compound completely inhibits feeding with test solutions down to a concentration of 40 µg./1.
Azadirachtin, molecular formula C35H44O16, is a colourless non-crystalline compound which is probably related to the limonoids and triterpenoids already isolated from Meliaceae, but is more highly oxygenated. It has so far been shown to contain two hydroxyl groups, two acetoxy groups, one tiglate ester group, two methyl ester groups and a dihydrofuran ring.