The antifeedant, insecticidal and insect growth inhibitory activities of triterpenoid saponins from Clematis aethusifolia Turcz against Plutella xylostella (L.).

Abstract

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a global insect pest of crops, leading to a reduction of agricultural products in productivity and quality. Plant saponins are rich sources for the discovery of candidates to control insect pests. This study focused on discovery of triterpenoid saponins from Clematis aethusifolia Turcz and evaluation of their antifeedant, insecticidal and insect growth inhibitory activities against the 3rd instar larvae of P. xylostella. Seven triterpenoid saponins (1-7) were isolated for the first time from the n-BuOH extract of C. aethusifolia. Monodesmosides 1, 2, and 5 with a free 28-COOH group showed much higher antifeedant activity (DC50 were 733.67-844.77 μg mL-1 at 24 h, and 737.19-748.28 μg mL-1 at 48 h) than bidesmosides 3-4 and 6-7 (DC50 were 1284.35-2053.98 μg mL-1 at 24 h, and 1183.72-1990.96 μg mL-1 at 48 h). Similarly, monodesmosides 1, 2, and 5 (LC50 were 1462.78-1785.96 μg mL-1 ) showed stronger insecticidal activity than bidesmosides 3-4 and 6-7 (LC50 were 2219.22-3050.51 μg mL-1 ) against P. xylostella at 72 h. These results suggest the 28-COOH group is an important functional group for their antifeedant and insecticidal activity. Besides, monodesmosides 1, 2, and 5 showed insect growth inhibitory activity against P. xylostella through reduction of larval growth and percentage of pupation, associated with prolongation of larval and pupal stages. The present results provide evidence that triterpenoid saponins from C. aethusifolia, particularly those monodesmosidic saponins with a free 28-COOH group, have the potential to be developed as pesticides to control P. xylostella.