Repeated exposure of bumblebee workers to field-realistic doses of di-2-ethylhexyl and di-n-butyl phthalates lowers worker survival and induces obesity-related phenotypes in workers and brood.

Wild bees, like many other insects, are declining. Multiple drivers have been identified, but the potential effects of endocrine disruptors such as phthalates, remain poorly studied. Yet, di-2-ethylhexyl phthalate (DEHP) and di-n-butyl phthalate (DnBP), two of the most common phthalates that pervade the environment, are known to affect key hormonal and metabolic pathways in invertebrates even at field realistic doses. These ubiquitous pollutants are semi-volatile compounds used to increase the flexibility of plastic materials, or as solvents for certain detergents, pesticides, and other products. Bees are notably exposed to these lipophilic molecules through their cuticle, with exposure varying in both quantity and chemical composition. To investigate the potential impacts of phthalate exposure, Bombus terrestris workers were repeatedly exposed (once per week) to nominal field-realistic doses of DEHP and DnBP and maintained in microcolonies during 35 days. Worker mortality and male emergence were recorded throughout the experiment. Offspring production was assessed in terms of number and mass, and abdominal lipid ratio was assessed in adults. Repeated exposure to DEHP increased worker mortality up to 50%, while DnBP increased worker lipid stores and offspring mass, suggesting potential metabolic disruption. These findings indicate that the two most common phthalates can have both lethal and sublethal effects on bees, likely through disruption of crucial physiological pathways, with cascading consequences for individual health and colony development even at environmental concentrations.