<b>The Multifaceted Effects of </b><b><i>Melia azedarach</i></b><b> Leaf Extract on </b><b><i>Galleria mellonella</i></b><b>: Enzymatic, Histological, and Ultrastructural Investigations</b>

The rising demand for sustainable pest management has increased interest in plant-derived biopesticides as environmentally friendly alternatives to synthetic insecticides. This research assessed the insecticidal potential of Melia azedarach leaf extract (MLE) against Galleria mellonella larvae through comprehensive phytochemical, toxicological, and physiological analyses. Phytochemical screening indicated substantial polyphenolic content with total phenolic (42.06 ± 1.12 mg GAE/g), flavonoid (16.96 ± 1.42 mg QE/g), and condensed tannin (9.46 ± 0.49 mg CE/g) contents. HPLC analysis detected sixteen phenolic and flavonoid substances, with kaempferol and quercetin as major constituents. Acute toxicity assessment via ingestion demonstrated dose-dependent mortality with an LD50 /10days of 1.39 mg g⁻¹ body weight. Sublethal exposure (LD25) markedly disrupted developmental parameters, prolonging larval and pupal development and diminishing pupal weight and fecundity. All investigated midgut enzymes showed significant activity decline, with lysozyme exhibiting the most pronounced reduction (68.13%); carbohydrate digestive enzyme activity (α-amylase, α-glucosidase, β-glucosidase, β-galactosidase) reduced in the range of 42–60%, while protein digestive enzyme activity (trypsin, chymotrypsin, carboxypeptidase, cysteine protease, leucine aminopeptidase) reduction was in the range of 34–53%. Histological and ultrastructural analyses demonstrated extensive midgut epithelial damage, including vacuolization, cellular degeneration, and microvilli disruption. Thus, M. azedarach seems to possess a battery of insecticidal mechanisms that establish it as an eco-friendly biocontrol agent under integrated pest management strategies随着可持续害虫治理需求的日益攀升，植物源生物农药作为合成杀虫剂的环保替代方案，受到了广泛关注。本研究通过全面的植物化学、毒理学与生理学分析，评估了楝（Melia azedarach）叶片提取物（MLE）对大蜡螟（Galleria mellonella）幼虫的杀虫潜力。植物化学筛选结果显示，该提取物含有丰富的多酚类物质，其中总酚含量为42.06 ± 1.12 mg GAE/g、总黄酮含量为16.96 ± 1.42 mg QE/g、缩合单宁含量为9.46 ± 0.49 mg CE/g。高效液相色谱（High Performance Liquid Chromatography, HPLC）分析共检测出16种酚类与黄酮类物质，其中山奈酚（kaempferol）与槲皮素（quercetin）为主要成分。经口染毒的急性毒性评估结果显示，幼虫死亡率呈剂量依赖性，10天半数致死剂量（Lethal Dose 50, LD50）为1.39 mg g⁻¹ 体重。亚致死剂量（LD25）暴露则显著干扰了昆虫的发育参数，延长了幼虫与蛹的发育时长，降低了蛹重与繁殖力。所有被测中肠酶的活性均出现显著下降，其中溶菌酶活性降幅最为明显（68.13%）；碳水化合物消化酶（α-淀粉酶、α-葡萄糖苷酶、β-葡萄糖苷酶、β-半乳糖苷酶）活性降幅介于42%~60%之间，而蛋白质消化酶（胰蛋白酶、胰凝乳蛋白酶、羧肽酶、半胱氨酸蛋白酶、亮氨酸氨肽酶）活性降幅则处于34%~53%范围内。组织学与超微结构分析结果显示，中肠上皮细胞出现广泛损伤，包括空泡化、细胞变性以及微绒毛破坏。综上，楝提取物具备多重杀虫作用机制，可作为害虫综合治理（Integrated Pest Management, IPM）策略下的环保型生物防治制剂。