Rocaglamide, a highly substituted benzofuran, was isolated and identified as the main biologically active component in Aglaia elaeagnoidea (syn. A. roxburghiana) for gram pod borer Helicoverpa armigera (Hu¨bner). Addition of rocaglamide to an artificial diet retarded the growth of neonate larvae in a dose-dependent manner with EC 50 values of 0.76 p.p.m. These values compared favourably with azadirachtin (EC 50 ¼ 0.23 p.p.m.). However, azadirachtin was apparently more potent than rocaglamide in inducing growth inhibition via oral administration to these first stadium larvae. The candidate compound was found to have LD 50 and LD 95 values of 0.40 and 1.02 lg per larva, respectively, in topical application against third instar larvae 96 h post-treatment. However, these values for azadirachtin were 8.16 and 25.8 lg per larva for the same period. This shows that azadirachtin was less effective against third instar H. armigera larvae in inducing acute toxicity via topical treatment in comparison with rocaglamide. However, severe morphological larval deformities were observed in such azadirachtin-treated larvae during the process of ecdysis. The cytotoxic nature of rocaglamide was established by evaluating dietary utilization and the results did not implicate any antifeedant effect but the toxicity-mediated effect due to reduced efficiency of conversion of ingested food. It was obvious that feeding deterrence is not the primary mode of action but a centrally mediated effect, which could be due to the induced cytotoxicity at non-specific cellular levels.

The biological activity of azadirachtin, nimbocinol, azadiradione and salannin isolated from Azadirachta indica A. Juss. (neem) was assessed alone and in combination against the cotton bollworm, Helicoverpa armigera (Hübner) and cluster caterpillar, Spodoptera litura (F) (Lepidoptera: Noctuidae). Nimbocinol exhibited growth inhibitory activity in artificial diet bioassays with 82.4 and 92.2 mg kg -1 concentrations inhibiting growth by 50%, respectively, in the two species. This efficacy was almost comparative to azadiradione (EC 50 = 109.6 and 102.1 mg kg -1 ) and salannin (EC 50 = 72.2 and 70.2 mg kg -1 ). Azadirachtin was the most active neem allelochemical against both insect species. In nutritional analysis, only nimbocinol and azadiradione reduced the efficiency of conversion of ingested food (ECI) in feeding experiments, indicating toxic rather than antifeedant effects. In a combination, when azadirachtin was present in a mixture, it always dominated in its efficacy and EC 50 values did not deviate much from the individual efficacy of azadirachtin (0.23 and 0.21 mg kg -1 , against H. armigera and S. litura larvae, respectively). However, enhanced activity among structurally variable molecules was observed, i.e., when salannin combines with nimbocinol or azadiradione, rather than structurally similar molecules like nimbocinol with azadiradione. The activity among nonazadirachtin limonoids in specific combination as opposed to the structural chemistry having explicitly two different modes of action, like feeding deterrence and chronic toxicity, may be playing a significant role in the multicomponent system.