The American bumble bee (Bombus pensylvanicus), is so named because it occurs throughout North America, from Quebec south to Florida and into Mexico. The American bumble bee is a generalist feeder that forages on plants in the milkweed (Asclepiadaceae), composite (Asteraceae), forget-me-not (Boraginaceae), honey-suckle (Caprifoliaceae), morning-glory (Convolvulaceae), legume (Fabaceae), mint (Lamiaceae), blazing star (Primulaceae), rose (Rosaceae), snapdragon (Scrophulariaceae), and nightshade (Solanaceae) families.

Global Range: (200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)) From what is known, the range of this species has not contracted greatly, although it has become rarer. Its pre-1998 range was from Quebec across southern Ontario west to South Dakota and throughout Nebraska and south to southern Florida, and (B. pensylvanicus sonorus) into the mountains of central Mexico. During the 1990s and early 2000s, Schmidt and Jocobson (2005) found populations of B. p. sonorus in each of five southern Arizona mountain ranges they studied. They indicated its presence in the nearby deserts, but not in the more contiguous mountains of northern Arizona. The range of that taxon seems to be from western Texas to southern California and well into Mexico. It is confined to mountains, generally above 1500 meters, in arid regions. The range of B. p. pensylvanicus includes nearly all of the eastern U.S. and apparently most of Texas, as well as the foothills and shortgrass prairies just east of the Rockies. In the Midwest, its northern limit is in the southern parts of Minnesota, Wisconsin, and Michigan.

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

American bumble bee queens are between 21 and 25.5 mm long while workers and drones are smaller, between 14 and 19 mm and 16 and 22 mm, respectively. The queen's head is entirely black with a few gray hairs. The thorax is yellow towards the head and black towards the abdomen; the abdomen is yellow and black. Workers resemble the queen. A drone has a grayish-white face, a black head with some gray, and a thorax with similar coloration to the queen. On a drone, the first part of the abdomen is yellow, and the rest is variable.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Comments: Adults are generalized nectar and pllen gathers. See Di Trani De La Hoz (2006) for a very good autecological study of subspecies sonorus. Super and Moyer's account would be applicable for most of the USA.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: > 300

Unknown

Ants and many bees and wasps are eusocial - meaning they are socially highly organized. Eusocial insects are reproductively specialized, with a reproductive division of labor often involving sterile members caring for the reproductive members. Other defining features of eusociality are overlapping of generations and cooperative care of the young. All ants are eusocial with morphologically different workers and queens. Some bee and wasp species, including honey bees ( Apis mellifera ), carpenter bees ( Xylocopa spp.), bumble bees ( Bombus spp.), paper wasps ( Polistes spp.), and yellowjackets ( Vespula spp.) also exhibit eusociality.

Interestingly, humans are also defined as eusocial.

These bees are eusocial and have an annual nest. In spring, a queen emerges from hibernation in search of a new nest. Worker bees then develop, followed by drones and new queens towards the end of summer. Drones tend to wait around the entrance to hives for the queens to emerge, competing with each other for access. Mated queens hibernate over winter, while workers, drones, and old queens die towards the end of the summer after living about 14 to 25 weeks.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 3
Species With Barcodes: 1

Rounded Global Status Rank: G3 - Vulnerable

Reasons: Even more than for most declining bumble bees, the status, current trend, severity of threats, and prognosis for B. pensylvanicus are very unclear. It is not even clear that the causes of the decline are similar to those causing large-scale crashes and extirpations of subgenus Bombus species, although they probably are. While apparently widespread (reportedly from Vermont to Mexico), the decline of this species, and the closely related more western B. fervidus, is less well documented and almost certainly not as rapid compared to most species of subgenus Bombus. Still, there is no basis to suggest whether this species will be widespread but less common, stabilize (and perhaps even remain common) in a greatly reduced range, reduced to scattered refugia, or completely extinct by 2020. Put another way, within about a decade the conservation status rank could plausibly be anything from GX (extinct) to G4 (apparently secure). Decline is already underway and not speculative, although the exact causes are uncertain. Since it is declining a bit more slowly compared to species in subgenus Bombus, there may be more time for B. pensylvanicus to evolve some resistance to whatever is causing the decline--especially if the main cause of decline is exotic pathogens or parasites to which some bumblebees are relatively resistant. On the other hand, B. pensylvanicus does not penetrate widely into very cold regions, which seem to be the current refugia for two more seriously declining species, B. occidentalis and B. terricola. There is no really apparopriate rank for severely declining, but once very widespread, species, especially when extinction within a few decades is a plausible outcome but so is recovery. Information on the status of B. p. sonorus since 2000 is especially limited. The G3G4 rank produced by NatureServe's Rank Calculator is accepted for now, but at best this is a snap shot in time for a rapidly changing situation. This species should be re-evaluated after the 2015 field season. An important consideration will be whether it is still turning up relatively frequently in the central states, as in 2005-2010.

Intrinsic Vulnerability: Moderately vulnerable

Comments: Queens of this species begin activity later in the season than most others (Grixti et al., 2009), a trait that is shown by Williams et al. (2009) to predispose bumblebees to declines in various parts of the world.

Environmental Specificity: Broad. Generalist or community with all key requirements common.

Canada

Rounded National Status Rank: NU - Unrankable

United States

Rounded National Status Rank: NU - Unrankable

Global Short Term Trend: Decline of 30-70%

Comments: Dr. Sydney Cameron's website (2009) notes that this species has been widely reported as declining, including B. p. sonorus. It is suspected to be declining in Vermont (Richardson, 2008) and Minnesota (DeVore, 2009), and was not found at all by Colla and Packer (2008) in southern Ontario, which represents a statistically significant decline there (see also williams et al., 2009). Grixti et al. (2008) document a large decline in relative abundance and distribution in Illinois during 2000-2007 compared with 1950-1999. However, the species still occurs there in moderate numbers. They observed 160 in 2007. Among the other 15 species of bumblebees known to occur in Illinois, they saw none of four species, and over 1000 for two others. On the other hand, all three South Dakota specimens found in Johnson's (2009) compilation of specimen data were collected in 2008. The species was not represented in collections from the 1920s to 1970s there. Garner (2011) reported Rankin county, Mississippi in August 2008. There have been other recent records in the central portion of the US. The extent and severity of the decline is uncertain, but apparently substantial. So far the species is not known to be actually extirpated over any large area--although it might be in Ontario and perhaps parts of the Northeast and Midddle Atlantic States. It was not noted as declining in the Smokies by Super and Moyer (2003), but that now needs to be considered a historic, not current, status assessment

Global Long Term Trend: Increase of 10-25% to decline of 70%

Comments: Same as short term trend. Decline started by or soon after 1998.

Comments: The severity and exact nature of the threats are uncertain, and the selection of "moderate" for severity may soon prove too conservative. The very recent declines or suspected declines reported from Vermont to Mexico suggest that some of the same factors that are causing the much more extreme, or at least more rapid, declines of species in subgenus Bombus, such as some, but perhaps not all, of the same pathogens (see Otterstater and Thomson, 2008; Federman, 2009). Habitat changes and perhaps pesticides could also be factors in some places, but and the species is persisting as of 2007 in Illinois in close to "worst case" habitat conditions (Grixti et al., 2008), and their data indicate the species did not decline much there during the mid 20th century as would be expected if habitat loss were the main factor. Furthermore there has not been any habitat change so pervasive as to cause a sudden decline apparently from Vermont to Illinois and into Mexico since 1998. Pesticides would be expected to cause local extirpations only, and of all bumblebees in the area not just declines or extirpations of two subgenera. Unlike most declining or disappearing bumblebees in the US this one does have a late phenology (Grixti et al., 2009) which Williams et al. (2009) document as a risk factor predisposing such species to declines.

If pesticides are an important factor in bumblebee declines, systemic ones such as neonicotinoids that might reach lethal concentrations in nectar or "guttation drops" (Girolami et al., 2009) would be the most likely suspects. As those authors point out guttation drops are formed by many plants, especially grasses, are consumed by honeybees, and contain neonicotinoid concentrations well above the lethal dose for honeybees. They directly demonstrate that consumption of guttation drops from corn grown from neonicotinoid-treated seeds causes death of the bees within minutes. They also review information on concentrations in nectar and pollen which are generally below lethal levels (for honeybees at least) but are still suspected by some to be impacting bees, including contributing to "colony collapse disorder". Widespread use of these systemic toxins to control grubs, sucking insects, and other pests may explain seasonal (spring) declines of honeybees in the region of Italy where this research was conducted. Queen bumblebees consuming guttation drops in spring could be quickly killed or behaviorally impaired before they complete their nest, later in the season exposed workers would be affected. It is apparently unknown to what extent bumblebees drink guttation drops.

Global Protection: Unknown whether any occurrences are appropriately protected and managed

Comments: Many colonies and even substantial populations occurred, or recently occurred, in protected places. But given the uncertainties regarding the decline, and the strong possibility of exotic pathogens being a major factor, it cannot be concluded with any confidence that such populations really are in any meaningful way protected.

Studies have found the American bumble bee to be a significant pollinator of several plants, including the federally endangered Alabama leather flower (Clematis socialis). These bees visit the Alabama leather flower plants with great frequency resulting in a high single-visit seed set. In the Chihuahuan Desert, the American bumble bee is one of the main pollinators of lechuguilla (Agave lechuguilla) - an indicator species for the Chihuahuan Desert. American bumble bee queens and workers are important pollinators of wavyleaf or pale purple coneflower (Echinacea simulata) and males are the major pollen carriers of tall or rough blazing star (Liatris aspera). Morning glory (Ipomoea purpurea and Ipomoea hederacea) is commonly pollinated by the American bumble bee, as is the yellow fringeless orchid (Platanthera integra). The American bumble bee is also known to forage on tall ironweed ( Veronia gigantea ), red clover (Trifolium pretense), Queen Anne's lace (Daucus carota), and sunflower (Helianthus spp.)

Stewardship Overview: The following is a summary of the management and conservation needs for the genus Bombus. There is a lot of literature on the decline of bumblebees and other pollinators (e.g. Goulson et al. 2005, Brown and Paxton 2009, Evans et al. 2008, and the Committee on the Status of Pollinators in North America 2007). Byrne and Fitzpatrick (2009) review pollinator conservation programs at national, regional, and global levels. DeVore (2009) offers many practical considerations for pollinator conservation in the U.S. Noordijk et al.'s (2009) discussion of mowing in Europe should be generally applicable in North America, especially northern portions. Goulson et al. (2005), among others, make more general recommendations.

It is generally agreed that declines, and in some regions extirpations, of bumblebees and other pollinators in Europe have been due primarily to habitat loss or alteration, including changes in forage plant availability (due especially to intensification of agriculture). In turn, some plants have declined due to loss of pollinators. Brown and Paxton (2009), based in the United Kingdom, suggest that future conservation strategies need to "prioritise (i) minimising habitat loss, (ii) making agricultural habitats bee-friendly, (iii) training scientists and the public in bee taxonomy and identification, (iv) basic autecological and population genetic studies to underpin conservation strategies, (v) assessing the value of DNA barcoding for bee conservation, (vi) determining the impact of invasive plants, animals, parasites and pathogens, and (vii) integrating this information to understand the potential impact of climate change on current bee diversity." Some needs may be different in the U.S. In particular, climate change is probably less of a concern, whereas parasites and diseases are of much greater immediate concern.

Williams et al. (2009) examine various hypotheses from the literature as related to the status of bumble bees in North America, Europe and China, including competition with congeners, climatic specialization, proximity to climatic range edge, food specialization, phenology, body size, and range size. Food specialization would be in part an index of habitat specialization, but possible special needs for overwintering or nesting sites are not addressed. Results of their meta-analysis of correlations showed support for the hypotheses that decline susceptibility is generally greater for species that have greater climatic specialization, in areas where species occur closest to the edges of their climatic ranges, and for species that have queens that become active relatively late in the year. At least on a multi-continent scale the other factors apparently do not widely explain bumblebee declines. Notably most North American bumble bees range through more than ten degrees of latitude and thus have adapted to a wide array of climates at least in terms of temperature, and some range from coast to coast, which requires adaptation to a wide array of precipitation regimens and habitat types as well. While climate change could impact bumble bees positively or negatively at the edges of their ranges, this is not a plausible explanation for range-wide declines of widespread species.

Williams et al. (2009) suggest that late queen phenology may render a species at a particular disadvantage when they have long colony cycles if there are losses of food plants in mid to late colony development. Among declining species in the Grixti et al. (2009) tabulation (see also Colla and Packer, 2008) two are early, one is intermediate, and two are late; the ratio is nearly the same for non-declining species six are early, one is intermediate and three are late, and late species are not over-represented among declining species (chi2=0.6, df=2, p=0.95). In contrast B. affinis, which is undergoing extreme decline and may be on the brink of extinction, has early queen phenology, as does B. terricola which is also in severe decline. Their phenologies should make them among the least at risk. Phenology is not driving the extremely rapid declines of these species. The meta-analysis of Williams et al. (2009) also does not support any relationship between declines and tongue length as some earlier studies suggested--long tongues generally indicate more specialized foragers. The data in Grixti et al. (2009) are consistent with this finding: among declining species two have short tongues, one is intermediate and two have long tongues while among non-declining species four have short tongues, four are intermediate and two have long tongues, again nearly identical (chi2=0.9, df=2, p=0.885). Some other factor, almost certainly diseases and parasites (Colla et al., 2006, Otterstatter and Thomson, 2008; Federman, 2009), is largely overriding phenology, tongue length (foraging ecology) and other life history traits that may be important determinants of risk in other countries leading to very rapid declines. Nevertheless managers should be aware of these ecological traits that may predispose species to future declines, or may be driving slower current declines. Practical implications include a need for legumes and other flowers favored by long-tongued species and for a reliable supply of flowers late in the season.

Habitat fragmentation can also be important in bumblebee ecology (Hines and Hendrix 2005). A study by Bhattacharya et al. (2003) near Boston documented that foraging bumble bees (Bombus impatiens, B. affinis) have high site fidelity and flower constancy, and are reluctant to cross roads and railroads compared to more natural habitats. If the flower supply runs out they are more likely to locate another on the same side of a road rather than to cross it. Thus like many animals, bumblebees should benefit from reducing the number of roads, and the amount of other highly unnatural habitats, such as lawns, in and near natural areas.

Bumble bees have three critical sets of ecological needs: suitable overwintering places for the queens, suitable nesting microhabitats, and adequate flowers for foraging throughout the length of the colony cycle. This cycle is several months, typically mid spring to mid or late summer. Little information was found regarding hibernation sites, and information on nesting sites is usually rather general, except that Carvell (2002) discusses the nesting habits of the subgenus Thoracobombus. These are known in England as carder bees and they "nest on the ground surface and comb together material from around the nest as a covering" and "therefore require moss and dried grasses, often in the form of disused small mammal nests... hence the importance of undisturbed tall grassland with sufficient sunlight providing warmth to the surface nest." Most other bumblebees nest below ground in pre-existing cavities. Bombus impatiens will also use a variety of man-made situations such as under houses or old rodent nests in cardboard boxes, etc. (D. Schweitzer, pers. obs in New Jersey). Plath (1922, 1927) provides detailed observations of the nesting habits of North American bumble bees, including the now seriously imperiled B. (Bombus) affinis, the nests of which he observed to be solely subterranean. Prior to its decline, B. affinis had adapted well to urban areas and was observed nesting in the concrete rubble beside the foundation of buildings (Super and Moyer, 2003). Queen bumblebees probably usually hibernate in the leaf litter near the soil surface or perhaps underground.

Other than plowing (Hopwood, 2008, DeVore 2009), most common management activities should not directly affect underground nests. However bumblebees above ground in grasses would be vulnerable to fires, and to mowing if the blade is low enough to destroy them. Hibernating queens could be very vulnerable to prescribed burns if they are above ground in dry microhabitats. However, this might not affect the population in situations where nest sites are limiting such that many queens fail to establish colonies. Prescribed burning or any other management scheme potentially can have two sets of impacts, and the latter could be positive or negative: direct mortality to the pollinators and changes in vegetation composition and structure. Prescribed burning would likely render an area unsuitable for Bombus (Thoracobombus) for at least one season due to removal of nesting microhabitats (see Carvell, 2002). Much more information is needed regarding impacts of common management practices, perhaps especially fire, on bumblebees. In general maintaining healthy rodent populations in habitats where bumblebees nest should improve availability of nest sites. Besides providing habitat and cover for native rodents, elimination of free-roaming cats could be beneficial. In addition to a likely reduction in small rodents overall, high cat numbers may lead to an increased ratio of the non-native house mouse (Mus musculus) over native mice (Peromyscus spp.) (Hawkins, 1998, as cited by Longcore et al., 2009). It is not clear whether the species mix of small rodents has much affect on the availability of bumblebee nest sites. Besides old rodent holes and grass clumps, logs may provide useful nesting sites.

Most management activities involving bumblebees will be aimed at improving flower availability. Bumblebees depend on both nectar, mainly for carbohydrates, and pollen, for protein. A queen bumblebee needs nectar when she leaves hibernation, and for another month or more while she alone rears the first brood of workers. After that, workers need access to nectar and pollen for several months. Bumblebees will travel several kilometers. For example Schmidt and Jacobson (2005) note that B. pensylvanicus sonorus commonly flies to high elevations from desert nesting sites much lower, the vertical distance alone is often over a kilometer. Devore (2009) considers a mile (1.7 km) as about the typical distance over which bumblebees forage. Citing several studies (e.g. Dramstad, 1996), Hines and Hendrix (2005) state that bumble bees routinely forage up to 600-650 m from their nests. While some bumble bees are more generalized in their preferences than others, none are thought to be highly specialized in their foraging needs. Carvell (2002) found that the more common species in her study areas in England used between about nine and 15 plant species over the course of her study. Hines and Hendrix (2005) observed bumblebees foraging on 43 of 150 species of flowers monitored in Iowa prairie remnants. Bumblebee species with longer tongues tend to visit legumes and other plants with long corollas. Feeding is most efficient if the length of the tongue and corolla are similar. Thus habitats with a greater diversity of plants with varying corolla lengths can be expected to have a richer bumblebee fauna than less diverse communities.

Carvell (2002) in England found that "Numbers of both long- and short-tongued bumblebee species, abundance of all bumblebees and species richness per quadrat were significantly positively correlated with abundance of P[ilosella] officinarum and T[rifolium] pratense (red clover), total flower abundance, flowering plant species richness and continuity of bee-exploited species (the last excepting long-tongued bumblebee species)." Habitats most likely to have these features are generally open with simple vegetation structure and little moss or thatch cover. Gardens, even those in urban areas (Wojcik et al. 2008, Fetridge et al. 2008), can be useful foraging resources for bumblebees, as can croplands (e.g. Turnock et al. 2007) if they are not sprayed with insecticides during the flowering period. Hay fields with abundant red clover or alfalfa can be major foraging habitats. Roadsides with restored native prairie vegetation can also be very beneficial (Hopwood, 2008). Prairies, moist meadows, and restored roadsides with native flowers probably are among the most productive bumblebee foraging habitats. Tuell et al. (2008) provides many records of bees, including bumble bees, at native wild flowers in Michigan. Many other studies provide useful information about species of flowers visited by bumblebees (e.g. Hopwood, 2008, US fish and Wildlife Service, 1999, 2008, DeVore, 2009). Evans et al. (2008) provide summaries of plants known to be visited by three seriously declining or imperiled species of subgenus Bombus. Hopwood (2008) documents that in Kansas, roadsides restored to native prairie vegetation supported richer bee faunas than weedy roadsides or even local prairie remnants. Similarly Noordijk et al. (2009) discuss roadsides as important habitats for pollinators, including bumblebees, in northern Europe, and discuss the suitability of various mowing regimens. For Bombus species Hopwood had 37 observations of seven species on restored roadsides versus 10 representing two species on weedy controls. She concluded that infrequently mowed roadsides with diverse native flora actually make good native bee habitat because such places are not plowed, and thus are good nesting [and probably hibernating] habitats, and unlikely to be developed for other uses. She suggests roadsides could be important to pollinator management in much of the world.

The recommendations of DeVore (2009), which are specifically for heavily agricultural southern Minnesota and for bees in general, would apply to bumblebees almost anywhere in eastern and central North America. The following quote provides guidance for making farms and other landscape pollinator-friendly not just of bumblebees, but for bees in general: "Native wildflowers can provide excellent foraging for pollinators. So can cover crops that are allowed to flower. Reducing tillage causes less disruption of nesting habitat, because two-thirds of bees nest underground. Leaving logs, stumps, snags, and clumps of grass will provide nesting sites for the rest. Fencerows with willow, dogwood, or other flowering plants provide foraging habitat on working farmland without disrupting the agronomic productivity... Roadsides, ditches, and buffer strips can also serve as wild pollinator habitat." In some cases the pollination service will have significant economic benefits. Even narrow strips of buffer land can have important impacts on bees (Hopwood, 2008, DeVore, 2009). While suburban and urban gardens do provide nutrition (but sometimes also toxic pesticides) to wild bees (Frankie et al., 2009, McFrederick and LeBuhn, 2006), manicured lawns are among the least useful nesting and foraging habitats. DeVore also points out that protection from insecticides may be needed and that several studies find low levels of many pesticides in hives, brought in by workers on contaminated pollen. While levels are usually sublethal there may still be impacts to hive success. Recent articles (e.g. Colla and Packer, 2008) have suggested persistent neonicotinoid insecticides might be particularly hazardous to bees, but so far these have not been directly linked to major local declines.

On more natural lands, management would likely focus on maintaining diverse assemblages of primarily native flora, such that flowers would be constantly available throughout the active season, typically about April to September in many places. In some areas several different habitats would be needed to fulfill this need. To the extent practical, productive foraging sites should not be mowed during the flowering season, although in most contexts foraging workers will probably locate alternative flowers. Noordijk et al. (2009) found that while mowing virtually eliminates nectar for a period of days or longer afterward, summer mowing often stimulates re-flowering that benefits the bees later in the season. Also growing season mowing could be highly detrimental to other taxa of conservation concern, such as Lepidoptera larvae that could be killed directly--in some cases an entire population. Carvell (2002) found cattle grazing to be an effective management tool in England.

Regardless of the suitability of habitat management on a local scale, the surrounding landscape context will affect bumblebee communities. Hines and Hendrix (2005) found that variation in the availability of floral resources, especially as determined by the extent of land in grassland, in the surrounding 500-700 meter radius around prairie remnants explained most difference in the bumblebee community in prairie remnants, with the abundance of suitable flowers on site also being important. Landscape context is also likely to be important in terms of suitable nesting and hibernation sites, since these habitats may not be the same as foraging areas (e.g. Carvell, 2002). Thus small scraps of habitat may be poorly suited for bumblebee conservation even if the flora is relatively pristine. Ideally management aimed at conserving local bumblebees should be tailored to the needs of the local fauna, but in general unplowed, open, diverse, flowery habitats will be the goal. In most places such habitat will need active management--the exact nature of which may be determined by factors unrelated to bumblebees. Some degree of connectivity to other suitable habitats may be necessary, which is one reason roadside, power lines, and other long corridors may be quite suitable. See Russell et al. (2005) for a useful discussion of power line management as it relates to bees.

While habitat changes, especially a large-scale decline in foraging plants in some regions such as highly agricultural parts of the Midwest, have undoubtedly impacted North American bumblebees, these do not appear to be driving declines to anywhere near the extent they are in Great Britain. There is little that can be done to address what appears to be the greatest conservation need of the most imperiled North American bumble bees: protection from Nosema, Cirthidia, and other (mostly non-native) pathogens and parasites. For the most severely impacted species, Bombus affinis, B. franklini, and other species of subgenus Bombus, unless these can be mitigated in the near future or the species evolve some resistance, any conservation efforts are likely to be moot. Nosema could not be effectively managed in commercial hives of the closely related B. occidentalis and catastrophic outbreaks lead directly to the discontinuation of commercial use of that species. There is even less that can be done to protect wild bumble bees, and evolution of natural resistance may be needed for some species to persist in major portions, or all, of their ranges, although hypothetically the same result could be accomplished by genetic engineering. About the only suggestion now is to try to minimize contact between wild bumblebees and green house bees, especially of the same subgenus. Wild bees from near green house colonies tend to have higher infection rates than more distant ones (Colla et al., 2006). Several authors have pointed out the need for tight restrictions on the importation of bumblebees, whether of native or non-native species, that have been reared outside of North America.

Comments: Based the discussion of apparently intermediate phenotypes in populations in northern Mexico and southwest Texas (Williams 2008), and limited DNA evidence being consistent with such a designation (Cameron et al. 2007), B. sonorus is treated as conspecific with B. pensylvanicus despite minor differences in genitalia of at least some males. It could be treated as a primarily Mexican subspecies as was done by Di Trani de la Hoz (2006). The ecology and phenology of this taxon in Mexico seems similar to that of populations much farther north. However, Schmidt and Jacobson (2005) report that in the Arizona mountains this species nests lower on the slopes and in the desert, unlike any other bumblebees there. They treat it as a separate species and as a foraging visitor only to the "Sky Islands" where other bumblebees nest, these observations and more so the absence of this taxon in cooler northern Arizona tend to suggest it may be a different species. More information and probably more specimens from Texas and Mexico will be needed to resolve the taxonomy for certain and it is possible these are two species that hybridize occasionally in a small area of contact. For now it is included within B. pensylvanicus here.

Described in 1773 by De Geer, who originally placed it in genus Apis.