Cause for Concern
Value of Bumblebees
Of the thousands of bees native to North America, bumblebees (Bombus) are among the most recognizable and best known. Over 40 bumblebee species occur in the continental United States alone. Bumblebees are considered particularly effective native pollinators due to their generalist floral preferences, large body size, cold tolerance, and ability to buzz pollinate.
Several hundred native flowering plant species are visited and pollinated by bumblebees, an act that serves to maintain native biodiversity. Bumblebees also also make substantial contributions to agriculture and have proven to be effective pollinators of such crops as blueberries, cranberries, cucumbers, peppers, pumpkins, and watermelons.
With the exception of a few species, bumblebees are eusocial with individual queens establishing annual colonies during spring and early summer. Once established, queens never leave their nests and rely upon their daughter workers to forage for food, care for developing larvae, and defend against predators. Colonies store relatively small food reserves, requiring a near continuous supply of nectar and pollen from flowers over many months to support and complete colony development.
A substantial body of evidence now suggests that the bumblebee faunas of several continents have experienced some degree of decline. Reductions in bumblebee diversity were first reported in the United Kingdom where three species are now extinct and another eight have receded from previously occupied regions. A total of 18 bumblebee species are considered threatened across their ranges in central and western Europe.
Range reductions for some North American bumblebee species have been reported, but only recently have researchers provided quantitative evidence of decline on this continent. In southern Ontario, researchers from York University documented declines in relative abundance for seven bumblebee species over a 35 year time period. Along with those localized declines, the researchers also assessed the persistence of a single species, Bombus affinis, across its historic distribution in eastern North America. Their results indicated that B. affinis was absent from most previously documented sites and that the species had likely been extirpated from a large portion of its range. In the midwestern United States, University of Illinois researchers examined the status of bumblebees in that state and identified the local extirpation of four bumblebee species along with range reductions for an additional four species. On a larger geographic scale, University of Illinois researchers also assessed the occurrence of eight species across their historic ranges in the United States, identifying distributional reductions for four of the targeted species.
A principle driver of bumblebee decline in Europe has been the loss of natural and semi-natural grasslands to agriculture. Grassland communities often represent optimal habitat for bumblebees as they typically support diverse assemblages of flowering plants (nectar and pollen) and relatively abundant nest sites. Intensive agriculture has taken a toll on grasslands across North America as well and been identified as a contributing factor to bumblebee decline in Illinois. Other potential contributors to North American bumblebee declines include pathogen spillover from commercial bumblebee colonies into wild populations, pesticide use, and competition with the non-native European honeybee (Apis mellifera).
Given their economic and ecological values, faunal assessments are currently needed to gain a better understanding of the group’s conservation status (Goulson et al., 2008). The bumblebee fauna of Texas has gone virtually unstudied but merits examination given documented declines across North America. A good starting point is simply determining whether species still inhabit areas of historic occurrence.
Essential starting points for learning more about global bumblebee declines are websites of the leading researchers, specifically:
- Dave Goulson, University of Stirling, United Kingdom
- Paul Williams, The Natural History Museum, United Kingdom
Both worker’s websites provide online access to their many peer-reviewed publications on bumblebee conservation and ecology. Good introductory articles are:
- Goulson, D., G.C. Lye, and B. Darvill. 2008. Decline and conservation of bumblebees. Annual Review of Entomology 53: 191-208.
- Williams P.H. and J.L. Osborne. 2009. Bumblebee vulnerability and conservation world-wide. Apidologie 40: 367-387.
On this continent, Sydney Cameron and her current and former graduate students at the University of Illinois have led the way on assessing the status of bumblebees in the United States. Sheila Colla at York University provided the first quantitative evidence of bumblebee decline in North America and has produced several publications on bumblebee decline. Important works from Cameron and Colla include:
- Colla, S.R., F. Gadallah, L. Richardson, D. Wagner, and L. Gall. 2012. Assessing declines of North American bumble bees (Bombus spp.) using museum specimens. Biodiversity and Conservation 21: 3585-3595.
- Colla, S.R. and L. Packer. 2008. Evidence for decline in eastern North American bumblebees (Hymenoptera:Apidae), with special focus on Bombus affinis. Biodiversity and Conservation 17: 1379-1391.
- Grixti, J.C., L.T. Wong, S.A. Cameron, and C. Favret. 2009. Decline of bumble bees (Bombus) in the North American Midwest. Biological Conservation 142:75–84.
- Cameron, S.A., J.D. Lozior, J.P. Strange, J.B. Koch, N. Cordes, L.F. Solter, and T.L. Griswold. 2011. Patterns of widespread decline in North American bumble bees. Proceedings of the National Academy of Sciences 108:662-667.
- Colla, S. R., M. C. Otterstatter, R. J. Gegear, and J. D. Thomson. 2006. Plight of the bumble bee: pathogen spillover from commercial to wild populations. Biological Conservation 129:461-467.
- Kosior, A., W. Celary, P. Olejniczak, J. Fijal, W. Król, W. Solarz, and P. Plonka. 2007. The decline of the bumble bees and cuckoo bees (Hymenoptera: Apidae: Bombini) of western and central Europe. Oryx 41:79-88.
- Martins, A. C. and G. A. R. Melo. 2010. Has the bumblebee Bombus bellicosus gone extinct in the northern portion of its distribution range in Brazil? Journal of Insect Conservation 14:207-210.
- Otterstatter M. C. and J. D. Thomson. 2008. Does pathogen spillover from commercially reared bumble bees threaten wild pollinators? PLoS One 3(7): e2771.doi:10.1371/journal.pone.0002771.
- Thomson D. M. 2006. Competitive interactions between the invasive European honey bee and native bumble bees. Ecology 85:458–70.
- Williams P. H. 1982. The distribution and decline of British bumble bees (Bombus Latr.). Journal of Apicultural Research 21:236-245.