Connecting the nutrient composition of seasonal pollens with changing nutritional needs of honey bee (Apis mellifera L.) colonies

Authors: DeGrandi-Hoffman, Gloria; Gage, Stephanie; Corby-Harris, Vanessa; Carroll, Mark; Chambers, Mona; Graham, Richard; Watkins De Jong, Emily; Calle, Samantha; Meador, Charlotte; Snyder, Lucy; Ziolkowski, Nicholas

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2018
Publication Date: 7/11/2018
Citation: Hoffman, G.D., Gage, S.L., Corby-Harris, V.L., Carroll, M.J., Chambers, M.L., Graham, R.H., Watkins De Jong, E.E., Calle, S.N., Meador, C.A., Snyder, L.A., Ziolkowski, N.F. 2018. Connecting the nutrient composition of seasonal pollens with changing nutritional needs of honey bee (Apis mellifera L.) colonies. Journal of Insect Physiology. 109:114-124. https://doi.org/10.1016/j.jinsphys.2018.07.002.
DOI: https://doi.org/10.1016/j.jinsphys.2018.07.002

Interpretive Summary: Honey bee colonies have a yearly life cycle, and nutritional requirements might differ between brood rearing and colony expansion in the spring and population contraction and preparation for overwintering in the fall. We analyzed polyfloral mixes of spring and fall pollens to determine if the nutrient composition differed with season. Next, we fed both types of seasonal pollens to bees reared in spring and fall. We compared the development of brood food glands (i.e., hypopharyngeal glands - HPG), and the expression of genes in the fat body between bees fed pollen from the same (in-season) or different season (out-of-season) when they were reared. Because pathogen challenges often heighten the effects of nutritional stress, we infected a subset of bees with Nosema to determine if bees responded differently to the infection depending on the seasonal pollen they consumed. We found that spring and fall pollens were similar in total protein and lipid concentrations, but spring pollens had higher concentrations of amino and fatty acids that support HPG growth and brood production. Bees responded differently when fed in vs. out of season pollen. The HPG of both uninfected and Nosema-infected spring bees were larger when they were fed spring (in-season) compared to fall pollen. Pollen type also affected gene expression and physiology in spring bees. More than 200 genes were differentially expressed in spring bees depending on the seasonal pollens they consumed. When infected with Nosema, approximately 400 genes in spring bees showed different expression patterns depending on the pollen type. Fall bee responses to pollen type and Nosema infection differed from spring bees. In fall bees, HPG size was not affected by pollen type, though HPG were smaller in bees infected with Nosema. Very few genes were differentially expressed with pollen type in uninfected (4 genes) and infected bees (5 genes). In fall bees, pollen type did not affect patterns of infection-induced expression. Our data suggest that physiological responses to seasonal pollens differ between bees reared in the spring and fall with spring bees being significantly more sensitive to pollen type especially when infected with Nosema. This study provides evidence that seasonal pollens may provide levels of nutrients that align with the activities of honey bees during their yearly colony cycle. The findings are important for the planning and establishment of forage plantings to sustain honey bees, and in the development of seasonal nutritional supplements fed to colonies when pollen is unavailable.

Technical Abstract: Free-ranging herbivores have yearly life cycles that generate dynamic resource needs. Honey bee colonies also have a yearly life cycle, and nutritional requirements might differ between times of brood rearing and colony expansion in the spring and population contraction and preparation for overwintering in the fall. We analyzed polyfloral mixes of spring and fall pollens to determine if the nutrient composition differed with season. Next, we fed both types of seasonal pollens to bees reared in spring and fall. We compared the development of brood food glands (i.e., hypopharyngeal glands - HPG), and the expression of genes in the fat body between bees fed pollen from the same (in-season) or different season (out-of-season) when they were reared. Because pathogen challenges often heighten the effects of nutritional stress, we infected a subset of bees with Nosema to determine if bees responded differently to the infection depending on the seasonal pollen they consumed. We found that spring and fall pollens were similar in total protein and lipid concentrations, but spring pollens had higher concentrations of amino and fatty acids that support HPG growth and brood production. Bees responded differently when fed in vs. out of season pollen. The HPG of both uninfected and Nosema-infected spring bees were larger when they were fed spring (in-season) compared to fall pollen. Spring bees differentially regulated more than 200 genes when fed in- vs. out-of-season pollen. When infected with Nosema, approximately 400 genes showed different infection-induced expression patterns in spring bees depending on pollen type. In contrast, HPG size in fall bees was not affected by pollen type, though HPG were smaller in those infected with Nosema. Very few genes were differentially expressed with pollen type in uninfected (4 genes) and infected fall bees (5 genes). Pollen type did not affect patterns of infection-induced expression in fall bees. Our data suggest that physiological responses to seasonal pollens differ between bees reared in the spring and fall with spring bees being significantly more sensitive to pollen type especially when infected with Nosema. This study provides evidence that seasonal pollens may provide levels of nutrients that align with the activities of honey bees during their yearly colony cycle. The findings are important for the planning and establishment of forage plantings to sustain honey bees, and in the development of seasonal nutritional supplements fed to colonies when pollen is unavailable.