Wild species 2010: chapter 15

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Insects: Bumblebees

Bombus - The genus of insects which includes the social and cuckoo bumblebees. These are winged pollinating insects which feed entirely from the pollen and nectar of flowers. Bumblebees are large, hairy and often brightly coloured.

Quick facts

• There are about 250 species of bumblebees in the world; 41 occur in Canada.
• When excluding species ranked as Extinct, Extirpated, Undetermined, Not Assessed, Exotic or Accidental, the majority (94%) of bumblebees in Canada have Canada General Status Ranks (Canada ranks) of Secure, while 6% have Canada ranks of May Be At Risk. However, it should be noted that most of the bumblebee species were ranked as Undetermined.
• Much of the range of bumblebees occurs in under-surveyed regions of the country. No bumblebees have Canada ranks of At Risk, because COSEWIC has not yet assessed any bee species, although the Rusty-patched Bumblebee (Bombus affinis) and Western Bumblebee (Bombus occidentalis) are currently being considered.
• Bumblebees have various adaptations to colder climates, making them excellent pollinators in adverse weather conditions. This includes a rare physiological capability to thermo regulate to achieve body temperatures well above ambient temperatures.
• The queen bee is the largest bee in the colony, followed by the workers (females) and drones (males).
• Bumblebees will not die if they use their stings, whereas honey bees do. Male bees do not possess stings.

Background

The genus Bombus (bumblebees) includes approximately 250 species found primarily in temperate regions of North America, Central America, South America, Europe and Asia. Bumblebees require three different habitats for nesting, overwintering, and foraging. Generally, nests can be underground in abandoned rodent burrows or above ground in trees or under grass mounds. Overwintering sites for mated queens consists of burrows in loose soil, sand, decomposing vegetation (including mulch) and rotting logs just a few inches below the surface. In some species, young queens overwinter at the same sites as their maternal nests. Foraging habitat can be anything from forest, meadow, urban gardens, bogs, agricultural fields, etc. Good foraging habitat has many suitable flowers which provide nectar and pollen sources throughout the spring, summer and fall. The common and easily recognized bumblebees are large, furry and corbiculate (i.e. with pollen baskets) bees.

Bumblebees are eusocial (i.e. colonial with a queen and worker castes, where the workers are the offspring of the queen). The colonies are annual; mated queens emerge from hibernation in the spring after overwintering and begin feeding. These queens search for a suitable nest site where they then begin their colonies. A few weeks after the queen’s initial egg-laying, female workers emerge and begin foraging for the colony and feeding the brood. As the summer progresses, the colony reaches maximum worker production and begins producing males and potential queens. These reproductive individuals leave the nest and mate with bees from other nests. After mating, young queens enter diapause and overwinter. The males and the rest of the colony decline as fall approaches until they all die come frost. The timing of queen emergence and the length of the colony cycle differs widely by species. Bumblebees belonging to the subgenus Psithyrus are an exception as they do not produce a worker caste, but are social parasites (cuckoo bumblebees). Instead females usurp colonies of other species and propagate using the host species resources.

Bumblebees are extremely important pollinators for agriculture both in the field and in greenhouses. Unlike honeybees, they are able to forage under cold, rainy and cloudy conditions. This makes them excellent pollinators for a variety of crops in temperate regions such as tomatoes, berries, peppers, beans, etc. They are also extremely important pollinators for native flowering plants which provide food and shelter for native mammals and birds.

We have evidence in North America that some of our bumblebee species are going undergoing rapid decline. In fact, one species known from Oregon and California (Franklin’s Bumblebee) has recently been listed by the International Union for Conservation of Nature (IUCN) as Critically Endangered. Currently, the suspected threats to wild bumblebees are habitat loss, urbanization and pollution, pesticide use, introduction of disease from managed bees and climate change.

Bumblebees are fascinating insects which have been studied by amateurs in gardens for centuries. They have also been the subject of many scientific studies in ecology and physiology. They are large, fuzzy and colourful. Although the females possess a sting, they are docile animals and can be observed busily flying from flower to flower. Bumblebees are extremely important pollinators of native flowering plants and agricultural crops, and are thus critical to the sustainability of ecosystems and their loss could impact many other species, including ourselves.

Status of knowledge in Canada

Bumblebees are relatively easy to identify in the field, are active during the day and are ubiquitous in many habitats with flowering plants. Their specific life history traits and habitat requirements are well known compared to most insects. However, little is known about their distribution. The specimens in museums and collections throughout Canada provide baseline data which we can analyze to determine population trends over time.

Bumblebees have been used as model organisms in Canada for many decades. In the 1970s and 1980s in particular, bumblebees were used to perform many experiments investigating community and evolutionary ecology. With the onset of Colony Collapse Disorder among managed honey bees, the importance of native pollinators has recently become an important issue. Bumblebees are the best known native bees and many projects are currently geared towards their conservation.

Because bumblebees are insects that live in colonies and many individuals are not reproductive, well designed long-term monitoring is critical to understanding the status of these species in the wild. Also, studies of bumblebee diseases and parasites are important to fully understand how the growing managed bumblebee sector is affecting wild populations. Further studies to better understand life history traits such as mating behaviour and overwintering requirements will help with the design of species-specific conservation plans.

Richness and diversity in Canada

Within Canada, bumblebee species richness is highest in regions of British Columbia, Alberta and the Yukon, where up to 34 of the 41 species have been reported (figure 15). Especially important bumblebee habitats are located in the alpine meadow regions of the country. Also with high species richness are southern parts of Saskatchewan, Manitoba, Ontario and Quebec. While all the species of Canadian bumblebees are found in other countries (i.e. mainly the USA, though some are holarctic), most of the native habitat for the majority of species is located in Canada.

Species spotlight - Rusty-patched Bumblebee

At the first signs of spring, Rusty-patched Bumblebee (Bombus affinis) queens can be found foraging on whatever plants they can find. Early sources of pollen such as willows and coltsfoot are crucial to the survival of this early-emerging species. Once the queen replenishes nutrients lost over the winter, she begins looking for abandoned rodent burrows to establish a nest. She lays eggs and forages to feed herself and the developing larvae until the first brood of workers hatch. The workers then take over all house-keeping and foraging duties and the queen focuses all her energy on producing eggs and building up the colony size. Towards the fall, the queen starts laying eggs which become males and young queens. These reproductive individuals go out and reproduce before the mated queens settle down for a long winter. Compared to other native bumblebee species, the Rusty-patched Bumblebee has one of the longest colony cycles, emerging as early as mid-March and continuing on until late October. As a result, they have cumulatively one of the largest colony sizes of all the other species and have relatively large body sizes to deal with the cool spring and fall weather.

As recently as 30 years ago, the Rusty-patched Bumblebee was one of the most common bees in meadows, urban areas, forests, and wetlands. In the past 10 years, less than five individuals have been spotted throughout its native range of southern Ontario and Quebec, despite intensive searches. Most recently, this species has been found only in Pinery Provincial Park, on the eastern shores of Lake Huron. As a result, this important pollinator is currently being considered for listing by COSEWIC under the Species at Risk Act and has been given the General Status Canada rank of May Be At Risk. Because of the species’ distinctive rusty patch on the second stripe of its abdomen and its long colony cycle, it is a great species for the general public and avid gardeners to keep an eye out for.

Species spotlight - Common Eastern Bumblebee

The Common Eastern Bumblebee (Bombus impatiens) is a frequent flower visitor, spotted by many Canadian gardeners. It is distinctive as the only bumblebee with a single yellow stripe at the top of its abdomen (the rest of the abdomen is completely black). While the Common Eastern Bumblebee has always been quite common, in recent decades it has expanded its range eastward into Nova Scotia and increased in abundance in some places of its original range. For this reason it was given the General Status Canada rank of Secure. There are many natural history characteristics that make this bumblebee successful in today’s changing landscapes. Firstly, it has adopted man-made objects as good nesting material. In urban areas, its colonies can frequently be found under decks, between cinder blocks, and sometimes even on apartment balconies! Common Eastern Bumblebees have a medium tongue length, meaning they can forage from hundreds of plant species, including native, introduced and crop plants. Queens also produce very large colonies of variable size workers, depending on the quality of available food.

The adaptability of this species to be successful in a variety of conditions has made it the perfect species for managed pollination of many food crops, in fields and in greenhouses. It is an especially good pollinator for tomatoes and sweet peppers, which require buzz pollination (honey bees are incapable of this behaviour). An unfortunate result of the domestication of this species for crop pollination may be that the Common Eastern Bumblebee becomes common in western Canada. Numerous commercial rearing companies are shipping this species all over North America for pollination of a variety of crops and in recent years, it has been spotted in the wild in British Columbia. Although this species is native to Canada, it poses a serious threat to the diverse bumblebee fauna of western Canada. Its success throughout its native range indicates it could prove to be quite the competitor for food and nest sites, potentially impacting other native bumblebee species.

Results of general status assessment

The majority of Canada’s 41 bumblebess have Canada ranks of Undetermined (25 species, 61%, figure 15 and table 22). Fifteen species have Canada ranks of Secure (37%) and one species (2%) have a Canada rank of May Be At Risk.

Threats to Canadian bumblebees

Bumblebees require suitable habitat for the entire length of their colony cycle, as they only produce reproductive individuals at the end of the summer. This means that the entire colony needs good sources of nectar and pollen from a variety of flowers throughout the spring, summer and fall. Because they bring back food materials to the nest, bumblebees are highly susceptible to cumulative effects of pollution and pesticides (especially neonicotinoids) in their foraging habitats. They are also negatively impacted by climate change, invasive species which may compete for food plants (e.g. the Honey Bee (Apis mellifera)), and introduced disease from managed bumblebees used in greenhouse and crop pollination. Loss of food plants due to human land use practices, and invasive plant species also reduces habitat suitability for many bee species, including bumblebees.

Conclusion

This general status assessment shows that the majority (61%) of bumblebee species in Canada have a Canada rank of Undetermined. This is the result of a lack of survey work in most parts of the country. However some species have been well researched and have shown drastic and alarming declines in as little as 30 years. Accordingly, with ongoing survey work, it is possible that more species may be assigned a general status rank of May Be At Risk (currently 2%) or Sensitive.

While North American bumblebees are ubiquitous in historical collections, amateur naturalists and field biologists have only recently become interested in these creatures. Within the next few years, new identification keys and public awareness will likely result in a better understanding of this group of important pollinating insects.

Further information

Benton, T. Bumblebees. Collins publishing, London, UK.

BugGuide, Genus Bombus. (Accessed April 9, 2010).

Discover life bumblebee key. (Accessed April 9, 2010).

Kearns, C. A. and Thomson, J. D. 2001. The natural history of bumblebees: a sourcebook for investigations. University Press of Colorado, Boulder: 130 pp.

Paul William’s colour key to the Bombus of the World. (Accessed April 9, 2010).

References

Colla, S. R. and Packer, L. 2008. Evidence for decline in eastern North American bumblebees (Hymenoptera: Apidae), with special focus on Bombus affinis Cresson. Biodiversity and Conservation 17: 1379-1391.

Heinrich, B. 1979. Bumblebee economics. Harvard University Press, Cambridge: 245 pp.

Laverty, T. M. and Harder, L. D. 1988. The bumblebees of eastern Canada. Canadian Entomologist 120: 965-987.

Thorp, R. W. and Shepherd, M. D. 2005. Profile: subgenus Bombus. In Red list of pollinator insects of North America (M. D.

Shepherd, D. M. Vaughan and S. H. Black, editors). The Xerces Society for Invertebrate Conservation, Portland.

Williams, P. H. and Osborne, J. L. 2009. Bumblebee vulnerability and conservation world-wide. Apidologie 40: 367-387.