Piperine analogs in a hydrophobic fraction from Piper ribersoides (Piperaceae) and its insect antifeedant activity

Piper ribersoides Wall. (Piperaceae), which is called “Khua Sa khan” in the local language, is mainly grown in Laos. This plant is used as a food in Laos, but no report on its metabolites exists. Crushed stems were immersed in methanol. The ethyl acetate fraction showed potential insect antifeedant activity for Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), and some of the active compounds were piperine analogs. Piperine and its geometrical isomer independently showed potent antifeedant activities, and piperine was presumably the main active compound in the methanol extract. Interestingly, we discovered that the antifeedant activity was reduced when they were mixed (50:50).