Evaluation of Insecticidal Application Potential of Glycoside Derivatives from <i>Rhododendron capitatum</i> 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.