Detection and importance of micro- and macronutrients in pollen collected by bumblebees

Bees decline worldwide, and both scientists and public worry about the observed trends and wonder about their drivers. Many of the discussed culprits are directly or indirectly linked to food resource availability and quality and thus to nutrition. However, while numerous studies found correlations between bee abundance and flowering plant diversity and composition, few explicitly quantified the relationship between plant community (nutritional) composition and the nutritional quality of resources collected by bees, or the subsequent effect on colony fitness. To better understand this relationship, we will investigate the mechanisms underlying pollen foraging choices and nutritional resource intake in bumblebees. Specifically, we want to find out whether bees assess pollen nutritional quality to compose a diet that enables maximal possible colony fitness (i.e. an optimal diet) or whether they follow behavioral rules of thumb (e.g. always mix resources) to minimize the risk of nutritional deficiencies and/or toxic compounds. We hereby expect that, besides the distribution of resources in the environment, relationships between several micro- and macronutrients in pollen determine bee foraging strategies. This is to say, if contents of nutrients (e.g. single amino acids) and/or nutrient groups (e.g. protein, total amino acids) are correlated, bees can infer a maximum of information on pollen nutritional quality from perceiving and assessing one or a few nutritional cues (e.g. a specific amino acid) and thus compose an optimal diet, while the lack of such a relationship would render mixing resources at random the best strategy. To differentiate between the two strategies, we will combine behavioral experiments (i.e. our newly established method of chemotactile proboscis extension conditioning and feeding choice assays) and chemical analyses of plant pollen.We believe that the knowledge obtained from our study will greatly increase our understanding on how alterations in the composition of floral resources available can affect resource foraging and thus nutritional intake and colony health in social bees.