Fig. 4
Development of the symbiotic organ and colonization process of the symbiotic bacteria in P. stali. a Dissected symbiotic organs at different developmental stages: 1st day-1, first instar nymph 1 day after hatching; 2nd day-1, second instar nymph 1 day after molting; 3rd day-1, third instar nymph 1 day after molting; 4th day-1, fourth instar nymph 1 day after molting; 5th day-1, fifth instar nymph 1 day after molting; 5th day-7, fifth instar nymph 7 days after molting; Adult day-1, adult insect 1 day after eclosion. b-g Enlarged bright-field images of the symbiotic midgut. Note that the crypts are obscure at the first instar and become evident at later stages. h–l FISH visualization of the symbiotic bacteria on longitudinal tissue sections of the midgut symbiotic organ. Note that the crypts are obscure and the symbiotic bacteria are sparse at the first instar, whereas the crypts are evidently formed and densely populated by the symbiotic bacteria at later stages. b, h First instar nymphs 1 day after hatching. c, i Second instar nymphs 1 day after molting. d, j Third instar nymphs 1 day after molting. e, k Fourth instar nymphs 1 day after molting. f, l Fifth instar nymphs 1 day after molting. g Fifth instar nymphs 7 days after molting. m Fifth instar nymph 7 days after molting. In h–m, blue and red signals indicate host’s nuclear DNA and symbiotic bacteria, respectively