Aphid adaptation in a changing environment through their bacterial endosymbionts: an overview, including a new major cereal pest (Rhopalosiphum maidis (Fitch) scenario

Aphids (Hemiptera: Aphididae) are small, phloem-feeding insects that exhibit remarkable adaptability and resilience to various environmental conditions, including heat stress. Recent research has shed light on the role of bacterial symbionts in influencing the heat tolerance of aphids. Additionally, an intriguing avenue of investigation has explored how aphids can acquire bacterial symbionts through a unique mechanism involving soil nematodes. In this paper, we provide an in-depth overview of the interplay between heat stress, bacterial symbionts, and soil nematodes in the context of aphid biology. In reviewing the existing literature and collating available knowledge, we highlight the mechanisms by which bacterial symbionts contribute to aphid heat stress tolerance and examine the symbiont acquisition process facilitated by soil nematodes. Furthermore, we discuss the implications of these symbiotic associations in relation to the ecology, evolution, and agricultural management of a major globally expanding pest aphid, the corn leaf aphid, Rhopalosiphum maidis (Fitch). Overall, it may be concluded that both primary and secondary bacterial endosymbionts play a significant role in aphid biology with evolutionary consequences. These include adaptations through bacterial symbionts in terms of longevity and fecundity, heat shock tolerance, and resistance to fungal pathogens and primary hymenopterous wasp parasitoids.