Insecticidal Constituents of Azadirachta indica and Melia azedarach (Meliaceae)

The insecticidal constituents of the Indian neem tree ( Azadirachta indica ) and the related chinaberry tree ( Melia azedarach ) were investigated using bioassay-guided fractionation and isolation techniques. Azadirachtin was isolated as the principal insecticidal and antifeedant constituent of A. indica seeds. In addition, 25 volatile compounds were identified as constituents of crushed neem seeds. The major volatile constituent identified, di-n-propyl disulfide, was shown to be larvicidal to three species of insects. Furthermore, two new insecticidal compounds, 1-cinnamoylmelianolone and 1-cinnamoyl-3,11-dihydroxymeliacarpin, were isolated from the fruit of M. azedarach . The insecticidal activities of these new compounds, compared with those of azadirachtin and several of its derivatives, suggest structure-activity relationships and a mode of action that may be useful in the design of synthetic analogs.