Trophic Transfer of Metal Oxide Nanoparticles in the Tomato-<i>Helicoverpa armigera</i> Food Chain: Effects on Phyllosphere Microbiota, Insect Oxidative Stress, and Gut Microbiome

Understanding the trophic transfer and ecological cascade effects of nanofertilizers and nanopesticides in terrestrial food chains is crucial for assessing their nanotoxicity and environmental risks. Herein, the trophic transfer of La₂O₃ (nLa₂O₃) and CuO (nCuO) nanoparticles from tomato leaves to <i>Helicoverpa armigera</i> (Lepidoptera: Noctuidae) caterpillars and their subsequent effects on caterpillar growth and intestinal health were investigated. We found that 50 mg/L foliar nLa₂O₃ and nCuO were transferred from tomato leaves to <i>H. armigera</i>, with particulate trophic transfer factors of 1.47 and 0.99, respectively. While nCuO exposure reduced larval weight gain more (34.7%) than nLa₂O₃ (11.3%), owing to higher oxidative stress (e.g., MDA and H₂O₂) and more serious intestinal pathological damage (i.e., crumpled columnar cell and disintegrated goblet cell) by nCuO. Moreover, nCuO exposure led to a more compact antagonism between the phyllosphere and gut microbiomes compared to nLa₂O₃. Specifically, nCuO exposure resulted in a greater increase in pathogenic bacteria (e.g., <i>Mycobacterium</i>, <i>Bacillus</i>, and <i>Ralstonia</i>) and a more significant decrease in probiotics (e.g., <i>Streptomyces</i> and <i>Arthrobacter</i>) than nLa₂O₃, ultimately destroying larval intestinal immunity. Altogether, our findings systematically revealed the cascade effect of metal oxide nanomaterials on higher trophic consumers through alteration in the phyllosphere and insect gut microbiome interaction, thus providing insights into nanotoxicity and environmental risk assessment of nanomaterials applied in agroecosystems.