Chemical Constituents of Colocasia esculenta leaves extract in Relation to its Self Defense against the Cotton leafworm, Spodoptera littoralis (Boisd.)

Plants evolved elegant and complex chemical systems to defend themselves against the pathogens and herbivores that attempt to consume them. Taro, Colocasia esculenta plant has self defense property; it may be containing natural organic substances, allelochemicals, which are biologically active. The anti-feeding and insecticidal activities of petroleum ether extract of Colocasia esculenta leaves were studied against the 4th instar larvae of Spodoptera littoralis under laboratory conditions. Anti-feeding activity was assessed based on anti-feeding indices under choice and no-choice conditions. The highest anti-feeding activity is reached under no-choice conditions and anti-feeding indices were concentrations dependent; also it was found that the extract exhibits larval toxicity, the toxicity of the extract increased with time post treatment. Petroleum ether extract of Colocasia esculenta leaves was subjected to saponification reaction; from the un-saponifiable matter of petroleum ether extract, two phytosterols; namely β-sitosterol and stigmasterol were isolated by column chromatography (CC) and thin layer chromatography (TLC). Their structures were elucidated by 1H-NMR and MS techniques. The presence of these two compounds in C. esculenta leaves may be one reason of its self defense. This is the first record on the isolation and identification of chemical constituents from Colocasia esculenta leaves.