Crithidia mellificae in Osmia cornuta. Crithidia mellificae in Osmia cornuta

The haploid susceptibility hypothesis predicts that male bees should be more susceptible and pathogens from managed honey bees (Apis mellifera) might contribute to the decline of wild bees. However, detection of novel pathogens in wild bees does not necessarily imply that they serve as hosts. Here, we test the haploid susceptibility hypothesis by challenging male and female wild bees (Osmia cornuta) with the honey bee trypanosome Crithidia mellificae.