Bumble Bee Breeding on Artificial Pollen Substitutes

Abstract

Bumble bees are important pollinators for many temperate crops. Because of the growing demand for food from entomophilous crops, bumble bee colonies are commercially reared and placed in fields or greenhouses to guarantee sufficient pollination services. Besides, commercial colonies are increasingly used in laboratories for various bioassays under controlled conditions. For both usages, bumble bee colonies are commonly provided with sugar solution and honey bee-collected pollen pellets. However, the latter display several disadvantages since they may contain pollutants, pathogens, or toxic phytochemicals. Consequently, companies have developed pollen-free artificial diets to sustain colonies. Such diets are designed to boost worker health in the field, in complement of floral pollen collected by workers outside the colonies, but their suitability in ‘closed’ systems without access to floral pollen, such as in laboratory bioassays, is arguable. Here, we used microcolonies of the commercially important bumble bee Bombus terrestris L. (Hymenoptera: Apidae) to assess the suitability of five artificial pollen substitutes and three mixed diets. We also assessed the evaporation rate of the different diets as it could impact their suitability. At the end of the bioassays, microcolonies fed the artificial diets showed a reduced offspring development when compared to microcolonies fed natural pollen, which was partly offset by mixing these diets with natural pollen. By contrast, the artificial diets did not have deleterious effects on worker’s health. We discuss the potential nutritional and physical causes of artificial diets unsuitability for offspring development and encourage further research to accordingly establish appropriate pollen-free diets for bumble bee breeding.

Comparative analysis of 3 pollen sterilization methods for feeding bumble bees

“…Thus, production of colonies in North America alone requires over 21,000 kg of honey bee-collected pollen annually. So far, artificial diets have not provided sufficient protein for bumble bee colony development and require supplementation with pollen (Bortolotti et al 2020, Gekière et al 2022). Restricting pollen to bumble bee colonies can lead to negative impacts on colony health and growth, creating a great need for honey bee-collected pollen in production (Rothman et al 2019, Rowe et al 2023).…”

Pollen as Bee Medicine: Is Prevention Better than Cure?

“…However, it should be interpreted with caution, as it partly contrasts with the study of Palmer-Young et al [ 47 ] who showed that C. bombi cells developing in vitro resistance towards the phytochemical eugenol did not have a higher infectiousness than naïve parasite cells in eugenol-fed bumble bees. Regarding fat body content, although it is commonly used as a proxy for individual immunocompetence e.g., [ 31 , 34 , 38 , 48 ], underlying mechanisms remain poorly understood, making difficult clear interpretations of any effect. In prophylactic treatments, poppy pollen led to slightly higher fat body content than sunflower and multifloral pollen, whereas heather pollen led to reduced fat body content when compared to any other diet in therapeutic treatments.…”

“…One way to overcome this limitation would be to rely on a diet shift rather than on a starvation–feeding transition, by providing bumble bee microcolonies with a specialized metabolite-free and nutritionally well-balanced diet prior to feeding them with pollen candidates [ 39 ]. However, hitherto, researchers have failed to develop a specialized metabolite-free artificial diet which supports bumble bee colony growth [ 48 , 68 ]. Moreover, even such an artificial diet could lead to experimental limitation as central metabolites (i.e., carbohydrates, proteins and lipids) play pivotal roles in host–parasite interactions (e.g., see [ 69 ] for the importance of sugars for in vitro Crithidia bombi growth).…”

Heather pollen is not necessarily a healthy diet for bumble bees

“…Queenless microcolonies of five workers were exposed to specific diet treatments (Fig. 1): control pollen (i.e., willow pollen is used because of unsuitability of artificial pollen for bumblebee development; Gekière et al, 2022b) containing either (i) parasitised or (ii) non-parasitised bumble bees; heather pollen containing either (iii) parasitised or (iv) non-parasitised bumble bees; microcolonies fed with willow pollen supplemented with extracts of flavonoids from heather pollen containing either (v) parasitised or (vi) non-parasitised bumble bees. Diets (i) and (ii) were used as controls as well as to assess the parasite impacts.…”