Structural remodeling of midgut symbiotic organ and altered food flow upon metamorphosis of the stinkbug Plautia stali

Animals possess a mouth for feeding, an anus for defecation, and a gut structurally and functionally connecting them for digestion and absorption. In some stinkbugs, strikingly, the mouth and the anus are functionally disconnected in the middle. The constricted region blocks food flow and selectively allows passing of a specific bacterial symbiont to maintain the posterior midgut region as an exclusive space for symbiosis. In the stinkbug Plautia stali, the constricted region was reported to open during the last nymphal instar, thereby restoring the normal gut passage in adult insects. Here, we experimentally investigated how the structural gut reorganization upon metamorphosis of P. stali affects the processing of liquid food and solid food using blue coloring and fluorescent microbeads. In nymphal insects, both coloring and microbeads were blocked at the constricted region, and only coloring was excreted to the hindgut via Malpighian tubules. In adult insects, both coloring and microbeads passed through the constricted region and excreted to the hindgut. These results suggested that nymphal P. stali can utilize liquid food only whereas adult P. stali can live on both liquid food and solid suspension food, which may be relevant to nutritional and reproductive differences between nymphal and adult stinkbugs.