The unexpected links between declining bumble bee species
Posted onFebruary 1, 2022by|, ,
You’ve seen the headlines “bees are declining!” and have seen the calls to “save the bees”. The media has done a great job at raising awareness that there is a problem, but not so great a job explaining who these headlines are actually about. Many of these slogans are referring to the wellbeing of the European honey bees (Apis mellifera), a single, non-native commercial species brought to North America from Europe many decades ago.
The bees that really need saving are our native bees, the bees that have co-evolved with our native plants over time and are integral in maintaining our local ecosystems. One group of native bees that are particularly at risk are the adorable, fluffy bumble bees (Genus: Bombus).
It is not a commonly known fact, but “bumble bee” does not refer to a single species, but to a whole genus.
There are around 46 different species of bumble bee in North America, with many varying traits that allow them to use different floral resources and landscapes.
The front of WPC’s identification card for the most common bumble bee species in South Central Ontario. This identification card gives an example of the bumble bee diversity in Canada. This ID card can be downloaded here.
There are two bumble bee species that have been recognized by the government via assessments by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), as endangered species: the rusty-patched bumble bee (Bombus affinis) and the gypsy cuckoo bumble bee (Bombus bohemicus).
The “cuckoo” part of the gypsy cuckoo bumble bee name indicates the parasitic strategy of the species; they steal the colony and resources of other bumble bee species, their host. Cuckoo species (subgenus: Psithyrus) do not produce workers of their own, rather they enlist the services of the host colony workers to perform the foraging and house-keeping tasks required. Of the 46 bumble bee species, only 6 are classified as “cuckoos”.
The gypsy cuckoo bumble bee parasitizes the rusty-patched bumble bee in eastern Canada, making these species’ populations linked. Once the rusty-patched bumble bee was one of the most common species in southern Ontario prior to 1980’s – now it has not been observed in Canada since 2009, at Pinery Provincial Park. The last location the gypsy cuckoo bumble bee was also found in Ontario was Pinery Provincial Park, in 2008.
On the left is a rusty-patched bumble bee, eastern host of the gypsy cuckoo bumble bee (Photo: Christy Stewart). The parasitic gypsy cuckoo bumble bee is on the right. (Photo: Nigel Jones)
The gypsy cuckoo is a generalist parasitic bumble bee, meaning it has more than one species that it can use as its host colony. In addition to using the rusty-patched bumble bee as a host in eastern Canada, they also parasitize the western bumble bee (Bombus occidentalis) and the yellow-banded bumble bee (Bombus terricola) in western Canada. Notably, western bumble bee and yellow-banded bumble bee populations are also in decline.
Did you know that there is something else that connects these non-parasitic declining species (Bombus terricola, Bombus affinis, and Bombus bohemicus)? They all belong to the same subgenus, Bombus, which means they are more closely related to each other than to other bumble bee species.
The connection of these species and cause of their declines are a hot topic in bumble bee research.
On the left is a western bumble bee (Photo: Tiffani Harrison), and right, a yellow-banded bumble bee (Photo: Ellen Richard).
Just because the gypsy cuckoo bumble bee is a parasite, does not mean this species should be disliked. On the contrary, they are important to protect as they add diversity and represent a unique relationship between species. Parasitic species are actually great indicators for their host populations – if we observed gypsy cuckoo bumble bee populations increase in Eastern Canada it would likely mean that rusty-patched populations have increased as well!
Every species, even parasites, are important to protect because of their special ecological relationships.