Bioactivity and Molecular Responses of Bitter Gourd Leaf Extracts Against the Invasive Leafminer, Liriomyza trifolii (Diptera: Agromyzidae).

Liriomyza trifolii is a global pest of vegetables and ornamental plants and a major invasive species in China. Long-term irrational use of chemical insecticides has reduced control efficacy, driving interest in plant-derived alternatives. Bitter gourd, Momordica charantia, extracts show potential against various pests, but their effects on L. trifolii are unknown. To address this, host suitability tests were first conducted and revealed that L. trifolii exhibited significantly higher adaptability to kidney bean than to bitter gourd in terms of both oviposition and feeding, and failed to complete its life cycle on bitter gourd. Further treatment with ethanol extracts of bitter gourd leaves demonstrated dose-dependent adulticidal activity; at the LC50 concentration, the extract not only reduced feeding punctures and oviposition, but also significantly decreased egg hatching and larval survival, while showing no significant impact on pupation or emergence. To elucidate the underlying molecular mechanisms, integrative transcriptomic and metabolomic analyses were subsequently performed. Transcriptomics identified 254 differentially expressed genes (DEGs) enriched in ribosome, oxidative phosphorylation, and peroxisome pathways, and upregulated DEGs included a vitellin-degrading protease and cytochrome P450. Meanwhile, metabolomics detected 272 differential metabolites (DEMs): upregulated metabolites were linked to purine metabolism, while downregulated ones were associated with cysteine/methionine and arginine/proline metabolism. Integrated analysis revealed "Biosynthesis of amino acids" as the sole common pathway, with S-adenosyl-L-homocysteine, N-succinyl-LL-2,6-diaminoheptanedioate, and glutamine synthetase (Ltr05G008090) showing significant correlations. These findings suggest that reprogramming of amino acid and nitrogen metabolism may participate in the response and could serve as a candidate response pathway. Accordingly, this study may offer a theoretical basis for the future development of botanical insecticides based on bitter gourd leaf extract against L. trifolii.