Fitness related effects of titanium dioxide nanoparticles and glyphosate exposure on Cardiocondyla obscurior

Insects are essential for ecosystem functioning and their rapid decline is alarming. While it is evident that various pollutants such as pesticides play a crucial role in the disappearance of insects, knowledge on the effects of specific inorganic compounds such as nanoparticles (NPs) are less investigated and little is known about their direct and indirect impacts. Titanium dioxide nanoparticles (TiO ₂ NPs) have seen a vast manufacturing increase over the last years and are abundantly found in the environment. However, the effects of TiO ₂ NPs on insects is little known, as well as their role as vectors for other chemical stressors. In this study, we investigated lethal and sublethal effects of TiO ₂ NPs on Cardiocondyla obscurior ants in two different settings. First, we examined its direct effects and second, we studied the combined effects when applied together with the herbicide glyphosate. We measured survival, brood production, gut endosymbiont densities, reactive oxygen species (ROS) accumulation, morphological features and elemental TiO ₂ distribution in ants chronically exposed to TiO ₂ NPs and/or glyphosate. The applied concentration mimicked environmentally realistic concentrations of the two pollutants. We found that proportional brood distribution was altered by the presence of the stressors. Moreover, we observed a synergistic effect between TiO ₂ NPs and glyphosate where the symbionts densities and TiO ₂ NPs accumulation were altered. These results shed light on the consequence TiO ₂ NPs ingestion and highlight the importance of understanding the synergistic effects of pollutants.