Abstract
Larvae and imagos of bees rely exclusively on floral rewards as a food source but host-plant range can vary greatly among bee species. While oligolectic species forage on pollen from a single family of host plants, polylectic bees, such as bumblebees, collect pollen from many families of plants. These polylectic species contend with interspecific variability in essential nutrients of their host-plants but we have only a limited understanding of the way in which chemicals and chemical combinations influence bee development and feeding behaviour. In this paper, we investigated five different pollen diets (Calluna vulgaris, Cistus sp., Cytisus scoparius, Salix caprea and Sorbus aucuparia) to determine how their chemical content affected bumblebee colony development and pollen/syrup collection. Three compounds were used to characterise pollen content: polypeptides, amino acids and sterols. Several parameters were used to determine the impact of diet on micro-colonies: (i) Number and weight of larvae (total and mean weight of larvae), (ii) weight of pollen collected, (iii) pollen efficacy (total weight of larvae divided by weight of the pollen collected) and (iv) syrup collection. Our results show that pollen collection is similar regardless of chemical variation in pollen diet while syrup collection is variable. Micro-colonies fed on S. aucuparia and C. scoparius pollen produced larger larvae (i.e. better mates and winter survivors) and fed less on nectar compared to the other diets. Pollen from both of these species contains 24-methylenecholesterol and high concentrations of polypeptides/total amino acids. This pollen nutritional “theme” seems therefore to promote worker reproduction in B. terrestris micro-colonies and could be linked to high fitness for queenright colonies. As workers are able to selectively forage on pollen of high chemical quality, plants may be evolutionarily selected for their pollen content, which might attract and increase the degree of fidelity of generalist pollinators, such as bumblebees.
Highlights
Pollen is one of the prime nutrient resources used for adult and larval development of bees [1,2,3]
Polypeptide contents of C. scoparius, S. caprea and S. aucuparia were quite similar, around 7–8% of lyophilized weight, but were lower for Cistus sp. and C. vulgaris, around 2% of lyophilized weight. These results were corroborated by the total amino acid contents, which were higher in C. scoparius, S. caprea and S. aucuparia than in Cistus sp. and C. vulgaris, around 14% of lyophilized weight (Table 1)
The five diets contained the full spectrum of essential amino acids, one-way ANOVA showed significant difference between the five pollen diets according to their essential amino acid content (F4,11 = 29258, p,0.001)
Summary
Pollen is one of the prime nutrient resources used for adult and larval development of bees [1,2,3]. Interspecific variability in essential nutrients (e.g. proteins, sterols and carbohydrates) may be a constraint for bee development and species permanence at least for polylectic bees that mix pollen resources (i.e. constraint hypothesis developed by [13,14,15]). Assessment of pollen quality based on chemical composition may be a factor driving foraging behaviour in polylectic species [11,20]. The effects of pollen quality on the development and behaviour of polylectic bees remain largely unknown
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