The Cuckoo Gypsy Bumble Bee: A Species Endangered

B. bohemicus male Image: Magne Flåten via wikimedia.org CC BY-SA 3.0 (B. bohemicus female here)

By Zach DeLong

When people hear of endangered species they often think of large and impressive creatures like the Siberian Tiger or Panda Bear, but we often forget about the smaller, yet no less impressive species that need our help as well. The charmingly named Cuckoo Gypsy Bumblebee, or as scientists all it Bombus bohemicus, is a member of the family Apidae, in the order Hymenoptera. Though the Species at Risk Act (SARA) currently has no status for the Cuckoo Gypsy Bumblebee, it has been recognized and listed as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The term “endangered” is a hot topic, but there may be confusion about what it truly means.  As defined by COSEWIC, an endangered species is “a wildlife species facing imminent extirpation or extinction[1]”. In the case of the Cuckoo Gypsy Bumblebee, this means the species is at risk of disappearing from the Canadian wilderness.

The Cuckoo Gypsy Bumblebee is an inquiline parasite of other types of bees, which means the Cuckoo Gypsy Bumblebee is a home invader. Normally such an invader would be attacked by the workers within the hive, but the Cuckoo Gypsy Bumblebee produces a variety of chemicals which both disguise it as a member of the host species[2] and inhibit worker aggression towards the invader[3]. The Cuckoo Gypsy Bumblebee is a generalist parasite and is surprisingly able to successfully invade a number of different Canadian species, namely the Rusty-patched Bumblebee, the Yellow-banded Bumblebee, and the Western Bumblebee[4]. Once inside the nest the Cuckoo Gypsy Bumblebee engages in a number of dominance behaviours to usurp the host queen, including ejecting host larvae from cells, eating host eggs and even outright attacking the host queen[5]. Coexistence with the host queen is preferable as her suppressor pheromones help control the workers who might otherwise attempt to become reproductively active themselves, so the invading Cuckoo Gypsy queen will often choose to shove or perform faux-stinging behaviour over outright killing her co-matriarch[5]. The Cuckoo Gypsy queen produces no workers of her own.  This means she relies on host workers to defend the nest, rear her young, and forage for food[2]. Instead, all her offspring are reproductive with a 1:1 female to male ratio[6]. Young Gypsy Cuckoo Bumblebees can be seen flying about and feeding on flowers while they wait for their reproductive organs to mature so they can begin looking for a mate and a suitable host nest to invade.

Distribution of Cuckoo Gypsy Bumble Bee throughout North America. Image: COSEWIC

The Cuckoo Gypsy Bumblebee is widely distributed across a wide range in Canada, with individuals found in all provinces and territories except Nunavut[4], though populations are mostly concentrated in southern portions of Ontario and Quebec, and the Maritime provinces. Its decline across Canada has been attributed to a number of factors. It has been shown that a certain host density must be maintained for cuckoo bee parasites to be able to persist in a given area, and the general decline of bees throughout Canada has subsequently damaged Cuckoo Gypsy Bumblebee populations[4]. The mass spraying of crops with pesticides, particularly neonicotinoids, and the release of pathogen-carrying exotic bee species have impacted both cuckoo bees and host densities across Canada[4]. If we want the Cuckoo Gypsy Bumblebee to recover, perhaps the best way is to make Canada a more bee friendly environment as a whole. If we address issues resulting in the decline of other bee species, we can provide the population density necessary to facilitate persistent cuckoo populations. Additionally, addressing factors such as pesticide usage and the introduction of foreign pathogens would have positive effect on Cuckoo Gypsy Bumblebees as this would not only increase the population density of hosts, but also improve survival rates of Cuckoo Gypsy Bumblebees themselves.

References

[1]Assessment Process, Categories and Guidelines. COSEWIC. 2005-06-15. 2015-07-08. http://www.cosewic.gc.ca/eng/sct0/assessment_process_e.cfm#tbl5

[2]Kirsten Kreuter, Elfi Bunk, Anna Lückemeyer, Robert Twele, Wittko Francke, Manfred Ayasse(2012). How the social parasitic bumblebee Bombus bohemicus sneaks into power of reproduction. Behavioral Ecology and sociobiology, Vol 66, Issue 3, pp 475-486.

[3]Stephen J. Martin, Jonathan M. Carruthers, Paul H. Williams, Falko P. Drijfhout(2010). Host Specific Social Parasites (Psithyrus) Indicate Chemical Recognition System in Bumblebees. Journal of Chemical Ecology, Vol 36, Issue 8, pp 855-863.

[4]COSEWIC Wildlife Species Search: Bumble Bee, Gypsy Cuckoo | Bombus bohemicus. COSEWIC. 2002-10-21. 2011-11-07. http://www.cosewic.gc.ca/eng/sct1/searchdetail_e.cfm?id=1232&StartRow=191&boxStatus=All&boxTaxonomic=All&location=1&change=All&board=All&commonName=&scienceName=&returnFlag=0&Page=20

[5]R. M. Fisher(1988). Observations on the behaviours of three European cuckoo bumble bee species (Psithyrus). Insectes Sociaux, Volume 35, Issue 4, pp 341-354.

[6]Vergara, Carlos H. (2003). Suppression of ovarian development of Bombus terrestris workers by B. terrestris queens, Psithyrus vestalis and Psithyrus bohemicus females. Apidologie 34, pp 563–568

This post is also available in: Français