Acute exposure to environmental doses of di-n-butyl phthalate but not di-2-ethylhexyl phthalate induces mortality in isolated and cold-stressed workers of Bombus terrestris L. (Hymenoptera: Apidae)

Since the past decades, declining trends in bee populations have been reported worldwide. Among multiple anthropogenic factors, endocrine disruptors, such as phthalates, could negatively affect bees and contribute to this decline at environmental level of exposure. Yet, no data are available on phthalate toxicity in bees. Di-2-ethylhexyl phthalate (DEHP) and di-n-butyl phthalate (DnBP), widely used as plasticisers and adjuvants, are some of the most commonly recorded phthalates in the environment, including on social bee worker cuticles. In this study, we investigated DnBP and DEHP lethal effects on B. terrestris workers after contact exposure to environmentally relevant single-molecule and mixture treatments. Interactions with cold stress and social context were additionally investigated. Firstly, we evidenced for the first time an NMDRC for DnBP toxicity in bees, with an increased mortality of 25 %, 72 h after exposure. By contrast, DEHP did not affect worker survival and even lowered DnBP toxicity when administered as a mixture. Secondly, DnBP at low environmental doses enhanced worker resistance to cold stress, while exposure to cold stress modulated DnBP toxicity, shifting the onset of adverse effects to higher concentrations. Finally, we evidenced that social contacts mitigate DnBP toxicity. Overall, this study provided the first evidence of the detrimental effects caused by these overlooked pollutants on bees, and discusses potential metabolic disruption by phthalate exposure that may affect crucial life traits in bumblebees. Finally, this study highlighted that accounting for complex realistic mixtures and the social context of the studied species seems essential for accurately assessing the toxicity of endocrine disrupting molecules.