SD03: Double trouble: Fungicide consumption and parasite infection negatively affect bumble bees

Multiple populations of native North American bumble bees are declining. The reasons for this decrease are varied, and it's probable that combined effects of multiple stressors are worsening the situation. We investigated the combined and independent effects of fungicide consumption and Crithidia bombi infection on the health of queenless common eastern bumble bee microcolonies. We exposed 45 microcolonies of five bumble bee workers to either fungicide-contaminated pollen, Crithidia bombi infection, both, or neither. We recorded the number and size of males successfully emerged within each colony, composition of brood cells, worker mortality and size, and pollen consumption of each microcolony. We found that consumption of fungicide was correlated with longer times until first male emergence. We found that infection with C. bombi was correlated with smaller workers, fewer live pupae within brood cells, and males produced in infected microcolonies had significantly higher relative fat content. Microcolonies exposed to both stressors consumed less pollen and were associated with increased worker mortality. These findings have important implications for bumble bee pollination services and population health in urban and agricultural areas experiencing increases in fungicide application.