Plant–Insect Interactions in Biological Invasions: From Classical Hypotheses to Multitrophic Networks and Biological Control

Biological invasions are a critical driver of global environmental change, with plant–insect interactions central to invasion success and biological control. This review systematically examines three classical hypotheses—the Enemy Release Hypothesis (ERH), the Novel Weapons Hypothesis (NWH), and the Evolution of Increased Competitive Ability (EICA) hypothesis, within a plant–insect context. Our synthesis shows that ERH support is widespread but highly contingent on environmental context; NWH highlights the negative effects of invasive allelochemicals on native insects and soil biota; and the EICA hypothesis provides an evolutionary framework for understanding shifts in defence–growth resource allocation in invasive plants. We advocate for a multitrophic network perspective that captures ecosystem complexity and elucidates synergistic interactions among hypotheses across space and time. We identify inherent limitations in single-hypothesis biocontrol approaches and propose an integrative management framework grounded in network theory. Emerging tools—including molecular ecology and network modelling—are emphasised for resolving cryptic interactions and forecasting control outcomes. Future priorities include interdisciplinary integration, long-term monitoring, global comparisons, and addressing climate-driven uncertainties. This review aims to advance both theoretical invasion ecology and the development of sustainable, evidence-based biological control strategies.