Evaluation of Insecticidal Application Potential of Glycoside Derivatives from Rhododendron capitatum against Four Aphid Species

To discover novel botanical insecticides against aphids, 46 phenolic compounds including 13 previously unreported ones (capitatosides A–M), were obtained from the aerial parts of Rhododendron capitatum . Insecticidal activity assays against four aphid species revealed that compound 33 exhibited potent oral toxicity, with LC 50 values of 95.9–387.6 μg/mL, outperforming tea saponin (LC 50: 258.6–1653.0 μg/mL) and approaching half the efficacy of rotenone against Aphis citricola (LC 50 = 160.3 μg/mL). Additionally, compounds 29 and 33 showed strong repellent effects against Acyrthosiphon pisum (RI = 1.00 at 800 μg/mL, 24 h). Morphological alterations in aphids, and enzymatic inhibition assays, indicated that 33 likely exerts its insecticidal activity against four agriculturally significant aphid species through suppression of Chitinase and α-amylase. Furthermore, the SAR analysis was also discussed in the article. These findings highlight the glycoside derivatives of R. capitatum, particularly capitatoside J ( 33 ), as promising natural leads for aphid control.