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

Abstract

Simple Summary Biological invasions drive biodiversity loss, ecosystem degradation, and substantial economic costs globally. A key question is why a few introduced plants become invasive while others fail. This review examines three main explanations centred on plant–insect interactions: escape from natural enemies, production of novel suppressive chemicals, and evolutionary shifts from defence to growth. Our synthesis shows these mechanisms often interact synergistically, with their importance varying across species, communities, and environments. We argue that understanding invasions requires moving beyond pairwise interactions to embrace entire food webs, including soil biota, herbivores, and their natural enemies, as invasions trigger cascading effects across trophic levels. From this integrated perspective, we propose a biological control framework that prioritises local food-web integrity, complementary natural enemy deployment, and the use of molecular tools and predictive models for improved risk assessment. This review provides researchers and land managers with a practical, evidence-based framework for developing sustainable invasive species management strategies under current and future environmental change.