Honey bee (Apis mellifera L.) foraging rewards in sunflowers: effect of floral traits on visitation and variation in pollen quality over two consecutive years

Authors: FERGUSON, MARY BETH - Former ARS Employee; Prasifka, Jarrad; Carroll, Mark; Corby-Harris, Vanessa; DeGrandi-Hoffman, Gloria

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2024
Publication Date: 6/7/2024
Citation: Ferguson, M., Prasifka, J.R., Carroll, M.J., Corby-Harris, V.L., Hoffman, G.D. 2024. Honey bee (Apis mellifera L.) foraging rewards in sunflowers: effect of floral traits on visitation and variation in pollen quality over two consecutive years. Journal of Apicultural Research. https://doi.org/10.1080/00218839.2024.2364948.
DOI: https://doi.org/10.1080/00218839.2024.2364948

Interpretive Summary: Honey bees and other wild bees are needed to pollinate the sunflower crop. Wild bees that specialize on sunflowers prefer types that have shallow flowers, a feature that makes their nectar easier for bees to drink. Because it was not clear whether honey bees show the same strong preference for sunflowers with shallow flowers (or other nectar-related traits), tests were conducted on honey bee preference over two years. In one of two years, honey bees showed a strong preference for shallow flowers. In the other year, low nectar levels may have concealed bee preferences. Collections from various sunflower types showed differences in the nutritional value of pollen, the primary dietary source of protein and fats for bees. Because sunflowers are grown across many different regions of the United States (and the world) differences in temperature, humidity or other conditions might change the attractiveness or nutritional value of sunflower nectar and pollen.

Technical Abstract: Sunflower production depends on pollination by honey bees, Apis mellifera L., and wild bees. For wild sunflower oligoleges, preference for various sunflower lines seems to reflect the quantity (or accessibility) of floral rewards, with floret size (˜ accessibility of sunflower nectar) appearing most important. However, it is less clear how honey bees, a key generalist, are affected by sunflower floral traits. The honey bee-sunflower interaction was explored to test if accessibility of nectar (˜ floret size) and related floral traits explain foraging preferences, and to assess potential nutritional variation in sunflower pollen. In the first of two years, honey bee foraging preference increased with decreasing floret length similar to previous observations with wild pollinators. In the second year, no similar response was seen, though nectar rewards (by volume or volume × concentration) were remarkably low compared to the previous year. Pollen collected from bagged plants in the second year showed sunflower lines differed in concentrations (µg/mg ± SE) of total fatty acids and essential fatty acids. In general, it appears that honey bee responses to floral traits are similar to those of wild bees responsible for pollinating much of the sunflower crop in the central United States and that variation in nutritional quality of sunflower pollen is greater than previously known. Because of the broad geographic distribution on the sunflower crop, additional research on how the environment influences floral rewards and sunflower-pollinator interactions may be needed.