Timing and size of the daily pollen meals eaten by adult females of a solitary bee (Nomia melanderi)(Apiformes: Halictidae)

Authors: Cane, James; DOBSON, HEIDI - Whitman College; BOYER, BRENDAN - Whitman College

Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2016
Publication Date: 5/3/2016
Citation: Cane, J.H., Dobson, H.E., Boyer, B. 2016. Timing and size of the daily pollen meals eaten by adult females of a solitary bee (Nomia melanderi)(Apiformes: Halictidae). Apidologie. 48(1):17-30.

Interpretive Summary: Pollen plus energy-rich nectar, or secretions made from them, constitute the diets of bees. For more than a century, we have known that bee larvae feed on prodigious quantities of pollen, as do young “nurse” honey bees. Conversely, the dietary needs of adult solitary bees are poorly known, although their daily nutritional demands include 1-2 huge eggs and, for many ground-nesting species, a secreted waterproofing lipid for nest cells. We studied hourly, daily and lifetime patterns of pollen consumption by ground-nesting females of the alkali bee, Nomia melanderi, an important managed pollinator of alfalfa. Adult females ate pollen soon after they emerged, and daily thereafter for the next two weeks. Nesting females consistently gorged on pollen during their last flight before nightfall. Females always start the morning empty, sometimes consuming pollen during the day too. Usually, though, their crops were swelled with clear nectar used to moisten the growing larval provision mass. Several implications emerge from our study. First, pollen available at flowers should not be exhausted before dusk. Otherwise, the females’ reproduction will be curtailed. On farms, this means not over-stocking bees for pollination. In addition, females will need some bloom for feeding before starting to nest. Because mother bees are eating pollen daily, they will be exposed first to any toxins on or in pollen, days before their eggs hatch. They also have the opportunity to compare tastes and satiation from particular pollen meals, possibly self-selecting for pollen pollens as their foraging season progresses.

Technical Abstract: Solitary bees daily provision nest cells with pollen and nectar for their progeny, but little is known of their own eating habits for self-maintenance. The alimentary canals of nesting female alkali bees (Nomia melanderi) were dissected daily at different hours and days throughout their nesting lives, beginning on the day of emergence. By daily marking new nests, the ages of resident females were known. Few bees taken at their nests in the morning had eaten pollen, but females were increasingly likely to eat pollen over the afternoon. Every evening, every dissected female’s crop contained pollen. A full pollen meal comprises the pollen taken from 34 or so tripped alfalfa flowers, obtainable in about 4 minutes of foraging when virgin flowers are plentiful. However, if bee numbers exceed floral carrying capacities, the floral resources can be exhausted by evening. As a consequence, nesting females may not be able to replenish the pollen proteins and fats likely needed to mature subsequent eggs. Because females eat pollen daily, they are exposed to any toxins present with those pollen meals. When nesting females eat pollen, they also could be digestively evaluating pollen nutrient quality, enabling the selection of superior pollens with which to provision later nest cells.