Identification of azukisapogenol triterpenoid saponins from Oxytropis hirta Bunge and their aphicidal activities against pea aphid Acyrthosiphon pisum Harris

Abstract

Background: Acyrthosiphon pisum Harris is the most destructive pest worldwide because of its ability to feed on plants directly and transmit plant viruses as a vector. This study aims to identify triterpenoid saponins from Oxytropis hirta Bunge as biopesticides to control aphids.Results: Three new azukisapogenol triterpenoid saponins (1-3), a new pinoresinol lignan glycoside (8), and four known saponins (4-7) were identified from the root of O. hirta. Compounds 4-7 displayed significant aphicidal activities against A. pisum with oral toxicities (LC 50 = 51.10-147.43 ∼g/mL, 72 h), deterrent effects (deterrence index = 1.00, 100-200 ∼g/mL, 24 h), and aphid reproduction inhibitory effects (inhibition rates = 75.91-86.73%, 400 ∼g/mL, 24 h), respectively. The carboxyl groups at C-3 GlcA and C-30 were functional groups for their aphicidal activities. The toxic symptoms caused by the optimal 5 involved insect body-color changes from light green to dark or gray-green, and then brown until death. The intestinal cavity, apical microvilli, nuclei, mitochondria, and electron dense granules in the midgut tissues of A. pisum were the target sites showing aphicidal activity. The suppression of pepsin and ⊍-amylase, and the activation of lipase and trypsin could be the signs of organelle damage in the midgut tissues.Conclusion: Azukisapogenol triterpenoid saponins from O. hirta could be used as biopesticides to control aphids for their multiple efficacies, including oral toxicity, deterrent activity, and reproduction inhibitory activity. The toxic symptoms involved insect body-color changes. Midgut tissues and their related enzymes were the targets for saponins showing aphicidal activities.

Discovery of New Botanical Insecticides: Identification and Insecticidal Activity of Saponins from Clematis obscura Maxim and Insights into the Stress Response of Acyrthosiphon pisum Harris

“…Previous studies demonstrated that triterpenoid saponins displayed their aphicidal activities against A. pisum through oral toxicities and antifeedant effects, while not dependent on contact toxicities. , Herein, almost all the identified saponins exhibited antifeedant activities and oral toxicities against A. pisum at 400 μg/mL.…”

“…We speculated that saponin 8 might be located at midgut epithelial first, and then broke it, just like related reports of periplocoside NW against Mythimna separate Walker larvae and saponins against A. pisum. 22,23,41 Meanwhile, it was reported that the cuticular lining of the foregut and hindgut also contained chitins. 39 Therefore, the destruction of the intestinal structure may also be related to the disorder of the chitin metabolism.…”

“…A diet incorporation method with little modification was used to assess the antifeedant activity and oral toxicity of compounds 1−14 against A. pisum. 22,23 The details are described in Text S4. The antifeedant activity was assessed by the deterrence index (DI), which was counted as DI = (C − T)/(C + T), where C and T are the numbers of A. pisum on the blank control half 50 , 100 μg/mL, 72 h) were chosen to observe the epidermis by the SEM method according to the following steps.…”

“…16 Triterpenoid saponins isolated from Clematis lasiandra and Oxytropis hirta Bunge presented potential aphicidal and deterrent effects against A. pisum. 22,23 attention. Herein, the key insecticidal constituents of 14 triterpenoid saponins (1−14) were isolated from the n-BuOH extracts of C. obscura (Figure 1).…”

Antifeedant and insecticidal effects of alfalfa saponins in the management of the Japanese beetle Popillia japonica

“…Among various tested saponins, 3‐GlcA‐28‐AraRhaXyl‐medicagenic acid (compound 14 , Figure 2), the most abundant compound in our saponin mixture is reported to be potentially responsible for insecticidal activity (Singh & Kaur, 2018). However, as suggested by Li et al (2022), Tian et al (2021) and Ye et al (2023), also some other minor constituents with particular functional groups could act as pesticides, but further research is needed to solve this topic. To the best of our knowledge, the employment of M. sativa saponins in the control of the P. japonica pest has not been investigated so far, while few works against other Coleoptera have been reported.…”