3D reconstruction of the ovariole in Nilaparvata lugens (Hemiptera: Delphacidae) by FIB-SEM.

The brown planthopper (Nilaparvata lugens) has a high reproductive rate, posing a significant challenge to biological control of rice pests. This is largely due to the physiological and functional traits of its telotrophic ovarioles, which feature a centralized nutrient supply to ensure each oocyte obtains essential basic nutrients. Current studies on insect ovarioles primarily focus on hormonal regulation and gene expression; the cellular composition and spatial relationships within N. lugens ovariole tissues remain poorly understood. To illustrate the internal architecture of ovarioles and the intricate oogenesis process at nanoscale resolution, this study employed focused ion beam-scanning electron microscopy for 3D volume reconstruction, overcoming limitations of traditional 2D electron microscopy. Using this advanced imaging technique, we systematically characterized key ovariole components including terminal filaments, trophocytes, germ cell clusters, three types of follicular cells, nutritive cords, and oocytes. Our findings reveal that rather than maintaining a continuous linkage, the nutritive cord transiently connects to the oocytes during specific developmental stages to facilitate nutrient transfer. An assembly of unique, cake-like phospholipoglycoproteins was identified within the oocytes, suggesting specialized energy storage mechanisms. The detailed 3D model elucidates the spatial relationship and relative position between various parts of the ovariole, offering novel insights into the mechanisms of oocyte growth and nutrient acquisition. These findings advance foundational knowledge of insect reproductive biology and provide a valuable framework for future research on pest control strategies targeting N. lugens reproduction.