Mycelium as a beneficial dietary additive to support managed bumble bee development and colony growth

Managed bumble bee (Hymenoptera: Apidae: Bombus impatiens (Cresson, 1863)) colonies are commercially reared and sold for crop pollination. The rearing process requires feeding honey bee (Hymenoptera: Apidae: Apis mellifera (Linnaeus, 1758))-collected multifloral pollen mixes to developing bumble bee colonies. Honey bees and bumble bees, however, preferentially forage on pollens with different nutritional profiles to meet different nutritional needs. Therefore, developing supplements to increase palatability and nutrition in pollen diets for these managed bumble bee colonies may better meet their needs. Oyster mushroom (Pleurotus spp.) mycelium is an abundant, renewable, and nutritional resource, making it a promising candidate for such supplements. We evaluated the influences of oyster mushroom mycelium-augmented pollen on bumble bee development and colony growth. We hypothesized that: (i) microcolonies provided with mycelium-augmented pollen produce more offspring; and (ii) mycelium-augmented pollen provides a nutritional benefit to developing bumble bee larvae by increasing their fat content, weight, and body size. We established Bombus impatiens microcolonies and provided them with pollen provisions containing a 1% concentration of two species of oyster mushroom mycelium (Pleurotus columbinus (Agaricales: Pleurotaceae: Pleurotus ostreatus var. columbinus (Quél, 1886), or Pleurotus djamor (Agaricales: Pleurotaceae: Pleurotus djamor (Fries, 1821))) or a mycelium-free control. Microcolonies given P. columbinus-augmented pollen had more offspring with faster development times that were higher in weight and fat content than P. djamor and mycelium-free colonies. This suggests that P. columbinus mycelium has the potential to be a beneficial dietary additive to managed B. impatiens diets to increase colony success and offspring development.