The Problems with the Decline of the Bumble-Bee

Queen Red-Tailed Bumble-Bee, Bombus lapidarius

The decline in bee numbers in Europe over the past 60 years has been a source of concern for a number of reasons. As well as the obvious loss of biodiversity, there is also the problem of a decrease in associated wild plant species and a decrease in the yield of certain crops (1). Bumble bees are no exception to this decline. In Ireland, six of the twenty species recorded are classed as being endangered or vulnerable (2).

Irish Bumble-Bee Species and Their Conservation Status*+

Species	Status
Bombus distinguendus	EN
Bombus ruderarius	VU
Bombus sylvarum	EN
Bombus monticola	LC
Bombus lucorum	LC
Bombus magnus	DD
Bombus cryptarum	DD
Bombus terrestris	LC
Bombus pratorum	LC
Bombus hortorum	LC
Bombus jonellus	LC
Bombus pascuorum	LC
Bombus muscorum	NT
Bombus lapidarius	NT
Bombus barbutellus	EN
Bombus rupertris	EN
Bombus campestris	VU
Bombus bohemicus	NT
Bombus vestalis	NE

One of the possible reasons often cited for this decline is the strict dietary specialisation of certain species (3). Those species who rely on a smaller number of plant species for food should be more threatened. However, this hypothesis is not borne out in the case of the Red-Tailed Bumble Bee (Bombus lapidarius). In Britain, it is a ubiquitous species, yet it has a very narrow floral diet (4), which dismisses the idea that diet alone is the cause of declining bee numbers.

Queen Red-Tailed Bumble-Bee (Bombus lapidarius)

With its red-orange rump and jet black body, B. lapidarius is quite the attractive species. Females can be seen at this time of year looking for burrows under stones in which to build nests (5,6). Unfortunately, B. lapidarius is classed as near treathened in Ireland (2). This decline has come in parallel with a loss of its major habitats here, coastal dunes and unimproved grassland. However as the example above with regards to diet shows, the decline is most likely due to a combination of factors.

*Conservation Status Key: EN=Endangered; VU=Vulnerable; NT=Near Threatened; LC=Least concern; NE=Not evaluated; DD=Data deficient.
+Adapted from Fitzpatrick et al., 2007.

References:

1. Goulson et al., 2008. Annual Review of Entomology 53 pp. 191-208
2. Fitzpatrick et al., 2007. Conservation Biology 21 pp. 1324-1332
3. Goulson et al, 2009. Biodiversity and Conservation 17 pp. 3269-3288
4. Connop et al., 2010.  Biological Conservation 143 pp. 2739-2746
5. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 144
6. Chinery, 1997. Collins Gen Insects p. 250