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 (TiO₂NPs) are abundantly found in the environment but their effects 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 TiO₂NPs on Cardiocondyla obscurior ants alone or combined with the herbicide glyphosate. We measured survival, brood production, gut endosymbiont densities, reactive oxygen species (ROS) accumulation, morphological features and elemental TiO₂ distribution in ants chronically exposed to environmentally realistic concentrations of TiO₂NPs and/or glyphosate. We found that proportional brood distribution was altered by the presence of the stressors and it was time dependent. Moreover, we observed a synergistic effect between TiO₂NPs and glyphosate with bigger newly produced queens, altered gut endosymbionts densities and accumulation of TiO₂NPs. These results shed light on the ecotoxicological effects of TiO₂NPs ingestion and highlight the importance of understanding the synergistic effects of pollutants.