Discovery of New Botanical Insecticides: Identification and Insecticidal Activity of Saponins from Maxim and Insights into the Stress Response of Harris.

To discover new botanical products-based insecticide candidates, 14 triterpenoid saponins (-) including four new ones, obscurosides A-D (-), were isolated from Maxim as potential agrochemicals against Harris and (L.). Compounds - were characterized by a rare ribose substitution at C-3, and was a bidesmoside glycosylated at the rare C-23 and C-28 positions of the oleanane aglycone. Compounds (median antifeeding concentration, AFC = 1.10 mg/mL; half-lethal concentration, LC = 1.21 mg/mL) and (AFC = 1.09 mg/mL, LC = 1.37 mg/mL) showed significant insecticidal activities against third larvae of at 72 h. All saponins displayed antifeedant activities against with the deterrence index of 0.20-1.00 at 400 μg/mL. Compound showed optimal oral toxicity (LC = 50.09 μg/mL) against , followed by compounds , -, , and (LC = 90.21-179.25 μg/mL) at 72 h. The shrinkage of the cuticle and the destruction of intestinal structures of microvilli, nucleus, endoplasmic reticulum, and mitochondria were toxic symptoms of -treated . The significantly declined Chitinase activity in -treated with an inhibition rate of 79.1% at LC (70% lethal concentration) could be the main reason for its significant oral toxicities. Molecular docking revealed favorable affinities of compounds and with group I Chitinase ChtI (Group I Chitinase from ) through conventional hydrogen bonds and alkey/π-alkey interactions by different patterns. These results will provide valuable information for the development of novel botanical pesticides for the management of insect pests, especially against .