Efficacy assessment of Sericea lespedeza treatments on insect mortality and dose optimization using log-logistic modeling

Stored product pests, such as the maize weevil, Sitophilus zeamais Motchulsky (Coleoptera: Curculionidae), and Indianmeal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae) cause significant economic losses by infesting stored grains and reducing their quality. Botanical insecticides are gaining attention as safer alternatives to synthetic chemicals. Sericea lespedeza (Lespedeza cuneata), a perennial legume rich in condensed tannins, has shown potential as a bioactive plant for pest suppression. This study evaluated the efficacy of varying botanical treatment amounts on insect mortality and identified the optimal lethal dose using a dose-response approach. Treatments included leaf and seed powders of S. lespedeza at different concentrations (0.5, 1, and 2g), as well as a monoterpenoid used as a positive control. A completely randomized design was implemented across multiple trials and days, assessing mortality under these treatments and their different concentrations. Mortality data were analyzed through a combination of ANOVA, Kruskal-Wallis testing, and nonlinear regression modeling. Results indicated a significant interaction between treatment type and dose (ANOVA p < 0.001), with Kruskal-Wallis confirming group-level differences (H = 177.63, p < 0.0001). The dose-response curve fitted with a log-logistic model estimated the LD₅₀ at approximately 10g. Principal Component Analysis and Kmeans clustering further revealed treatment-specific grouping patterns based on mortality, dead, and alive counts. Overall, this work provides evidence for the effectiveness of select botanical treatments and highlights 10g as the most efficient dose for achieving 50% mortality. These findings contribute to developing sustainable insect pest management strategies in stored product protection.