Fungicide consumption exacerbates the negative effects of a common gut parasite in bumble bee

Bumble bees face numerous environmental stressors, including gut-parasite
infection and exposure to agricultural fungicides, which can negatively
impact colony health. This study evaluates the interactive effects of
these stressors on bumble bee (Bombus impatiens) microcolonies, focusing
on colony development, worker survival, and parasite infection dynamics.
Our aim in evaluating these interactions was to determine if bees would
experience synergistic negative health outcomes compared to single
stressor exposures. We reared forty queenless bumble bee microcolonies,
and treated them with either fungicide-contaminated pollen, inoculation
with a gut parasite, both, or neither. Contrary to original expectations,
we did not observe significant synergistic interactions between the two
stressors, however we found that consumption of fungicide was associated
with higher likelihood of gut-parasite infection, and delayed recovery
from infection. Fungicide consumption was also connected to smaller
workers, and smaller male offspring. We also found that gut-parasite
infection was correlated with decreased pollen consumption overall,
decreased worker survival, and fewer developed pupae. This study provides
insights into the impacts of co-occuring stressors affecting bumble bees
and emphasizes the importance of sublethal effects on pollinator health.