Sunflower pollen reduces a gut pathogen in the model bee species, <i>Bombus impatiens</i> , but has weaker effects in three wild congeners

Abstract

Commercial bumblebees have become popular models to understand stressors and solutions for pollinator health, but few studies test whether results translate to other pollinators. Consuming sunflower pollen dramatically reduces infection by the gut parasite <i>Crithidia bombi</i> in commercially reared <i>Bombus impatiens</i>. We assessed the effect of sunflower pollen on infection in wild <i>B. impatiens</i>, <i>Bombus griseocollis, Bombus bimaculatus</i> and <i>Bombus vagans</i>. We also asked how pollen diet (50% sunflower pollen versus wildflower pollen) and infection (yes/no) affected performance in wild <i>B. impatiens</i> microcolonies. Compared to controls, sunflower pollen dramatically reduced <i>Crithidia</i> infection in commercial and wild <i>B. impatiens,</i> had similar but less dramatic effects in <i>B. bimaculatus</i> and <i>B. vagans</i>, and no effect in <i>B. griseocollis</i>. <i>Bombus impatiens, B. bimaculatus</i> and <i>B. vagans</i> are in the same subgenus, suggesting that responses to sunflower pollen may be phylogenetically conserved. In microcolonies, 50% sunflower pollen reduced infection compared to wildflower pollen, but also reduced reproduction. Sunflower pollen could control <i>Crithidia</i> infections in <i>B. impatiens</i> and potentially close relatives, but may hinder reproduction if other resources are scarce. We caution that research using managed bee species, such as <i>B. impatiens</i>, be interpreted carefully as findings may not relate to all bee species.