Integrative Morphometric and Molecular Characterization of Diarrhegma modestum (Fabricius, 1805) (Diptera: Tephritidae) Demonstrates Evolutionary Cohesion and Implications for Sustainable Pest Management

Fruit fly infestations pose a persistent threat to tropical fruit production, yet integrative morphometric and molecular studies remain limited for emerging Tephritid pests in South Asia. Diarrhegma modestum (Fabricius, 1805) (Diptera: Tephritidae) is a recently re-emerging species attacking Cucurbita maxima , Trichosanthes cucumerina , Luffa acutangular , Mangifera indica , Psidium guajav a and other hosts, but its morphological variability, genetic stability, and evolutionary position have not been comprehensively characterized. This study bridges that knowledge gap by integrating morphometric, multivariate, and molecular phylogenetic analyses to define intraspecific structure and evolutionary relationships of D. modestum populations from South India. Morphometric evaluation revealed pronounced sexual dimorphism, with females exhibiting the largest size difference in whole-body length (6.41 mm) compared to males (5.16 mm). Principal Component Analysis (PCA) explained 56.95% of total variance, identifying head width, thorax width, wing width, and antenna length as positively correlated traits forming a dominant “size-breadth” axis associated with flight and reproductive performance. The mitochondrial COI sequence analysis (682 bp) confirmed 97.8–99.2% identity with reference D. modestum accessions, while Bayesian and chronogram analyses dated the Diarrhegma–Carpomya divergence to 9–11 Mya, reflecting moderate substitution rates (0.1567 subs/site/unit time) and neutral evolution. By linking morphometric differentiation with genetic stability, this study establishes a diagnostic and evolutionary framework for sustainable pest management. The integrative characterization enables oviposition-targeted surveillance, female-biased baiting, and molecularly validated monitoring. Together, these insights provide a foundation for precision-based, eco-adaptive strategies that strengthen fruit-fly management and support resilient tropical agroecosystems.