Examining the effects of pollen macronutrients on bumble bee (Bombus impatiens) queen diapause survival and post-diapause reproductive performance

Pollination of approximately 75% crops worldwide depends on insect pollinators, and a majority of these services are provided by bees. Bumble bees are key pollinators in natural and managed ecosystems, however, like other pollinators, they are experiencing global declines, attributed to the destruction of habitat, loss of floral resources, and changing climatic conditions.

Bumble bees face numerous environmental stressors, but the winter-diapause is a particularly demanding period in their lifecycle. Queens in seasonal environments are dormant for several months and face challenges such as cold-stress and starvation. Finding appropriate and sufficient nutritional resources prior to diapause is critical for both diapause survival and successful colony foundation post-diapause. Gaining knowledge of the optimal nutritional intake in queens during this life stage is critical for devising mechanisms for bumble bee conservation and management.

Here, we asked how artificially manipulated pollen diets varying in their 1) protein and lipid ratio (P:L) and 2) total protein and lipid amounts within a specific ratio, affected queen performance during the solitary stage. We examined how diet affected pre-diapause pollen consumption, mating behavior, mass gain, diapause survival, and post-diapause reproduction. We found that although queens are typically fed with honeybee collected pollen containing 1:1 P:L, their diapause and post-diapause survival were highest when pollen had a nutritional ratio of approximately 4:1 P:L.

Our results demonstrate the importance of high-quality pollen diets for bumble bees, particularly during vulnerable life-stages. These findings provide valuable information for improving the conservation and management of bumble bees.