Functional roles of aphid-associated microbes in multitrophic interactions

• Aphid endosymbionts regulate host nutrition, fitness and resistance to biotic and abiotic stresses. • Microbes in aphid saliva and honeydew mediate plant defenses. • Honeydew-associated microbial volatiles can modify the behaviour of natural enemies. Aphids (Hemiptera: Aphididae) are economically important pests of crops worldwide. Although increasing evidence suggests that aphid-associated microorganisms have potential applications in integrated pest management (IPM), our understanding of their roles in multitrophic interactions remains limited. This review synthesizes current knowledge on aphid-associated endosymbionts and secretion-associated microbes, focusing on their influence on aphid physiology, behavior but also on interactions with host plants and natural enemies. Firstly, the functional diversity of endosymbionts, which contribute to improved nutrition, heat tolerance and resistance to pathogens, parasitoids and pesticides was highlighted. Secondly, we examined how microbes from aphid saliva and honeydew can act as molecular cues to induce plant defenses and modify the behaviour of aphidophagous beneficials. Special attention was given to honeydew-associated microbial volatiles (mVOCs), which can modulate the behavior of predators and parasitoids. Finally, emerging biocontrol strategies that leverage symbionts and mVOCs were discussed to propose future directions for integrating microbial ecology into sustainable aphid management.