Hive‐stored pollen of honey bees: many lines of evidence are consistent with pollen preservation, not nutrient conversion

Abstract

Honey bee hives are filled with stored pollen, honey, plant resins and wax, all antimicrobial to differing degrees. Stored pollen is the nutritionally rich currency used for colony growth and consists of 40–50% simple sugars. Many studies speculate that prior to consumption by bees, stored pollen undergoes long-term nutrient conversion, becoming more nutritious ‘bee bread’ as microbes predigest the pollen. We quantified both structural and functional aspects associated with this hypothesis using behavioural assays, bacterial plate counts, microscopy and 454 amplicon sequencing of the 16S rRNA gene from both newly collected and hive-stored pollen. We found that bees preferentially consume fresh pollen stored for <3 days. Newly collected pollen contained few bacteria, values which decreased significantly as pollen were stored >96 h. The estimated microbe to pollen grain surface area ratio was 1:1 000 000 indicating a negligible effect of microbial metabolism on hive-stored pollen. Consistent with these findings, hive-stored pollen grains did not appear compromised according to microscopy. Based on year round 454 amplicon sequencing, bacterial communities of newly collected and hive-stored pollen did not differ, indicating the lack of an emergent microbial community co-evolved to digest stored pollen. In accord with previous culturing and 16S cloning, acid resistant and osmotolerant bacteria like Lactobacillus kunkeei were found in greatest abundance in stored pollen, consistent with the harsh character of this microenvironment. We conclude that stored pollen is not evolved for microbially mediated nutrient conversion, but is a preservative environment due primarily to added honey, nectar, bee secretions and properties of pollen itself.

Fatty Acids and Proximate Composition of Beebread

“…There is a limited number of studies in the literature regarding the nutritional properties att ributed to the stored pollen. The reported results are contradictory, indicating either no signifi cant change or marginally increased nutrition (2). Bee pollen collection is a fairly new development.…”

Honey bee gut microbial communities are robust to the fungicide Pristine® consumed in pollen

“…We fed the bees polyfloral mixes of pollen that were collected during the year when the experiment was conducted, so the species composition probably differed. There is evidence that bee bread communities (Anderson et al 2014) and midgut/pyloric (Ludvigsen et al 2015) bacterial communities fluctuate with pollen source and season. Gut bacterial communities also can differ among colonies (Hroncova et al 2015).…”

“…In the second experiment, we observed a large number of non-core bacteria, particularly P. apium , non-Firm 4 and Firm 5 Lactobacillus sp., Enterococcaceae , and the pathogen P. larvae . P. apium is found at lower levels in the gut (Corby-Harris et al 2014a;Martinson et al 2011;Martinson et al 2012;Moran et al 2012;Sabree et al 2012) and is typically more abundant in hive food stores (Anderson et al 2014), queens (Kapheim et al 2015;Tarpy et al 2015), larvae (Vojvodic et al 2013), and in the hypopharyngeal glands and crops of nurses (Corby-Harris et al 2014b). Because P. apium is relatively abundant in food stores, hypopharyngeal glands, and crop, one possibility is that the guts displaying high P. apium titers were recently inoculated through either pollen feeding or trophallaxis.…”

Honey bee colonies provided with natural forage have lower pathogen loads and higher overwinter survival than those fed protein supplements

“…Possible reasons include the activity of proteolytic enzymes added to pollen during storage and metabolism by microbes in stored pollen (Gilliam et al 1989;Metges 2000). However, a recent study suggests that bacteria in stored pollen contribute to its preservation rather than predigestion or nutrient conversion (Anderson et al 2014). Though the reasons for nutritional differences between pollen and beebread are not clear, both should be included in nutritional analyses of a pollen source ( rapini pollen Figure 6.…”