The importance of time and place: Nutrient composition and utilization of seasonal pollens by European honey bees (Apis mellifera L.

Authors: DeGrandi-Hoffman, Gloria; Corby-Harris, Vanessa; Carroll, Mark; TOTH, AMY - Iowa State University; GAGE, STEPHANIE - Georgia Institute Of Technology; Watkins De Jong, Emily; Graham, Richard; Chambers, Mona; MEADOR, CHARLOTTE - University Of Arizona; OBERNESSER, BETHANY - University Of Arizona

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2021
Publication Date: 3/10/2021
Citation: Hoffman, G.D., Corby-Harris, V.L., Carroll, M.J., Toth, A., Gage, S., Watkins De Jong, E.E., Graham, R.H., Chambers, M.L., Meador, C., Obernesser, B. 2021. The importance of time and place: Nutrient composition and utilization of seasonal pollens by European honey bees (Apis mellifera L.). Insects. 12(3). Article 235. https://doi.org/10.3390/insects12030235.
DOI: https://doi.org/10.3390/insects12030235

Interpretive Summary: Honey bee colonies have a yearly cycle that is supported nutritionally by the seasonal progression of flowering plants. In the spring, colonies grow by rearing brood, but in the fall brood rearing declines in preparation for overwintering. Depending on where colonies are located, the yearly cycle can differ especially in overwintering activities. In temperate climates, colonies reduce or end brood rearing in the fall while in warmer climates; bees can rear brood and forage throughout the year. We tested a hypothesis that nutrients available in seasonal pollens differ based on geographic region, and align with the seasonal activities of colonies. We collected and analyzed spring and fall pollen from regions where brood rearing either stops in the fall or continues through the winter. We fed the pollens to worker offspring of queens that emerged and open mated in each environment (Iowa or California). We measured pollen consumption and sizes of hypopharyngeal (i.e., brood food) glands (HPG) to see if bees responded differently to pollens from the same (local) or different (non-local) region from where the queens originated. We found differences between the nutrient composition of spring and fall pollens from the same region and between regions during the same season. However, bees did not consume more or have larger HPG with local vs. non-local pollens. We did detect differences however, between the queen types and if bees consumed spring vs. fall pollen. Responses to spring pollen aligned with factors supporting brood rearing such as bees having larger HPG. In the fall, bees consumed more pollen and protein, but had HPG that were similar in size (Iowa bees) or smaller (California bees) than in the spring. Our study indicated that to optimize brood rearing, bees should be fed spring pollen, and that fall pollens while consumed at higher rates than spring, may be mostly stored rather than used to rear brood.

Technical Abstract: Honey bee colonies have a yearly cycle that is supported nutritionally by the seasonal progression of flowering plants. In the spring, colonies grow by rearing brood, but in the fall brood rearing declines in preparation for overwintering. Depending on where colonies are located, the yearly cycle can differ especially in overwintering activities. In temperate climates, colonies reduce or end brood rearing in the fall while in warmer climates bees can rear brood and forage throughout the year. To test the hypothesis that nutrients available in seasonal pollens differ based on geographic region, and align with the seasonal activities of colonies, we collected and analyzed pollen in the spring and fall from regions where brood rearing either stops (Iowa) in the fall or continues through the winter (Arizona). We fed both types of pollen to worker offspring of queens that emerged and open mated in each environment. We measured physiological responses to test whether they differed depending on if the pollen was collected from a similar (local) or different (non-local) environment than where the queens were sourced. Specifically, we measured pollen and protein consumption, gene expression levels (hex 70, hex 110, and vg) and hypopharyngeal gland (HPG) development. We found differences in macronutrient content and amino and fatty acids between spring and fall pollens from the same region and differences in nutrient content between regions during the same season. However, bees did not consume more pollen from their region of origin or provide evidence of being locally adapted in their responses (increased physiological metrics) to consuming local pollen. We did detect queen type and seasonal effects in HPG size and difference in gene expression between bees consuming spring vs. fall pollen with larger HPG and higher gene expression levels in those consuming spring pollen. The effects might have emerged from the seasonal differences in nutritional content of the pollens and genetic factors associated with the queen lines we used.