Termite antifeedant activity in Xylopia aethiopica

Abstract

A hexane extract of Xylopia aethiopica fruits and an aqueous methanol extract of the seeds were studied for termite antifeedant activity against workers of the subterranean termite, Reticulitermes speratus. The crude extract, at 1%, exhibited strong antifeedant activity in a choice filter paper disk bioassay. Bioassay-directed fractionation led to the isolation and identification of six ent-kaurane diterpenes in the hexane extract. Feeding deterrent activity varied significantly with the structures when the compounds were tested at concentrations ranging from 5000 ppm (40 μg cm −2) to 100 ppm (0.824 μg cm −2). (−)-Kaur-16-en-19-oic acid had the strongest termite antifeedants activity among the ent-kauranes isolated. Two phenolic amides and four lignanamides were also isolated from the aqueous methanolic extract of seeds. E-3-(4-hydroxy-3-methoxyphenyl)- N-2-[4-Hydroxyphenylethyl]2-Propenamide was more active than E-3-(3,4-dihydroxyphenyl)- N-2-[4-Hydroxyphenylethyl]2-propenamide, whilst grossamide and the new lignanamide, demethylgrossamide, as well as (−)-cannabisins B and D exhibited potent feeding deterrent activity at 5000 ppm. The identity of these compounds was established by spectroscopic analysis and synthesis. Two synthetic amides, E-3-(3,4-methylenedioxyphenyl)- N-2-[4-Hydroxyphenylethyl] propenamide and E-3-(3,4-methylenedioxyphenyl)- N-2-[octadecyl]-2-propenamide were also tested for antifeedant activity.