Specialized organs of Elasmostethus humeralis for harboring the symbiotic bacteria. (A) An adult female. (B) A dissected midgut: m1, midgut first section; m2, midgut second section; m3, midgut third section; m4, midgut fourth section with crypts; h, hindgut. (C) An enlarged image of the midgut fourth section, with butterfly-shaped symbiotic organ consisting of a number of crypts fused two-dimensionally. (D) A sectioned image of the symbiotic organ, stained with hematoxylin and eosin: c, midgut crypt; g, midgut main tract. (E) An in situ hybridization image of the symbiotic organ, wherein the symbiotic bacteria (red) and the insect nuclei (blue) are visualized. (F) A dissected ventral abdomen of a female insect, on which a pair of lubricating organs is seen (arrows). (G) An enlarged image of the lubricating organs (arrows) in the posterior tip of the abdomen. (H) A dissected lubricating organ, with the yellow membranous tissue surrounding the organ removed: r, chitinous ridge region; s, sac-like region. (I) An in situ hybridization image of the dissected lubricating organ, in which the symbiotic bacteria (red) are specifically detected in the sac-like region. Inset is a confocal image, showing tubulet-like structures harboring the symbiont. Bars, 2 mm in (A), 0.5 mm in (B), 0.2 mm in (C), 100 μm in (D) and (E), 1 mm in (F), 0.5 mm in (G), 0.25 mm in (H) and (I), and 100 μm in (I, inset).