Some bee-pollinated plants provide nutritionally incomplete pollen amino acid resources to their pollinators

Abstract

For pollinators such as bees, nectar mainly provides carbohydrates and pollen provides proteins, amino acids, and lipids to cover their nutritional needs. Here, to examine differences in pollinator resources, we compared the amino acid profiles and total amino acid contents of pollen from 32 common entomophilous plants in seven families. Our results showed that the amino acid profiles and contents in pollen samples differed according to the plant family and the chromatography method used, i.e., high-performance liquid chromatography (HPLC) versus ion exchange chromatography (IEX). Pollen from Boraginaceae species had the highest total amino acid contents (361.2–504 μg/mg) whereas pollen from the Malvaceae family had the lowest total amino acid contents (136–243.1 μg/mg). Calculating an amino acid score (AAS) that reflects pollen nutritional quality showed that slightly less than half of the species (19 out of 32) had the maximum nutritional score (AAS = 1) and offered high nutritional quality pollen amino acids for bee pollinators. Though they had high total amino acid contents, the amino acid composition of the studied Boraginaceae species and several members of the Fabaceae was not optimal, as their pollen was deficient in some essential amino acids, resulting in suboptimal amino acid scores (AAS < 0.7). Except for cysteine, the measured amino acid contents were higher using IEX chromatography than using HPLC. IEX chromatography is more robust and is to be preferred over HPLC in future amino acid analyses. Moreover, our observations show that some bee-pollinated species fail to provide complete amino acid resources for their pollinators. Although the implications for pollinator behavior remain to be studied, these deficiencies may force pollinators to forage from different species to obtain all nutritionial requirements.

A novel farmland wildflower seed mix attracts a greater abundance and richness of pollinating insects than standard mixes

“…resulted in failure to lay eggs in B. terrestris micro‐colonies; while Austin and Gilbert (2021) found Osmia bicornis larvae survival was positively correlated with carbohydrate quantity. Therefore, bee species benefit from a diverse diet in which pollen and nectar are sourced from a variety of plant species in order to obtain all essential amino acids and sufficient quantities of sugar nectar (Hanley et al, 2008; Jeannerod et al, 2022; Vaudo et al, 2015). Although our novel WB mix was found to attract the greatest abundance of insect pollinators, we did not record if visits were made for pollen or nectar foraging/collection.…”

“…showed the Fabaceae mix was statistically no better than a fallow plot for attracting bumblebees (though see Cole et al, 2022 The nutritional components of pollen and nectar varies widely between plant species and families (Hanley et al, 2008;Jeannerod et al, 2022), which can in turn limit the growth and survival of bee broods. Brunner et al (2014) found that a diet consisting of just Taraxacum spp.…”

“…Additionally, all foragers recorded were adult forages, therefore it is unclear if they were foraging for their own consumption, or collecting to provide for offspring. As the protein and carbohydrate contents of food can have a big effect on the reproductive success, this should be considered when forming a wildflower seed mix (Jeannerod et al, 2022).…”

“…Different flower species produce pollen and nectar of varying nutritional components, qualities, and quantities. The main nutritional component of nectar is carbohydrate in varying quantities (Hicks et al, 2016), while pollen is a source of protein and lipids (Jeannerod et al, 2022). Insects such as bees must not only consume sufficient quantities of food to meet their own energy expenditure requirements, but must also obtain an adequate and diverse range of nutrients to feed their larvae.…”

Social but not solitary bee abundance tracks pollen protein accumulation in forest canopy gaps

“…Although nectar sugar content was not measured, larger floral display area is often correlated to nectar sugar content (Guezen & Forrest, 2021), suggesting that bees were attracted to visual traits that signal nectar quality rather than pollen protein concentration. In addition, the relative composition of amino acids in pollen can vary substantially among flowering plants (Jeannerod et al, 2022; Nepi et al, 2012), though the consequences of this variation for bee foraging are not yet entirely clear. In honeybees ( Apis mellifera L.) foraging is linked with the proportion of essential amino acids (valine, leucine and isoleucine) in pollen and can drive preferences for certain plant species (Cook et al, 2003), but wild bee nutritional networks are reported to exhibit little specialisation for specific amino acids (Kriesell et al, 2017).…”