Peculiar structural features of midgut symbiotic organ in the early development of the stinkbug Plautia stali Scott, 1874 (Hemiptera: Pentatomidae).

Many insects have symbiotic microorganisms within their body. Such microbial symbiosis underpins the survival and prosperity of insects through multiple means. The brown-winged green stinkbug Plautia stali, which is notorious as an agricultural pest and utilized as an experimental model insect, harbors a bacterial symbiont Pantoea in a posterior part of the midgut, which is essential for the host's development and reproduction. From both basic and applied research perspectives, it is important to investigate the mechanistic bases underpinning the insect-microbe symbiotic association. Here, we performed detailed electron and optical microscopic analyses of the early nymphal midguts to reveal the type of cellular structure and property that orchestrates the symbiont colonization in the restricted part of the midgut. We identified two peculiar structural features of the nymphal midgut that develop in a region-restricted manner: long and heterogenous cellular protrusions (microvilli) solely emerged in the midgut symbiotic region and highly developed circular muscle cell layers specifically observed in the junction of non-symbiotic and symbiotic regions of the midgut. We discuss the potential roles of these unique structures in the midgut bacterial symbiosis.