Pollen nutrients better explain bumblebee colony development than pollen diversity

Abstract

Bumblebees are valuable pollinators of numerous wild and cultivated plants. They can forage on variable pollen resources. As some pollen species lack particular nutrients or have global low nutritional quality, it has been suggested that bumblebees mix their pollen incomes to ensure a global balanced diet. The hypothesis that a mixed pollen diet better supports bumblebee colony development than a single pollen diet has been poorly explored. We compared the impact of mono‐, di‐ and trifloral diets on microcolony development of Bombus terrestris using three pollen resources with different nutrient contents (Cytisus scoparius, Erica sp. and Sorbus aucuparia) as well as their mixes. Nine parameters (e.g. pollen efficacy: total weight of larvae/total weight of pollen collection) were used to compare the microcolony performances. Moreover, we measured the influence of the pollen diversity and nutritional composition on relevant parameters. We showed that microcolonies can potentially better develop on mixed pollen diets, but single pollen diet can also be as good as mixed pollen diet. Moreover, the sterol concentration appeared as a key factor to establish the impact of a pollen diet on the bumblebee colony development. This study reveals that diverse pollen diet does not necessary equate with good colony development and supports the importance of selecting floral resources by considering their nutrient contents for bee conservation management.

Floral Species Richness Correlates with Changes in the Nutritional Quality of Larval Diets in a Stingless Bee

“…Similar field studies on the effect of landscape on colony reproductive output also found a strong effect of resource abundance but no clear effect of resource nutritional quality [9,34]. However, several studies conducted in the laboratory showed a positive correlation between increasing pollen diversity in diets as well as resource nutrient (e.g., pollen protein) content and bee health [11][12][13][14][15]. Our studies further suggest that T. carbonaria, like other social bee species, for example, bumblebees [9,34], can compose larval provisions of sufficient quality to sustain proper larval development even in environments with low plant species richness, or that they have a relatively high tolerance for variation in the nutritional quality of larval provisions.…”

“…The floral composition of collected pollen (and likely also nectar) is strongly affected by the composition of plant communities available in the surrounding environment [9,10]. It directly affects the health, performance and fitness of bee colonies, with health and fitness often increasing with pollen floral diversity [11][12][13][14][15] and depending on floral composition [15].…”

Effects of neonicotinoid insecticide exposure and monofloral diet on nest-founding bumblebee queens

“…Queens in each of the three pesticide treatment groups also received one of three unique pollen diet treatments: primarily Erica (heather) or Cistus (rockrose) pollen ( purchased fresh from Pollenergie and stored at 2808C), or a polyfloral mixture (50% each by weight) of the two pollens. Previous studies have found that microcolonies subsisting solely on Cistus and Erica pollens have reduced larval weights and colony development rates versus when provided with some other pollen species [30,46,47,52]. These effects may be due to the relatively low protein contents of these pollens (e.g.…”

“…An additional stressor that bumblebees face is declining floral resource abundance and diversity, which is being driven by land use change (including a trend towards monocultural practices), phenological mismatches between bee flight and plant flowering periods, and other global changes (reviewed in [41,42]). Bumblebees are largely floral generalists that collect pollen from a wide variety of plant species [43], and a breadth of recent studies suggest that a lack of diversity in their pollen diet, or relying solely on pollen from particular plant species, can have negative effects on egg production and larval development in small groups of queenless workers (termed 'microcolonies') [30,[44][45][46][47][48]. Recent studies have also found additive, negative effects of neonicotinoid exposure and monofloral pollen diet on microcolony growth [23].…”

Best be(e) on low fat: linking nutrient perception, regulation and fitness

“…Moreover, the nutritional quality of pollen and in particular its protein content seems to largely determine bumblebee colony development (K€ amper et al 2016;Moerman et al 2017;Roger et al 2017) as well as bumblebee immune defence (Di Pasquale et al 2013;Brunner et al 2014;Roger et al 2017). Pollen protein content and amino acid profiles furthermore correlate with foraging preferences (Kitaoka & Nieh 2009;Leonhardt & Bl€ uthgen 2012;Kriesell et al 2017).…”