Antifeedant bioactivity of sesquiterpene lactones from neurolaena lobata and their antagonism by γ-aminobutyric acid

The germacranolides and furanoheliangolides isolated from aerial parts of Neurolaena lobata (L.) R.Br. are assessed as antifeedants against fifth instar larvae of Spodoptera litura (Noctuidae) using leaf disc bioassays. In terms of potency, they are less active than parthenolide, more active than picrotoxinin, and comparable to strychnine. The antifeedant effect of neurolenin B, appears to result from interaction with GABA A receptors in the chemosensilla of S. litura as suggested for the known GABA antagonists strychnine and picrotoxinin. All three compounds show strong antifeedant activities, which are completely lost after simultaneous co-administration of equimolar GABA.