Fresh rhizomes of Zingiber officinale (ginger), when subjected to steam distillation, yielded ginger oil in which curcumene was found to be the major constituent. The thermally labile zingiberene-rich fraction was obtained from its diethyl ether extract. Column chromatography of ginger oleoresin furnished a fraction from which [6]-gingerol was obtained by preparative TLC. Naturally occurring [6]-dehydroshogaol was synthesised following condensation of dehydrozingerone with hexanal, whereas zingerone and 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)butane were obtained by hydrogenation of dehydrozingerone with 10% Pd/C. The structures of the compounds were established by 1H NMR, 13C NMR and mass (EI-MS and ES-MS) spectral analysis. The test compounds exhibited moderate insect growth regulatory (IGR) and antifeedant activity against Spilosoma obliqua, and significant antifungal activity against Rhizoctonia solani. Among the various compounds, [6]-dehydroshogaol exhibited maximum IGR activity (EC50 3.55 mg ml-1), while dehydrozingerone imparted maximum antifungal activity (EC50 86.49 mg litre-1).

Photostability of azadirachtin-A (a neem based pesticide) has been studied without and with adding stabilizers such as ter. butyl-p-cresol, 8-hydroxy quinoline and ter. butyl hydroquinone as thin film on glass surface and on leaf surface under sunlight and UV light. Half-life of azadirachtin has been found to be 48 min and 3.98 days as thin film under UV light and sunlight and 2.47 days on leaf surface, respectively. 8-Hydroxy quinoline and ter. butyl hydroquinone have been found effective in controlling degradation of azadirachtin under both sunlight and UV light with half-life of 44.42 and 35.90 days under sunlight, and 55.80 and 48.50 h under UV light, respectively. Whereas ter. butyl-p-cresol has been found effective A only under sunlight. Significant decreases in antifeedant and insect growth regulatory activity against third instar larvae of Spodopterra litura has been observed with azadirachtin when exposed to sunlight and UV light. However, by the addition of above stabilizers, the biological activity of azadirachtin-A has been retained even after 24 h of irradiation under UV light and up to 30 days of exposure to sunlight.

Antifeeding and insect growth regulatory effects of saponins and its hydrolyzed products from Diploknema butyracea and Sapindus mukorossi on the insect pest Spodoptera litura (F.) were investigated in the laboratory. D. butyracea saponins as well as their hydrolyzed prosapogenins were found to be better biologically active in controlling pests. A concentration of 1200 and 3400 mg L(-1) alkaline and acid hydrolyzed D. butyracea saponins exhibited significant antifeeding and toxic effects to third instar larvae when compared to the emulsified water as control. The n-BuOH extract after prep-HPLC separation provided two saponins from the D. butyracea saponin mixture: 3-O-[beta-D-glucopyarnosyl-beta-d-glucopyranosyl]-16-alpha-hydroxyprotobassic acid-28-O-[ara-glc-xyl]-ara (MI-I) and 3-O-beta-D-glucopyranosyl-glucopyranosyl-glucopyranosyl-16-alpha-hydroxyprotobassic acid-28-O-[ara-xyl-ara]-apiose (MI-III). The single saponin extracted from the S. mukorossi saponin mixture was 3-O-[beta-D-xyl(OAc).beta-D-arabinopyranosyl.beta-D-rhamnopyranosyl] hederagenin-28-O-[beta-D-glc.beta-D-glc.beta-D-rhamnopyranosyl] ester (SM-I). Five days after saponin treatment on larvae, the growth index (GI50) was reduced from 0.92% to 1520 ppm in alkaline hydrolyzed D. butyracea saponins. Upon hydrolysis, growth regulatory activity was improved in S. mukorossi saponin, whereas very little difference was found in antifeedant activity. Hydrophile-lipophile balance is important for the proper functioning of saponin/prosapogenin/sapogenin, which could be achieved by manipulating the sugar molecule in the triterpenic skeleton.

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A 60% azadirachtin-A concentrate has been obtained through repeated precipitation with hexane from a methanolic solution of a 20% concentrate. Azadirachtin-A (90%) has been obtained by medium-pressure liquid chromatography of the 60% concentrate with an RP-18 column and a methanol + water (1 + 1 by volume) solvent system. Catalytic hydrogenation of the 60 and 90% azadirachtin concentrates yielded the corresponding tetrahydroazadirachtin concentrates. Dihydroazadirachtin and tetrahydroazadirachtin formed during the first 5 h of hydrogenation were identified by LC-ESI-MS on the basis of their unique mass fragmentation pattern. The efficacy of tetrahydroazadirachtin concentrates in inhibiting the feeding and growth of Helicoverpa armigera (Hübner) larvae has been compared with that of azadirachtin concentrates. They were in general more active and deterred larvae from feeding at all concentrations. Tetrahydroazadirachtin-A (90%) and azadirachtin-A (90%) with respective IC(50) values of 280 and 390 mg L(-1) were effective as insect growth regulators, while tetrahydroazadirachtin-A (90%) displayed higher antifeedant activity (AI(50) 14 mg L(-1)) against the test insect.

Three consecutive sprays of THA, a neem-based biopesticide, and endosulfan have been found to be superior in controlling field pests of okra to Aza-A and NZ, which were on a par. THA thus holds potential as a component of pest management strategies against okra pests.

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