Diversity of bacterial symbiosis in stinkbugs

Many animals and plants establish symbiotic associations with benevolent microorganisms. In particular, most of insects that feed exclusively on restricted diets, such as plant sap, vertebrate blood or woody material, usually possess symbiotic microorganisms inside their body. Recent studies have suggested that more than 50% of insect species may be benefited from such endosymbiotic partners. Among these insects, members of the Heteroptera, known as true bugs or stinkbugs, exhibit an extraordinary diversity in their microbial symbiotic system. Such diversity is exemplified by: (i) physiological impact of the symbiotic associations on the host fitness ranging from parasitic to mutualistic; (ii) interdependence of the symbiotic associations ranging from facultative to obligate; (iii) location of the symbiont ranging from extracellular in gut cavity to intracellular in specialized cells; (iv) among the extracellular associations, specialized symbiotic structures such as midgut sacs and tubular outgrowths, whose cavity harbors specific symbiotic bacteria, varying in their number and arrangement; and (v) mechanisms for symbiont transmission ranging from vertical to environmental. Here, the current biological knowledge of the diverse stinkbug-bacteria symbioses is reviewed, which will provide novel insights into and useful model systems for understanding of the host-symbiont interactions and evolution.