Where is the Buzz?

Part 1. Habitat Loss

Wild pollinators of the Bombus species (a.k.a. bumblebees) are social insects with major importance to ecosystems and food production through the pollination of wild flowers and crops. It is estimated that 78% of wild flowering plants rely on insect pollination¹, and the presence of wild pollinators greatly enhances crop yield compared to commercial pollinators alone². Through the provision of pollination services, insect pollinators contribute to 1/3 of our food crop production, contributing €153 billion to the global economy each year. It’s safe to say, we highly benefit from these busy little insects.

Insect pollination contributes to up to 33% of world wide food crop production. (Source)

With this in mind, it’s quite alarming that bee decline in both abundance and diversity has been reported around the world (Europe, Asia, USA)^3,4, and Ireland is no exception. Of the 20 bumblebee species in Ireland, The National Biodiversity Centre field data indicates 14% decline in Irish bumblebees in the last six years.

So, who or what is to blame? Unfortunately, there isn’t any one answer. Rather, it’s thought that a number of factors all acting against our wild pollinators at the right (or wrong) time has led to a decline in bee abundance and species diversity we see today. In this blog series, we will cover various factors of bee decline including (but not limited to) habitat loss, pesticide use and disease.

Habitat Loss

With the introduction of modern and intensified agriculture³ and the urbanization of land⁵, bees face extreme challenges in finding the ideal habitat. Intensified agriculture strips the preferred flowers (food) for bumblebees and lowers the diversity of flowering plants available to bees, leading to poor nutrition. Different bumblebee species prefer different nesting sites and different plant types depending on the time of year⁶. Since the 20^th century, there has been a 97% loss of flower-rich land in the UK⁷ leading to the decline of many long-tongued bee species³.

Along with decreased nesting sites and poor floral diversity, agriculture often introduces bumblebees to a high density of commercial bee species, and therefore competition for floral resources and nesting sites¹¹. With increased commercial bee species, spatial changes are observed in wild bumblebee species and shifts between plant species.

Bumblebee foraging on the common garden wild flower Taraxacum vulgaria (dandelion) (source).

However, our gardens can help! Sub-urban land can support a high diversity of wild bee species by providing floral diversity and nesting sites^8,9! Studies conducted in the UK identified the importance of sub-urban gardens for bumblebee nesting sites, with fence lines and hedgerows also supporting an abundance of bumblebees⁹. However, herbicides can act as a limit to some preferred food sources¹⁰. Emerging queens rely on all the floral resources they can get to establish colonies and thrive in areas with lots of wild flowers. Often seen as weeds, wild flowers such as dandelions and knapweeds provide good quality nectar and pollen for bees. So, forget about the weed killer and lawnmower for now, and enjoy how easy it is the support our wild pollinators.

** Stay tuned for part 2 of our bumblebee decline series and make sure to follow our twitter (@CarolanLab) to be informed of our next blog post!

References

1. Ollerton, J., Winfree, R. and Tarrant, S. (2011). How many flowering plants are pollinated by animals? Oikos, 120(3), pp.321–326. doi: 10.1111/j.1600-0706.2010.18644.x
2. Garibaldi, L.A., Steffan-Dewenter, I., Winfree, R., Aizen, M.A., Bommarco, R., Cunningham, S.A., Kremen, C., Carvalheiro, L.G., Harder, L.D., Afik, O., Bartomeus, I., Benjamin, F., Boreux, V., Cariveau, D., Chacoff, N.P., Dudenhöffer, J.H., Freitas, B.M., Ghazoul, J., Greenleaf, S., Hipólito, J., Holzschuh, A., Howlett, B., Isaacs, R., Javorek, S.K., Kennedy, C.M., Krewenka, K.M., Krishnan, S., Mandelik, Y., Mayfield, M.M., Motzke, I., Munyuli, T., Nault, B.A., Otieno, M., Petersen, J., Pisanty, G., Potts, S.G., Rader, R., Ricketts, T.H., Rundlöf, M., Seymour, C.L., Schüepp, C., Szentgyörgyi, H., Taki, H., Tscharntke, T., Vergara, C.H., Viana, B.F., Wanger, T.C., Westphal, C., Williams, N. and Klein, A.M. (2013). Wild Pollinators Enhance Fruit Set of Crops Regardless of Honey Bee Abundance. Science, 339(6127), pp.1608–1611. doi: 10.1126/science.1230200
3. Goulson, D., Lye, G.C. and Darvill, B. (2008). Decline and conservation of bumble bees. Annual Review of Entomology, 53(1), pp.191–208. doi: 10.1146/annurev.ento.53.103106.093454
4. Williams, P., Tang, Y., Yao, J. and Cameron, S. (2009). The bumblebees of Sichuan (Hymenoptera: Apidae, Bombini). Systematics and Biodiversity, 7(2), pp.101–189. doi: 10.1017/S1477200008002843
5. Bates, A.J., Sadler, J.P., Fairbrass, A.J., Falk, S.J., Hale, J.D. and Matthews, T.J. (2011). Changing bee and hoverfly pollinator assemblages along an urban-rural gradient. PLoS ONE, 6(8). doi: 10.1371/journal.pone.0023459
6. Goulson, D., Nicholls, E., Botías, C., Rotheray, E.L., Botias, C. and Rotheray, E.L (2015). Bee declines driven by combined stress from parasites, pesticides, and lack of flowers. Science (New York, N.Y.), 347(6229), p.1255957. doi: 10.1126/science.1255957
7. Howard, D.C., Watkins, J.W., Clarke, R.T., Barnett, C.L. and Stark, G.J. (2003). Estimating the extent and change in Broad Habitats in Great Britain. Journal of Environmental Management, 67(3), pp.219–227. doi: 10.1016/S0301-4797(02)00175-5
8. Baldock, K.C.R., Goddard, M.A., Hicks, D.M., Kunin, W.E., Mitschunas, N., Osgathorpe, L.M., Potts, S.G., Robertson, K.M., Scott, A. V., Stone, G.N., Vaughan, I.P. and Memmott, J. (2015). Where is the UK’s pollinator biodiversity? The importance of urban areas for flower-visiting insects. Proceedings. Biological sciences / The Royal Society, 282(1803), p.20142849. doi: 10.1098/rspb.2014.2849
9. Osborne, J.L., Martin, A.P., Shortall, C.R., Todd, A.D., Goulson, D., Knight, M.E., Hale, R.J. and Sanderson, R.A. (2008). Quantifying and comparing bumblebee nest densities in gardens and countryside habitats. Journal of Applied Ecology, 45(3), pp.784–792. doi: 10.1111/j.1365-2664.2007.01359.x
10. Muratet, A. and Fontaine, B. (2015). Contrasting impacts of pesticides on butterflies and bumblebees in private gardens in France. Biological Conservation, 182, pp.148–154. doi: 10.1016/j.biocon.2014.11.045
11. Velthuis, H. H., & Van Doorn, A. (2006). A century of advances in bumblebee domestication and the economic and environmental aspects of its commercialization for pollination. Apidologie, 37(4), 421-451.