Honey bees preferentially consume freshly-stored pollen

Authors: Carroll, Mark; Goodall, Craig; Brown, Nicholas; DOWNS, ALEXANDRA - University Of Arizona; Sheehan, Timothy; Anderson, Kirk

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2017
Publication Date: 4/21/2017
Citation: Carroll, M.J., Goodall, C.R., Brown, N.J., Downs, A.M., Sheehan, T.H., Anderson, K.E. 2017. Honey bees preferentially consume freshly-stored pollen. PLOS ONE. 12(4). Article e0175933. https://doi.org/10.1371/journal.pone.0175933.
DOI: https://doi.org/10.1371/journal.pone.0175933

Interpretive Summary: Honey bees collect and store pollen in cells in a preserved form known as stored pollen, or beebread. Bees add nectar and honey to collected pollen to form stored pollen. Bees eat stored pollen from a wide selection of pollen cells that have been stored for different lengths of time. We examined the feeding preferences of honey bees for different-aged stored pollens. We monitored the addition and removal of individual pollen cells from 18 brood frames in 6 colonies over 8 days time. Despite a greater number of older pollen cells on the frames, bees preferred to consume freshly-stored pollen cells instead of older pollen cells. Newer pollen cells were eaten more often than expected, while older pollen cells were eaten less often than predicted. Similar preferences were observed in choice tests where caged bees were given a choice between two equal-sized blocks of different-aged pollen cells. Bees consumed 1 day-old pollen three times as much as 10 day-old pollen and two times as much as 5 day-old pollen. These feeding preferences for freshly-stored pollen occurred despite a lack of clear advantages to bee development. Young adult bees reared for a week on 1 day-old, 5 day-old, or 10 day-old pollen cells did not differ in body mass or feeding gland nutrient amounts. Our results do not support a commonly held idea that stored pollen improves in taste or nutritional value with time. Rather, pollen cells that are not eaten in the first few days build up as extra pollen cells on colony frames. Bees’ preferences for fresh stored pollen may be due to leftover odors produced by microbes or the pollen grains before preservation. This study may be used to improve the taste of supplemental feeds to bees.

Technical Abstract: Honey bees (Apis mellifera) collect and store both honey and pollen in preserved forms. Pollen storage involves the addition of honey or nectar and oral secretions to pollen granules. It is controversial whether the duration of pollen storage alters the palatability or nutritive value of the pollen storage medium. We examined how bees utilize different-aged stored pollen during an extended pollen flow. The deposition of pollen into wax cells and subsequent consumption were monitored daily on 18 brood frames from 6 colonies over an 8d observation period. Despite a greater abundance of older stored pollen cells on brood frames, bees showed a marked preference for the consumption of freshly-stored pollen. Two to four day-old pollen cell contents were significantly more likely to be consumed, while pollen cell contents more than seven days old were eaten at much lower rates. Similar experiments that controlled for cell abundance and spatial effects using cage assays yielded the same result. One day-old stored pollen was consumed approximately three times more often than 10d-old stored pollen, and two times more often than 5d-old stored pollen. These consumption preferences for freshly-stored pollen occurred despite a lack of clear developmental advantages. Young adult workers reared for 7 days on 1d-, 5d-, or 10d-old stored pollen showed no difference in body mass, stored pollen consumption, hindgut fecal material accumulation, or hypopharyngeal gland (HPG) protein titers, suggesting that different-aged pollen stores did not vary in their nutritional value to adult bees. These findings are inconsistent with the hypothesis promoting a period of microbially-mediated, “beebread maturation” that results in greater palatability or nutritive value for aged pollen stores. Rather, stored pollen that is not eaten in the first few days accumulates as excess stores preserved in a less preferred, but nutritionally-similar state.