The diverse locations of endosymbionts in insects. The locations of the endosymbionts are shown in these schematic diagrams by red dots. (a) 1, The bee-wolf Philanthus triangulum harbors endosymbionts within the antennal segments . 2, Bacteriocytes carrying primary endosymbionts can be localized within the midgut epithelium (carpenter ants) or in an organ-like structure called the bacteriome, which comprises a collection of bacteriocytes, located adjacent to the midgut (for example, in weevils, aphids and whiteflies) [6,7]. 3, Primary endosymbionts may also be present in the ovaries to ensure vertical transmission [6,7]. 4, Cockroaches and the termite Mastotermes darwiniensis harbor endosymbionts in a bacteriome within the fat body . (b) Acanthosomatid stinkbugs harbor extracellular endosymbionts in crypts in a specialized part of the midgut (m4). The midgut is differentiated into four parts (m1 to m4) whereas the hindgut has a simple structure . (c) Termites harbor a complex symbiotic community in their hindgut lumen . In contrast to stinkbugs, the hindgut but not the midgut is differentiated into several parts with differing chemical milieux. MT, malpighian tubules.