Microplastics and Nanoplastics Alter the Physicochemical Properties of Willow Trees and Lead to Mortality in Leaf Beetle Larvae

ABSTRACT Polystyrene micro‐ and nanoplastics (MNPs) are increasingly found in terrestrial environments, posing risks across the food web. However, the potential impacts of MNPs transfer on plant‐insect interactions remains largely unknown. In this study, consumption of willow plants ( Salix maizhokunggarensis ) exposed to 10.0 mg/L MNPs for 21 days inhibited survival and reduced body weight in Plagiodera versicolora larvae unlike those exposed to lower concentrations or shorter durations (0.1, 1.0 and 10.0 mg/L MNPs for 7 or 14 days). MNPs exposure increased lignin content and leaf thickness in willows, leading to decreased leaf consumption and increased mouthpart wear in P. versicolora larvae. Transcriptome and gut microbiota analyses revealed significant downregulation of genes related to digestion, intestinal homoeostasis, immunity, and growth/development along with profound alterations in gut microbiota composition. Notably, the abundance of the pathogenic bacterium Pseudomonas increased significantly. The gut barrier was disrupted, allowing gut bacteria to translocate into the haemolymph, accelerating larval mortality. Overall, MNPs altered plant physiology, making willow plants unsuitable for herbivore consumption and indirectly influenced herbivore survival by modulating gut bacteria. These findings offer novel insights into the cascading ecological effects and risks of MNPs, highlighting potential impacts on plant‐herbivore interactions, biodiversity, and ecosystem health in terrestrial ecosystems.