ABSTRACT
Species in the Hemiptera (insect order) have engaged in obligate heritable symbioses with various microbes for >350 million years. Such symbioses have permitted hosts to exploit niches that are otherwise unsuitable for animal life to persist. In general, microbes provide their hosts with essential nutrition that hemipteran insects are unable to synthesize or acquire from their specialized diets (e.g., plant saps and mammalian blood). They also provide other beneficial services, including immune system priming, cuticle formation, and chemical defenses. Hemipteran hosts have evolved a wide range of mechanisms to faithfully transmit their symbionts between host generations and to regulate their cellular and metabolic functions. Specifically, many species in the Heteroptera (suborder) inherit their symbionts externally often through maternal deposits and maintain them specialized midgut regions. In contrast, most other hemipteran species restrict their symbionts to specialized host cells and organs and transmit them directly within the mother. Despite these differences, hemipteran symbionts generally undergo genome streamlining and degradation. In the most extreme cases, symbionts lose >90% of their genes. In order for hosts to maintain stable symbioses, they must evolve dynamic support mechanisms. Thus, studies of hemipteran symbioses have provided important insights into how hosts establish and maintain beneficial symbioses.
