Abstract:  Mutualism between microorganisms and animals plays a crucial part in the adaptation and evolution of hosts. Phloem-feeding aphids engage in intimate symbiotic associations with a variety of symbionts. Many aphid species cause enormous damage to crops, fruit trees, forest trees and medicinal plants, and some of them are important worldwide quarantine pests. Studies on aphid symbionts will advance our knowledge of symbiotic relationships between organisms and provide theoretical guidance for green pest management. Almost all aphid species harbour the primary symbionts to supply nutrients such as essential amino acids and vitamin B lacking in their diets. Secondary symbionts are closely related to the ecological adaptation of aphids. In this review, we outlined the species, tissue localization, transmission modes, and functions of aphid symbionts, and systematically summarized the species composition of symbiont communities in different groups of Adelgidae, Phylloxeridae and Aphididae. To date, most studies on aphid symbiont diversity have focused on different biotic and abiotic factors influencing the symbiont community structure, including aphid species, biological characteristics, evolutionary history, host plants, geographical distribution, and environmental factors (e.g., temperature). In the future, research should undertake extensive surveys of symbiont diversity across a greater variety of aphid taxa, enhance attention to gut symbionts, explore the relative contributions of stochastic and deterministic processes in the assembly of aphid symbiont communities, identify core symbionts and their biological functions, and focus on the potential application of key symbionts in RNAi-based biopesticides, so as to facilitate the development of efficient and environmentally friendly aphid pest management strategies.

Key words: Aphids, symbiotic microorganisms, phytophagous insects, agricultural and forestry pests, microbial community composition, microbial community structure, pest control