Isolation, characterization and mode of action of a larvicidal compound, 22-hydroxyhopane from Adiantum latifolium Lam. against Oryctes rhinoceros Linn.

Oryctes rhinoceros Linn. is one of the most serious pests of coconuts and other palms. Following bioassay guided method, a larvicidal compound, 22-hydroxyhopane has been isolated for the first time from methanol extract of leaves of Adiantum latifolium Lam. against the pest (LC₅₀ value 20.81 μg/g). It is a hopanoid triterpene with molecular mass of 442.42 g/mol. The compound exhibited antibacterial activity against symbiotic gut bacteria, caused histolysis of midgut tissues and inhibited secretion of digestive enzymes such as protease, amylase and trehalase resulting in weight loss of larvae. Enzyme immunoassay showed an elevation of 20-hydroxyecdysone level in haemolymph causing disruption of metamorphosis of larvae.