Abstract: Insects always harbor diverse microbial symbionts at certain development stages, which play significant roles in growth, reproduction, and adaption to environments and coevolution with their hosts. As demonstrated in numerous studies, these symbionts do not stay or work alone but instead have established certain relationships with each other. Here we reviewed the major findings reported in the past decade regarding interactions among symbiotic bacteria of various groups, as well as the relations between symbiotic bacteria and other microbes including bacterial, fungal and virus pathogens and fungal symbionts. We focused on the cooperation between co-infecting symbiotic bacteria that complementarily confer beneficials to hosts, realized or possibly ongoing replacement of bacteria by the ones more recently infecting insects, and effects of bacterial symbionts on the susceptibility of hosts to pathogens. The research prospects on symbiotic bacteria were discussed with the consideration of applying various biotechnology in this field.

Key words: bacteria, symbiotic systems, bacterial replacement, pathogens, biological control