The high annual production and use of cerium(IV) oxide nanoparticles (nCeO2s) may lead to their atmospheric release and substantial deposition on plants. This poses a potential threat to pollinators. We investigated the effects of nCeO2-spiked food (2–500 mg L−1) on summer and winter honeybees (Apis mellifera carnica) after chronic 9 days’ oral exposure.(304 characters)