The evolutionary arms race between plants and herbivorous insects is a complex process that has developed multiple facets over time. Recent studies have increasingly highlighted the role of symbiotic microorganisms in this dynamic co-evolutionary contest. The insect gut serves as a crucial interface for herbivore-plant interactions, and is also the primary habitat for symbiotic microorganisms. These microorganisms influence plant-insect interactions on several levels. First, they can provide essential nutrients that plants may not provide to herbivores. Second, insects often rely on these symbionts to cope with the defensive strategies of their host plants, including the manipulation of defense signaling pathways and the detoxification of harmful compounds. Finally, gut microbes play a significant role in tritrophic interactions between host plants, herbivorous insects and natural enemies. In this article, we review the arms race between plants and insects and emphasize how gut microorganisms help insects counter plant defenses. Furthermore, we discuss cutting-edge methodologies employed to study insect-symbiont interactions and explore the potential applications of gut microbiome research in integrated pest management.