Bombus fervidus

This species occurs across a large range in Canada and the United States as well as parts of Mexico. It is unlikely that one threat explains the long-term decline trends observed. Regional studies give us some information about possible threats to this species. Gillespie (2010) found B. fervidus and B. pensylvanicus to be among the most uncommon species in Massachusetts but with significantly higher levels of Nosema bombi (but not other parasites) compared to the common species. Nosema bombi is known to spillover from managed bumblebees (Colla et al. 2006) and may be implicated in declines.

Open grassland habitats, old fields, and tallgrass habitats are likely the most suitable habitat types for this species in its range. This habitat type is of conservation concern and exists only in small remnants. In a survey performed in Iowa, Hines and Hendrix (2005) found higher abundance and diversity of bumblebees in high quality tallgrass prairie sites, depending on quality of the surrounding landscape. Landscape quality was assessed as the diversity and abundance of floral resources at various radii from the survey site. High quality sites with higher bumblebee diversity also contained B. fervidus, indicating this species may be more susceptible to environmental stressors, such as habitat loss (Hines and Hendrix 2005). Bumblebee diversity was found to be best predicted by high floral resource availability in surrounding grasslands (Hines and Hendrix 2005).

Agricultural intensification leads to loss of this habitat type. Pesticide use can also impact this species occurring on or near agriculture. Limited to above ground nesting in natural grasslands or agricultural fields, this species is susceptible to habitat loss or direct exposure to pesticides. In some cases, farmers may kill bumblebee colonies when they nest above ground (frequent among many species of the subgenus Thoracobombus) because they impact cattle and other domestic livestock. The long-tongue of this species restricts its foraging to certain flower types (e.g. legumes). Conversion in agricultural farmland from the use of nitrogen-fixing legumes to artificial fertilizers may further decrease available forage.

A meta-analysis across bumblebee faunas in three continents found species with late emergence (like B. fervidus) are more vulnerable to stressors (Williams et al. 2009). Natural wildfires and prescribed burning may benefit bees by creating open forage in otherwise unsuitable habitat. As such, the suppression of natural fires can result in habitat loss for bees and other grassland species, particularly in forested regions. In light of this, prescribed burning is frequently used as a conservation management tool to restore natural ecosystems (e.g. grasslands), increase biodiversity (particularly plant species), and control invasive species (e.g. Brockway et al. 2002, Hatch et al. 2002). However, depending on fire intensity, duration, season, frequency, and patchiness, prescribed fire may result in population loss for pollinators, particularly at sites where few individuals of a species exist (e.g. Swengel 1996). As such, both fire suppression and fire itself may threaten this species in some areas.

Reduced genetic diversity resulting from any of these threats can be particularly concerning for bumblebees, since their method of sex-determination can be disrupted by inbreeding, and since genetic diversity already tends to be low in this group due to the colonial life cycle (i.e. large numbers of bumble bees found locally may represent only one or a few queens) (Goulson 2010, Hatfield et al. 2012, but see Cameron et al. 2011 and Lozier et al. 2011).      

Conservation Needs: 

• Restoration, creation and preservation of natural grassland habitats.
• Restriction of harmful pesticide use on or near suitable habitat.
• Promotion of farming practices that increase the abundance of nitrogen-fixing fallow (legumes).
• Protection of species from diseases introduced by managed bees.