Abstract
Dietary macro-nutrients (i.e., carbohydrates, protein, and fat) are important for bee larval development and, thus, colony health and fitness. To which extent different diets (varying in macro-nutrient composition) affect adult bees and whether they can thrive on nectar as the sole amino acid source has, however, been little investigated. We investigated how diets varying in protein concentration and overall nutrient composition affected consumption, longevity, and breeding behavior of the buff-tailed bumble bee, Bombus terrestris (Hymenoptera: Apidae). Queenless micro-colonies were fed either natural nutrient sources (pollen), nearly pure protein (i.e., the milk protein casein), or sucrose solutions with low and with high essential amino acid content in concentrations as can be found in nectar. We observed micro-colonies for 110 days. We found that longevity was highest for pure pollen and lowest for pure sucrose solution and sucrose solution supplemented with amino acids in concentrations as found in the nectar of several plant species. Adding higher concentrations of amino acids to sucrose solution did only slightly increase longevity compared to sucrose alone. Consequently, sucrose solution with the applied concentrations and proportions of amino acids or other protein sources (e.g., casein) alone did not meet the nutritional needs of healthy adult bumble bees. In fact, longevity was highest and reproduction only successful in micro-colonies fed pollen. These results indicate that, in addition to carbohydrates and protein, adult bumble bees, like larvae, need further nutrients (e.g., lipids and micro-nutrients) for their well-being. An appropriate nutritional composition seemed to be best provided by floral pollen, suggesting that pollen is an essential dietary component not only for larvae but also for adult bees.
Highlights
An insect’s stress tolerance and survival depend, among other things, on the amount and ratio of particular nutrients consumed [1,2,3,4]
Amino acid amounts used for the low concentration mixture were the average concentrations found for essential amino acids and proline in floral nectar of eight bee-pollinated
Individual overall food consumption differed significantly between different diets (ANOVA: F = 10.64, p < 0.001, significance level after Bonferroni: α = 0.0125, Figure 1A)
Summary
An insect’s stress tolerance and survival depend, among other things, on the amount and ratio of particular nutrients consumed [1,2,3,4]. Food source quality and availability play a major role in insect survival, as they directly determine the nutritional composition of the diets [5,6]. The diet of bees is usually comprised of nectar and pollen [7,8]. Nectar is considered the main food source of adult bees [12]. In turn, is predominantly consumed by larvae and represents the primary source of protein and fat [7,13,14].
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