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 <i>Rhododendron capitatum</i>. Insecticidal activity assays against four aphid species revealed that compound <b>33</b> exhibited potent oral toxicity, with LC₅₀ values of 95.9-387.6 μg/mL, outperforming tea saponin (LC₅₀: 258.6-1653.0 μg/mL) and approaching half the efficacy of rotenone against <i>Aphis citricola</i> (LC₅₀ = 160.3 μg/mL). Additionally, compounds <b>29</b> and <b>33</b> showed strong repellent effects against <i>Acyrthosiphon pisum</i> (RI = 1.00 at 800 μg/mL, 24 h). Morphological alterations in aphids, and enzymatic inhibition assays, indicated that <b>33</b> 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 <i>R. capitatum</i>, particularly capitatoside J (<b>33</b>), as promising natural leads for aphid control.