Ecotoxicology of microplastic contamination: insights into the pest defense of Ulmus pumila and pest control efficiency of Bacillus thuringiensis.

BACKGROUND The situation of microplastic pollution in terrestrial ecosystems is becoming increasingly severe. This study developed a polyethylene (PE) microplastic-contaminated soil-Ulmus pumila-Hyphantria cunea larvae food chain model to investigate the ecotoxicological impacts of soil microplastic pollution from the perspective of pest occurrence and pest control. RESULTS After feeding on PE-treated U. pumila leaves, the body weight, body length, head capsule width and nutrient content of H. cunea larvae were significantly reduced, accompanied by disrupted expression levels of growth regulatory genes. PE stress significantly reduced the content of nutrients and chlorophyll in U. pumila leaves and inhibited the expression of key genes in glucose and amino acid metabolism pathways. PE treatment also significantly reduced the content of secondary metabolites (flavonoids and total phenolics) and the expression levels of key genes in the flavonoid synthesis pathway (e.g., FLS and CHS) in the leaves. The combined treatment of PE and Bacillus thuringiensis (Bt) significantly increased the mortality and weight inhibition rate of H. cunea larvae in a synergistic manner. The combined treatment of PE and Bt aggravated the breakdown of innate immunity in larvae, including cellular and humoral immunity. PE and Bt combined treatment significantly increased the expression of apoptosis genes in larval midgut, as well as decreased the nutrient content and energy metabolism gene expression levels of larvae compared with Bt treatment alone. CONCLUSION Microplastic pollution reduces the defense of U. pumila against H. cunea larvae in a self-damaging manner, and Bt proves effective for controlling H. cunea larvae in microplastic-contaminated environments. © 2025 Society of Chemical Industry.