Nanoscale 3D anatomy of the western flower thrips reproductive system revealed by volume electron microscopy: extreme miniaturization and evolutionary adaptations for pest fecundity

Frankliniella occidentalis (western flower thrips, WFT) is a globally destructive pest causing major crop losses via oviposition, feeding, and plant virus transmission. Previous work has focused on its reproductive physiology and behavior, but comprehensive 3D structural knowledge remains limited. We used volume electron microscopy (vEM) to achieve nanoscale 3D visualization of the reproductive systems in both sexes, providing the first high-resolution, in situ reconstruction and establishing a new anatomical framework for insect reproductive physiology. Males exhibit extreme miniaturization, with reproductive organs occupying just 1.45 % of body volume yet retaining full function within a compact abdomen. Females possess eight tightly interwoven ovarioles that maximize coelomic space for oocyte maturation, maintaining a slender form while housing large eggs-reflecting an evolutionary trade-off between reproductive efficiency and body size. Our reconstructions resolve a key ambiguity: the female accessory glands are a pair of fused, S-shaped structures joined by an internal duct opening near the ovipositor base. Quantitative analysis reveals the first complete germ cell census, with asymmetric ovary cell numbers suggesting an adaptive strategy for sustained fecundity. By integrating detailed morphology with systematic quantification, this study creates a foundation for research in functional morphology and for developing reproduction-targeted pest management. The structural insights enable precise strategies to disrupt thrips reproduction and reduce virus spread. Beyond advancing pest control innovation, the findings serve as a valuable educational and reference resource in insect morphology.