Interspecific Variation in Bumblebee Performance on Pollen Diet: New Insights for Mitigation Strategies

Abstract

Bumblebees (i.e. Bombus genus) are major pollinators of flowering wild plants and crops. Although many species are currently in decline, a number of them remain stable or are even expanding. One factor potentially driving changes in bumblebee distribution is the suitability of plant communities. Actually, bees probably have specific nutritional requirements that could shape their floral choices and constraint them in the current context of global change. However, most studies primarily focus on one bumblebee species at a time, making comparative studies scarce. Herein we performed comparative bioassays on three bumblebee species (i.e. Bombus hypnorum, B. pratorum and B. terrestris) fed on three different pollen diets with distinct nutritive content (Cistus, Erica and Salix pollen diets). Micro-colony performance was compared through different developmental and resource collection parameters for understanding the impact of change in pollen diet on different bumblebee species. The evidence suggests that B. terrestris is by far the most competitive species because of its performance compared to the other species, regardless of pollen diet. Our results also highlight a Bombus species effect as pollen diet impacts the micro-colonies in different ways according to the actual bumblebee species. Such interspecific variation in Bombus performance in response to a dietetic change underlines the importance of considering different bumblebee species in mitigation strategies. Such comparative studies are good advice for developing appropriate suites of plant species that can benefit threatened species while supporting stable or expanding ones.

Trialling techniques for rearing long-tongued bumblebees under laboratory conditions

“…We found that queens lay eggs readily under artificial conditions even without the use of cocoons as stimuli; this might be further improved using CO 2 exposure (Röseler 1985;Tasei 1994). It is also clear that species responded differently to captive conditions, as previously shown in other bumblebee species (Bučánková and Ptáček 2012;Ptáček et al 2015;Moerman et al 2016). Repeated egg/larvae abandonment remains a problem.…”

“…Future trials should test methods to manage queen stress from the initial collection through to colony initiation. Trialling various nest box types and pollen diets will further clarify their nesting preferences (Lhomme et al 2013;Moerman et al 2016). Since queens may respond positively to stress-inducing stimuli due to a perceived competitive pressure, techniques to restrict stressful conditions to the first egglaying phase might elucidate this.…”

“…A small number of studies have succeeded in rearing bumblebee species other than B. terrestris or B. impatiens in captivity. Lhomme et al (2013) provided the first precise protocol for rearing two cuckoo species, B. vestalis and B. sylvestris and Moerman et al (2016) showed differential responses to pollen diet between B. terrestris , Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13592-019-00707-7) contains supplementary material, which is available to authorized users. B. pratorum and B. hypnorum micro-colonies reared in captivity.…”

“…Rearing conditions, such as nest box design and pollen type, have a substantial effect on the health and reproductive success of bumblebees reared in captivity. There is some evidence to show that giving young, long-tongued colonies access to flowers allows natural foraging and improves colony development (Lhomme et al 2013;Ptáček et al 2015;Moerman et al 2016). Many of the long-tonged bumblebees can be characterised as pocket makers, feeding their larvae a solid rather than liquid diet (Den Boer and Duchateau 2006).…”

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

“…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].…”