The Multifaceted Effects of Melia azedarach Leaf Extract on Galleria mellonella: Enzymatic, Histological, and Ultrastructural Investigations

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