Bombus pensylvanicus


Species Decline and Conservation

           In many parts of the United States, the Bombus Pensylvanicus was considered the most common bumble bee until 1990 (Nature Serve 2012). Since then there has been a great decline in the numbers of not only the Bombus pensylvanicus, but also many other North American bumble bee species (Cameron et al. 2011). The current Rounded Global Status rank for B. pensylvanicus is G3—indicating that the species is vulnerable (Nature Serve 2012). There is no evidence to suggest whether the species will continue to decline or stabilize in the coming decades (Nature Serve 2012). The American Bumble Bee is an important pollinator so the decline of this species can have other ecological impacts (Lozier and Cameron 2009). While there is speculation as to the cause of the decline of Bombus pensylvanicus, there is not yet any conclusive evidence explaining the downward trend (Nature Serve 2012).

            There are however, a myriad of possible causes. One of the most probable explanations has to do with landscape modification; many natural B. pensylvanicus habitats which previously hosted the plants pollinated by this species have been destroyed to allow the mass production of crops such as corn and soybeans (Lozier and Cameron 2009). It is also suggested that B. pensylvanicus’ aboveground nests are more vulnerable to destruction than underground nests of other Bombus species (Lozier and Cameron 2009). A threat to the Bombus pensylvanicus, but known for the decline of bumble bee populations in Europe is the pathogen Nosema bombi (Cameron et al. 2011). Though there is no conclusive evidence linking this parasite to the decline of Bumble Bees in the United States, it is a possible explanation because the decline of North American Bumble Bees mirrors that of the decline in Europe starting in the 1950’s (Cameron et al. 2011). Another possible explanation for the decline is the use of pesticides on commercial crops; these pesticides—meant to control crop-destroying pests NOT pollinators like Bombus pensylvanicus—have been found in concentrations lethal to the American Bumble Bee on guttation drops on grass and other plants (Encyclopedia of Life).

            The extinction of pollinator species such as the American Bumble Bee would be devastating to ecosystems, but we would also be losing a piece of our history. So what can be done to preserve the Bombus pensylvanicus? In the discussion of their analysis of historical Bumble Bee DNA, Lozier and Cameron suggest planting wildflower seeds in the areas surrounding commercial crops, in lieu of mowing these areas down (Lozier and Cameron 2009). They say that this could increase not only pollination opportunities and habitat resources, but also increase gene flow between populations of Bombus species.

The NatureServe Explorer website provides a detailed explanation of the American Bumble Bee's current species status: