Enhanced polyphenolic production in tissue culture-derived Opuntia ficus-indica increases larvicidal activity against Spodoptera exigua: biochemical, histological and molecular docking evidence
The accelerating resistance of Spodoptera exigua to synthetic insecticides demands the development of eco-friendly botanical alternatives. Plant tissue culture provides a controlled means to enhance the biosynthesis of defense metabolites. This study explored how in vitro micropropagation can enhance the polyphenolic profile and insecticidal efficacy of Opuntia ficus-indica cladode ethanolic extracts. These extracts, cultured on Murashige and Skoog medium without (Op1) or with plant growth regulators (Op2), were compared with greenhouse-grown (Op3) extracts for activity against second- and fourth-instar S. exigua larvae. Phytochemical analyses revealed differences among the extracts. The Op2 extract exhibited the highest total phenolic content (61.1 mg GAE g−1) and flavonoid content (131.95 mg QE g−1). HPLC profiling revealed that Op2 had higher levels of gallic acid (26.94 µg mg−1) and kaempferol (17.26 µg mg−1), whereas the greenhouse-grown extract was dominated by catechin and gallic acid. Bioassays showed that Op2 was the most toxic, with LC50 values of 4.87 and 2.70 mg mL−1 for the second and fourth instars, respectively. Biochemical assays revealed metabolic disruption, indicated by a significant elevation in lactate dehydrogenase (LDH) activity (up to 5.20-fold) and a suppression of glutathione peroxidase (GPx) activity (up to 82.18%). Histopathological examination confirmed severe damage to the integument and midgut tissues. Molecular docking analysis indicated that kaempferol exhibited the highest binding affinity for LDH and GPx (− 6.32 and − 6.72 kcal mol−1, respectively), while ferulic acid showed strong binding (− 6.12 and − 6.15 kcal mol−1, respectively). These findings identify tissue culture-enhanced O. ficus-indica as a promising biopesticide for pest management.