Synergistic boosting of insecticide efficacy by the phytochemical (−)-(S)-palasonin: A cross-class enhancement for aphid control with laboratory-field concordance

Aphids impose chronic yield and quality losses in intensive production systems while escalating resistance erodes the reliability of conventional insecticides. Plant-derived actives from industrial crops offer renewable chemistry but often require formulation strategies to ensure robust field performance. Here we evaluate (−)-(S)-palasonin (PLN), a cantharidin analogue isolated from Butea monosperma (Lam.) Kuntze seeds, as a bioactive botanical insecticide and assess its synergistic effects when combined with multiple classes of insecticides against the cotton aphid Aphis gossypii Glover and green peach aphid Myzus persicae (Sulzer). Using a standardized leaf-dip assay, PLN showed high intrinsic activity (48 h LC₅₀ = 31.22 mg L⁻¹ for A. gossypii; 102.86 mg L⁻¹ for M. persicae). Preliminary LC₅₀-equivalent screens and fixed-ratio designs identified robust ratio-dependent enhancement with multiple chemistries. Quantitative co-toxicity coefficients (CTC) at empirically optimized ratios confirmed marked synergism in A. gossypii-notably with acetamiprid (CTC = 628.7) and imidacloprid (548.5)-and pronounced synergy in M. persicae with acetamiprid (272.2) and imidacloprid (265.1); λ-cyhalothrin was moderately synergistic (e.g., CTC = 203.5 in A. gossypii; 142.6 in M. persicae). The PLN-spirotetramat mixture was additive in M. persicae (CTC = 81.4), and PLN-flonicamid showed no synergistic optimum in that species. In a randomized complete block field trial conducted in Aksu, Xinjiang, China, the PLN co-formulations showed significantly higher Henderson-Tilton-corrected efficacy against A. gossypii than the single agents at 3–5 days after treatment(DAT). Collectively, these findings indicate that PLN is a bioactive botanical insecticide derived from an industrial crop that delivers robust dose-sparing benefits through synergistic interactions when combined with conventional insecticides, providing a practical route to strengthen aphid control while supporting integrated pest-management goals.