New triterpenoid saponins from Clematis lasiandra and their mode of action against pea aphids Acyrthosiphon pisum

Abstract

Natural products are important sources for the discovery of new biopesticides to control the worldwide destructive pests Acyrthosiphon pisum Harris. Three new triterpenoid saponins, neolasiandrosides A–C (1–3), along with seven known ones (4–10), were identified from Clematis lasiandra by extensive spectra and chemical evidences. Neolasiandrosides A and B (1 and 2) with the dammarane-type tetracyclic aglycone were identified for the first time from Clematis. Neolasiandroside C (3) was a bidesmoside, characterized at the aglycosylation sites at C-23 and C-28 in the hederagenin aglycone. Compounds 1–10 exhibited significant aphicidal activities against A. pisum through oral toxicity (LC50 = 0.13–0.98 mg/mL, 72 h) and deterrent effect with deterrence index (DI) of 0.33–0.90 at 0.125 mg/mL after 24 h, while showed no contact toxicity. Compounds 1 and 6 showed potent inhibitory effects on digestive enzymes of pepsin and α-amylase with the inhibition rate of 84.0 % and 85.7 %, 55.3 %, and 51.5 %, respectively, at the dose of LC80, while appeared inactive to acetyl cholinesterase (AChE) and chitinase in A. pisum. The toxic symptoms of A. pisum caused by 6 involved body-color changes from light green to dark green, and brown until death. Transmission electron microscope (TEM) analysis demonstrated that the organelles including apical microvilli, nuclei, and mitochondria in the midgut tissues were the targeting sites for 6 exerting its aphicidal activity. The results provided new light for the industrial application of triterpenoid saponins from Clematis as novel biopesticides.