Conservation and Management of North American Bumble Bees - By Dale F. Schweitzer, Nicole A. Capuano, Bruce E. Young, and Sheila R. Colla
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Conservation and
Management of
North American
Bumble Bees
By
Dale F. Schweitzer, Nicole A. Capuano,
Bruce E. Young, and Sheila R. Colla
A product of the USDA Forest Service and NatureServe
with funding from the National Fish and Wildlife Foundation
Executive
Summary
This document provides a brief over- Management recommendations center on providing suitable nesting and foraging
view of the diversity, natural history, habitat in close proximity during the annual period of bumble bee activity. The major
conservation status, and manage- recommendations are:
ment of North American bumble Minimize exposure to pesticides.
bees, genus Bombus. The spring to • Avoid spraying while a crop is in bloom.
late summer period of colony found- • When spraying is necessary, do so under conditions that promote rapid breakdown
of toxins and avoid drift.
ing, build up, and production of • Provide habitat for nesting and overwintering sites.
reproductive individuals, followed • Leave unplowed, undisturbed areas with logs and clumps of grass where bumble
This version corrects an error in Figure 1 that appears in the print version. Nunavut has been distinguished from by the overwintering of new queens bees can find nesting and overwintering sites.
Northwest Territories and the geographic projection has been changed to better depict northern North America. provide the natural history basis for • When nesting sites are limited, consider providing artificial nest boxes.
• Assure continuity of nectar and pollen resources when bumble bees are active from
management considerations of the spring to late summer.
approximately 46 North American • Increase abundance and diversity of wild flowers, suitable garden flowers, crops,
species. Most bumble bee species are and even weeds to improve bee density and diversity.
• Mow when bumble bees are dormant, if possible.
currently not threatened or docu-
• When summer mowing is necessary, stagger fields to ensure that some flowers are
mented as declining except in areas always available.
of intensive agriculture. Eight spe- • Time prescribed burns as recommended for mowing.
cies from three subgenera, however, • Ensure that nesting habitat is in close proximity (500-800 m; 0.3-0.5 mi) to foraging
habitat.
have declined drastically during the
• Encourage agricultural authorities to place tight restrictions on the use of bumble
last 15-20 years. These include three bees for crop pollination to prevent the spread of diseases.
species that are obligate parasites
After reviewing the literature on bumble bee conservation and management, a number
on other declining species. The of gaps in our knowledge about bumble bee biology become apparent. These gaps, listed
Report coordination by Pollinator Partnership pathogen spillover hypothesis, which here to stimulate research in different regions of North America, include:
Designer: Marguerite Meyer • How are bumble bee populations changing over time?
proposes that diseases from infected
• How important are forested habitats for bumble bee diversity?
commercial colonies imported from • What habitats do bumble bees use for overwintering?
Europe are infecting native popula- • How do habitats, including human-altered ones, vary in quality for bumble bees?
Dale F. Schweitzer1, Nicole A. Capuano1, tions of closely related species, may • Do areas where severely declining species remain share common habitat or climatic
Bruce E. Young1, and Sheila R. Colla2 explain the sharp declines of most features?
• What are the foraging needs and diet breadth of bumble bee species?
species. Other threats to bumble
1
NatureServe, 4600 North Fiarfax Dr., Floor 7, Arlington, VA 22203 • How are bumble bees affected by fire and fire management?
bees include climate change, loss of • How do toxins affect bumble bees differently from honey bees?
2
Biology Department, York University, Toronto, ON, Canada
nesting and foraging habitats and • How broad is the threat of diseases from non-native bees spilling over to native
pesticide use. bumble bees?
Cite this document as: Schweitzer, D.F., N.A. Capuano, B.E. Young, and S.R. Colla. 2012. Conservation and management of North
American bumble bees. NatureServe, Arlington, Virginia, and USDA Forest Service, Washington, D.C.
Conser vation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 3
Executive
Summary
This document provides a brief over- Management recommendations center on providing suitable nesting and foraging
view of the diversity, natural history, habitat in close proximity during the annual period of bumble bee activity. The major
conservation status, and manage- recommendations are:
ment of North American bumble Minimize exposure to pesticides.
bees, genus Bombus. The spring to • Avoid spraying while a crop is in bloom.
late summer period of colony found- • When spraying is necessary, do so under conditions that promote rapid breakdown
of toxins and avoid drift.
ing, build up, and production of • Provide habitat for nesting and overwintering sites.
reproductive individuals, followed • Leave unplowed, undisturbed areas with logs and clumps of grass where bumble
by the overwintering of new queens bees can find nesting and overwintering sites.
provide the natural history basis for • When nesting sites are limited, consider providing artificial nest boxes.
• Assure continuity of nectar and pollen resources when bumble bees are active from
management considerations of the spring to late summer.
approximately 46 North American • Increase abundance and diversity of wild flowers, suitable garden flowers, crops,
species. Most bumble bee species are and even weeds to improve bee density and diversity.
• Mow when bumble bees are dormant, if possible.
currently not threatened or docu-
• When summer mowing is necessary, stagger fields to ensure that some flowers are
mented as declining except in areas always available.
of intensive agriculture. Eight spe- • Time prescribed burns as recommended for mowing.
cies from three subgenera, however, • Ensure that nesting habitat is in close proximity (500-800 m; 0.3-0.5 mi) to foraging
habitat.
have declined drastically during the
• Encourage agricultural authorities to place tight restrictions on the use of bumble
last 15-20 years. These include three bees for crop pollination to prevent the spread of diseases.
species that are obligate parasites
After reviewing the literature on bumble bee conservation and management, a number
on other declining species. The of gaps in our knowledge about bumble bee biology become apparent. These gaps, listed
Report coordination by Pollinator Partnership pathogen spillover hypothesis, which here to stimulate research in different regions of North America, include:
Designer: Marguerite Meyer • How are bumble bee populations changing over time?
proposes that diseases from infected
• How important are forested habitats for bumble bee diversity?
commercial colonies imported from • What habitats do bumble bees use for overwintering?
Europe are infecting native popula- • How do habitats, including human-altered ones, vary in quality for bumble bees?
Dale F. Schweitzer1, Nicole A. Capuano1, tions of closely related species, may • Do areas where severely declining species remain share common habitat or climatic
Bruce E. Young1, and Sheila R. Colla2 explain the sharp declines of most features?
• What are the foraging needs and diet breadth of bumble bee species?
species. Other threats to bumble
1
NatureServe, 4600 North Fiarfax Dr., Floor 7, Arlington, VA 22203 • How are bumble bees affected by fire and fire management?
bees include climate change, loss of • How do toxins affect bumble bees differently from honey bees?
2
Biology Department, York University, Toronto, ON, Canada
nesting and foraging habitats and • How broad is the threat of diseases from non-native bees spilling over to native
pesticide use. bumble bees?
Cite this document as: Schweitzer, D.F., N.A. Capuano, B.E. Young, and S.R. Colla. 2012. Conservation and management of North
American bumble bees. NatureServe, Arlington, Virginia, and USDA Forest Service, Washington, D.C.
Conser vation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 3
where appropriate. The biblio- and Europe. As in the rest of the world, group of North American bumble varying degrees with body heat to speed growth. This
Bombus insularis.
graphic references provide an entry bumble bee diversity in North America bees, occurring from subtropical to adaptation is probably among the reasons why
Photo James Strange
point into the growing literature on is lowest in the southern lowlands and boreal zones. bumble bees can thrive in cool conditions. As in
bumble bees. Because scientific papers on highest in cooler northern and mountain Subterraneobombus (2 species)—A all social bees, workers are females. Workers
bumble bees are being published with in- regions (Figure 1). For example, most long-tongued, underground-nesting do not mate, but can reproduce by laying
Introduction creasing frequency (Goulson et al. 2010), bumble bees in Arizona occur only in the group primarily occurring in open unfertilized eggs, producing males. At the
we recognize that this document provides mountains. This pattern is opposite of northern and montane areas, such as end of the colony cycle, queens also lay
Bumble bees are a familiar component of
a snapshot of the state of our current most plant and vertebrate groups, which meadows. unfertilized eggs that become males.
our terrestrial fauna. In the past, sight-
knowledge and that subsequent research generally decrease in diversity with Thoracobombus (2 species)—A wide-
ing a bumble bee may have elicited no If nectar and pollen resources are ad-
will fill in some of the knowledge gaps we latitude. spread group occurring throughout
more than a mental note to avoid getting equate, the colony will produce males
identify here. the Northern Hemisphere as well as
stung or at most wonderment at how they In North America, the genus Bombus and new queens from about June to
can be active on high mountains or in comprises eight subgenera. These are: New World tropical mountains. In October, depending on the species,
cold climates. Today we pay them much Diversity Alpinobombus (4 species)—Bumble North America these species have latitude and elevation. The males
more attention. Precipitous population bees of the arctic and high alpine areas. long tongues and tend to nest above and queens feed and then mate.
declines have affected several species, Of the 250 species of bumble bees recog- ground. In the fall, the new queens locate
nized by taxonomists, approximately 46 Bombias (2 species)—A small group
creating cause for conservation concern. of bumble bees that occur primarily in a suitable site to overwinter (for
In addition, the loss of introduced honey occur in the U.S. and Canada (See Ap- example, mulch, rotting logs, or
bees (Apis mellifera) in both managed and pendix for notes on species classification open grasslands. Natural History loose soil). The males, workers,
used here). All North American species Bombus (5 species)—“Typical”
feral colonies has increased the need for Annual Cycle.— North American and old queen all die by the
are native to the continent. Most species bumble bees that occur in a variety of
native pollinator species. Bumble bees are bumble bee species vary somewhat in onset of winter.
have fairly broad ranges either east or temperate and boreal habitats.
generalist pollinators, performing a key their natural history. Bumble bees gener-
west of the Rockies or across northern Cullumanobombus (5 species)—Most- Foraging and nutrition.—
function in their ecosystems. They also ally produce one generation per year. In
Canada, although a few such as Bom- ly bumble bees of high alpine grass- The workers gather nectar and
form a significant portion of the native the spring, queens emerge from hiberna-
bus franklini in northern California and lands and semi-desert. pollen to satisfy both their own
insect community that pollinates crops tion to feed on flower nectar and search
southern Oregon have restricted ranges. Psithyrus (6 species)—“Cuckoo” bees nutritional needs and those
worth $3 billion each year in the United for nest sites, which may be above or
Six species, including three of the four that parasitize nests of other bumble of the nest. Adults depend
States (Losey and Vaughan 2006). For below ground, or either, depending on
North American species in the subgenus bees. on nectar for carbohydrates
both of these reasons, land managers are the species (Thorp et al. 1983, Kearns
Alpinobombus extend their ranges to Asia and gather pollen as a protein
increasingly interested in bumble bee Pyrobombus (20 species) —The largest and Thomson 2001, McFrederick and
source for larvae. A queen
conservation and management (Goulson LeBuhn 2006). Bumble bees frequently
bumble bee forages for nectar
et al. 2010). inhabit abandoned rodent nests, probably
when she emerges in the spring,
because these structures insulate the bees
This document summarizes recent and for another month or more
from cold temperatures. Nests also tend to
information about bumble bee declines while she alone rears the first
be constructed in areas with south facing
and their management in North America. brood of workers, during which
exposures. Species nesting above ground
By “bumble bee”, we refer to species of time she must also collect pollen to
may use long grass or hay stacks. A few
the genus Bombus (Hymenoptera, Api- feed her young.
species will use tree cavities or bird boxes
dae), including the cuckoo bumble bees
as nest sites. In urban areas, bumble bees Although some bumble bees can
in the subgenus Psithyrus. We start with
use spaces between cinder blocks, house forage up to several kilometers from
a brief overview of bumble bee diversity
foundations, abandoned furniture and their colonies in search of nectar and
and natural history to provide context
decks as protection for their growing pollen, most species probably travel
for the subsequent discussions. We then
colonies. no more than 600-1,700 m (1/3 – 1 mi)
review the conservation status of bumble
to forage (Dramstad 1996, Hines and
bees and the potential causes for their Once they locate a suitable nesting site, a
Hendrix 2005, Droege 2008, DeVore
decline. Finally, we discuss considerations queen will modify it slightly and rear a
2009). Presumably shorter foraging trips
for managing for bumble bee diversity brood (Kearns and Thomson 2001). A
are both safer and more energy-efficient. The
and abundance. Many of the resulting few weeks later, the first workers emerge.
desert subspecies B. pensylvanicus sonorus can
recommendations apply to other native These workers tend the young, maintain
ascend as much as 1,000 vertical meters (0.6 mi)
pollinators besides bumble bees, especially the nest, and assume the food provision
on a daily basis in search of food (Schmidt and
ground-nesting bees. Much research duties. The queen rarely, or never, leaves
Figure 1. Documented bumble bee diversity in states or provinces for which Jacobson 2005).
on bumble bee conservation occurs in the nest again. Like most birds, bumble
adequate data are available. Figures for some states may still represent
Europe, so we draw on this information underestimates. bees incubate their eggs and larvae to North American bumble bees have been documented
4 Conservation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 5
where appropriate. The biblio- and Europe. As in the rest of the world, group of North American bumble varying degrees with body heat to speed growth. This
Bombus insularis.
graphic references provide an entry bumble bee diversity in North America bees, occurring from subtropical to adaptation is probably among the reasons why
Photo James Strange
point into the growing literature on is lowest in the southern lowlands and boreal zones. bumble bees can thrive in cool conditions. As in
bumble bees. Because scientific papers on highest in cooler northern and mountain Subterraneobombus (2 species)—A all social bees, workers are females. Workers
bumble bees are being published with in- regions (Figure 1). For example, most long-tongued, underground-nesting do not mate, but can reproduce by laying
Introduction creasing frequency (Goulson et al. 2010), bumble bees in Arizona occur only in the group primarily occurring in open unfertilized eggs, producing males. At the
we recognize that this document provides mountains. This pattern is opposite of northern and montane areas, such as end of the colony cycle, queens also lay
Bumble bees are a familiar component of
a snapshot of the state of our current most plant and vertebrate groups, which meadows. unfertilized eggs that become males.
our terrestrial fauna. In the past, sight-
knowledge and that subsequent research generally decrease in diversity with Thoracobombus (2 species)—A wide-
ing a bumble bee may have elicited no If nectar and pollen resources are ad-
will fill in some of the knowledge gaps we latitude. spread group occurring throughout
more than a mental note to avoid getting equate, the colony will produce males
identify here. the Northern Hemisphere as well as
stung or at most wonderment at how they In North America, the genus Bombus and new queens from about June to
can be active on high mountains or in comprises eight subgenera. These are: New World tropical mountains. In October, depending on the species,
cold climates. Today we pay them much Diversity Alpinobombus (4 species)—Bumble North America these species have latitude and elevation. The males
more attention. Precipitous population bees of the arctic and high alpine areas. long tongues and tend to nest above and queens feed and then mate.
declines have affected several species, Of the 250 species of bumble bees recog- ground. In the fall, the new queens locate
nized by taxonomists, approximately 46 Bombias (2 species)—A small group
creating cause for conservation concern. of bumble bees that occur primarily in a suitable site to overwinter (for
In addition, the loss of introduced honey occur in the U.S. and Canada (See Ap- example, mulch, rotting logs, or
bees (Apis mellifera) in both managed and pendix for notes on species classification open grasslands. Natural History loose soil). The males, workers,
used here). All North American species Bombus (5 species)—“Typical”
feral colonies has increased the need for Annual Cycle.— North American and old queen all die by the
are native to the continent. Most species bumble bees that occur in a variety of
native pollinator species. Bumble bees are bumble bee species vary somewhat in onset of winter.
have fairly broad ranges either east or temperate and boreal habitats.
generalist pollinators, performing a key their natural history. Bumble bees gener-
west of the Rockies or across northern Cullumanobombus (5 species)—Most- Foraging and nutrition.—
function in their ecosystems. They also ally produce one generation per year. In
Canada, although a few such as Bom- ly bumble bees of high alpine grass- The workers gather nectar and
form a significant portion of the native the spring, queens emerge from hiberna-
bus franklini in northern California and lands and semi-desert. pollen to satisfy both their own
insect community that pollinates crops tion to feed on flower nectar and search
southern Oregon have restricted ranges. Psithyrus (6 species)—“Cuckoo” bees nutritional needs and those
worth $3 billion each year in the United for nest sites, which may be above or
Six species, including three of the four that parasitize nests of other bumble of the nest. Adults depend
States (Losey and Vaughan 2006). For below ground, or either, depending on
North American species in the subgenus bees. on nectar for carbohydrates
both of these reasons, land managers are the species (Thorp et al. 1983, Kearns
Alpinobombus extend their ranges to Asia and gather pollen as a protein
increasingly interested in bumble bee Pyrobombus (20 species) —The largest and Thomson 2001, McFrederick and
source for larvae. A queen
conservation and management (Goulson LeBuhn 2006). Bumble bees frequently
bumble bee forages for nectar
et al. 2010). inhabit abandoned rodent nests, probably
when she emerges in the spring,
because these structures insulate the bees
This document summarizes recent and for another month or more
from cold temperatures. Nests also tend to
information about bumble bee declines while she alone rears the first
be constructed in areas with south facing
and their management in North America. brood of workers, during which
exposures. Species nesting above ground
By “bumble bee”, we refer to species of time she must also collect pollen to
may use long grass or hay stacks. A few
the genus Bombus (Hymenoptera, Api- feed her young.
species will use tree cavities or bird boxes
dae), including the cuckoo bumble bees
as nest sites. In urban areas, bumble bees Although some bumble bees can
in the subgenus Psithyrus. We start with
use spaces between cinder blocks, house forage up to several kilometers from
a brief overview of bumble bee diversity
foundations, abandoned furniture and their colonies in search of nectar and
and natural history to provide context
decks as protection for their growing pollen, most species probably travel
for the subsequent discussions. We then
colonies. no more than 600-1,700 m (1/3 – 1 mi)
review the conservation status of bumble
to forage (Dramstad 1996, Hines and
bees and the potential causes for their Once they locate a suitable nesting site, a
Hendrix 2005, Droege 2008, DeVore
decline. Finally, we discuss considerations queen will modify it slightly and rear a
2009). Presumably shorter foraging trips
for managing for bumble bee diversity brood (Kearns and Thomson 2001). A
are both safer and more energy-efficient. The
and abundance. Many of the resulting few weeks later, the first workers emerge.
desert subspecies B. pensylvanicus sonorus can
recommendations apply to other native These workers tend the young, maintain
ascend as much as 1,000 vertical meters (0.6 mi)
pollinators besides bumble bees, especially the nest, and assume the food provision
on a daily basis in search of food (Schmidt and
ground-nesting bees. Much research duties. The queen rarely, or never, leaves
Figure 1. Documented bumble bee diversity in states or provinces for which Jacobson 2005).
on bumble bee conservation occurs in the nest again. Like most birds, bumble
adequate data are available. Figures for some states may still represent
Europe, so we draw on this information underestimates. bees incubate their eggs and larvae to North American bumble bees have been documented
4 Conservation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 5
visiting hundreds of native and intro- ated with more tended consequence of causing the demise ing rarity, threats, and population trends range (Colla and Packer 2008, Grixti et al.
duced plant genera (Robertson 1929, open habitat (Colla of several native bumble bees (see Causes (Master et al. 2009). Of the North Ameri- 2008), but not as sharply as other declin-
Mitchell 1962, Colla and Dumesh 2010). and Dumesh 2010). The of Declines). can bumble bee species, nearly four-fifths ing species. This species, B. vagans, is still
Some species are more generalized in disappearance of bumble are globally secure (Figure 2, Appendix). regularly found across its range. Several
their foraging preferences than others, bees in the fall appears to Severe declines in North America are other Pyrobombus have been documented
but none appear to be highly specialized. be timed with the passing Conservation Status so far limited to eight species in three as increasing. The North American spe-
In one study in Iowa prairie remnants, of native fall flowers and Declines in bumble bees and other pol- subgenera, including all four North cies in subgenera Alpinobombus, Cullo-
bumble bees foraged at 43 of 150 species often precedes the first frost linators worldwide are documented in American endemic species of subgenus manbombus, and Subterraneobombus
of flowers available (Hines and Hendrix and leaf fall (D. Schweitzer, numerous studies (Goulson et al. 2005, Bombus (the species B. moderatus is appar- all appear to have stable populations
2005). However, the extent of specialism pers. obs.). Kluser and Peduzzi 2007, Colla and ently not declining, but its status is poorly although rigorous range-wide monitoring
at the colony or individual level is largely Packer 2008, Brown and Paxton 2009, documented), B. pensylvanicus, and three data are mostly lacking.
Nest usurpation.— Spe-
unknown. Evans et al. 2008, Williams et al. 2009, species of subgenus Psithyrus. In subge-
cies of subgenus Psithyrus
Winfree 2010, Committee on the Status nus Bombus, B. franklini may already be
Activity and cold tolerance.—Bumble have no worker caste of their own.
Figure 2. Proportion of North American of Pollinators in North America 2007, extinct and B. affinis, a common species Causes of Declines
bees are well known to fly when condi- Females can reproduce only by taking bumble bee species at risk. Cameron et al. 2011a). Regional studies in the early 1990s, may be extirpated in Hypotheses about bumble bee declines in
tions are too cold for most other insects over a nest of another species. Workers
with adequate baseline data invariably 90% of its range (Williams and Osborne North American can be divided into two
(e.g. cloudy or cool days, or early in the in usurped nests tend the offspring of the
Workers of other species, such as B. show that some bumble bees are in recent 2009; Figure 3). The latter species is now classes. The first class, relating to the di-
morning before other diurnal insects are replacement queen. Entomologists have
pensylvanicus, and B. fervidus can be very decline (Giles and Ascher 2006, Colla and listed as Endangered by the Committee rect and indirect effects of climate change
active). They have a low surface area to not fully documented the host breadth of
aggressive around their nests (Thorp et al. Packer 2008, Grixti et al. 2009, Cameron on the Status of Endangered Wildlife in and habitat loss and degradation due to
volume ratio compared to other insects, North American Psithyrus. Bombus insu-
1983, Kearns and Thomson 2001), likely et al. 2011b). However, the status of Canada (COSEWIC). The status of the agricultural intensification, can explain
are well insulated, and can generate body laris preys on several subgenera, whereas
a behavioral adaptation to their above- many species throughout their ranges is cuckoo bees, subgenus Psithyrus, is similar gradual population declines and range
heat using their thoracic muscles. Bumble B. citrinus is apparently a specialist on
ground nesting habits. poorly known. Habitat loss in areas with to their hosts. Two species that commonly restrictions in bumble bees worldwide. A
bees have been reported flying at slightly subgenus Pyrobombus. Bombus ashtoni
intensive agriculture can cause regional parasitize species in Pyrobombus appear to second class of hypotheses addresses the
sub-freezing temperatures (Heinrich and B. suckleyi seem to be specialists on Pollination.—Bumble bees are impor-
extirpations of formerly common species be doing well, while three that parasitize swift and widespread declines restricted
1979). This ability to fly in cold weather the subgenus Bombus (Williams 2008b, tant generalist pollinators of native plants
(Grixti et al. 2009, Williams et al. 2009, species of subgenera Bombus and Thora- to endemic North American species.
is undoubtedly a factor in the success Laverty and Harder 1988), and B. variabi- and agricultural crops. The list of flowers
Winfree 2010). cobombus are in serious declines and may These hypotheses center on the “spillover”
of bumble bees in cool to frigid climates lis appears to be a specialist on B. pensyl- visited by bumble bees is vast (Goulson have disappeared from most if not all of of pathogens from bumble bees imported
throughout much of the world. vanicus. Queens of subgenera Alpinobom- 2010, Kearns and Thomson 2001, Thorp To determine the conservation status of their ranges. from overseas.
bus and Bombus sometimes usurp nests et al. 1983). Theoretical studies have un- North American bumble bees, Nature-
Bumble bees’ seasonal activity differs
of their own or closely related species derscored the importance of generalists in Serve assessed all species according to One species in the subgenus Pyrobombus A recent meta-analysis of bumble bees in
among species. In the Mid-Atlantic states,
(Richards 1973, Goulson 2010). maintaining pollinator networks and com- their standard assessment factors, includ- appears to be declining in some parts of its North America, Europe and China has
activity starts about the end of March for
munities of flowering plants (Memmott et suggested that species which emerge later
the earliest species and becomes minimal Aggression.—Bumble bees occasion-
al. 2004). One empirical study in Europe in the year or have narrow climatic niches
in October (Droege 2008). Some early ally sting when their nest is disturbed,
confirmed this prediction, demonstrating are likely more vulnerable to these above
species such as B. impatiens are active but rarely do so otherwise. Queens and
that the abundance of insect-pollinated threats (Williams et al. 2009). Hypoth-
into the fall, while others end their cycles workers can sting, but, as in all bees and
plants declined in areas where bumble eses that failed to explain vulnerability
in June or July (e.g., B. bimaculatus). wasps, males cannot. To humans, the
bees and other native bees had become include competition with congeners, food
Others, including B. pensylvanicus, emerge stings are briefly painful but not danger-
extirpated (Biesmeijer et al. 2006). specialization, phenology, body size, and
from their overwintering sites later in ous, except to a few people who develop
spring. The parasitic cuckoo species also serious allergic reactions. Bumble bee range extent. However, some of these
Bumble bees exhibit a behavior known
tend to have shorter cycles. In northern hives contain far fewer individuals than factors may be more important regionally
as “buzz pollination,” in which the bee
New England, activity begins a month or those of honey bees, and workers of most than in global analyses. For example, one
vibrates her wing muscles while holding
more later and ends a few weeks earlier. A species are far less aggressive than wasps European study showed that species uti-
the flower with her jaws, causing the re-
good rule of thumb in much of the eastern and hornets. Bumble bee stingers are not lizing smaller numbers of pollen sources
lease of large amounts of pollen. Growers
U.S. is that queens of the early-emerging barbed as in honey bees and therefore do have become rarer since the middle of the
of crops such as tomatoes, peppers, and
species become numerous soon after red not remain in the victim. However, this twentieth century (Kleijn and Raemak-
cranberries prize this behavior because
maple (Acer rubrum) blossoms drop and also means a bumble bee can sting more ers 2008). A brief summary of the major
it leads to better fruit set than pollination
just before blueberry (Vaccinium spp.) than once when provoked. Some species, hypotheses follows.
by honey bees. A commercial bumble
and other early Ericaceae flower. Early such as B. impatiens, are remarkably non- bee industry has emerged to capitalize on Habitat loss.—Because bumble bees
emerging species also tend to be associ- aggressive when nesting around buildings. buzz pollination for greenhouse tomato often forage in open, disturbed habitats,
ated with woodland habitats, whereas the This species is also safely managed for farmers (Velthius and van Doorn 2006), a the effects of habitat loss are harder to
Figure 3. Distribution of the Rusty-patched Bumble Bee, Bombus affinis.
later emerging species tend to be associ- crop pollination, including in greenhouses. development that may have had the unin- measure than for animals that depend
Source: NatureServe 2009.
6 Conservation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 7visiting hundreds of native and intro- ated with more tended consequence of causing the demise ing rarity, threats, and population trends range (Colla and Packer 2008, Grixti et al.
duced plant genera (Robertson 1929, open habitat (Colla of several native bumble bees (see Causes (Master et al. 2009). Of the North Ameri- 2008), but not as sharply as other declin-
Mitchell 1962, Colla and Dumesh 2010). and Dumesh 2010). The of Declines). can bumble bee species, nearly four-fifths ing species. This species, B. vagans, is still
Some species are more generalized in disappearance of bumble are globally secure (Figure 2, Appendix). regularly found across its range. Several
their foraging preferences than others, bees in the fall appears to Severe declines in North America are other Pyrobombus have been documented
but none appear to be highly specialized. be timed with the passing Conservation Status so far limited to eight species in three as increasing. The North American spe-
In one study in Iowa prairie remnants, of native fall flowers and Declines in bumble bees and other pol- subgenera, including all four North cies in subgenera Alpinobombus, Cullo-
bumble bees foraged at 43 of 150 species often precedes the first frost linators worldwide are documented in American endemic species of subgenus manbombus, and Subterraneobombus
of flowers available (Hines and Hendrix and leaf fall (D. Schweitzer, numerous studies (Goulson et al. 2005, Bombus (the species B. moderatus is appar- all appear to have stable populations
2005). However, the extent of specialism pers. obs.). Kluser and Peduzzi 2007, Colla and ently not declining, but its status is poorly although rigorous range-wide monitoring
at the colony or individual level is largely Packer 2008, Brown and Paxton 2009, documented), B. pensylvanicus, and three data are mostly lacking.
Nest usurpation.— Spe-
unknown. Evans et al. 2008, Williams et al. 2009, species of subgenus Psithyrus. In subge-
cies of subgenus Psithyrus
Winfree 2010, Committee on the Status nus Bombus, B. franklini may already be
Activity and cold tolerance.—Bumble have no worker caste of their own.
Figure 2. Proportion of North American of Pollinators in North America 2007, extinct and B. affinis, a common species Causes of Declines
bees are well known to fly when condi- Females can reproduce only by taking bumble bee species at risk. Cameron et al. 2011a). Regional studies in the early 1990s, may be extirpated in Hypotheses about bumble bee declines in
tions are too cold for most other insects over a nest of another species. Workers
with adequate baseline data invariably 90% of its range (Williams and Osborne North American can be divided into two
(e.g. cloudy or cool days, or early in the in usurped nests tend the offspring of the
Workers of other species, such as B. show that some bumble bees are in recent 2009; Figure 3). The latter species is now classes. The first class, relating to the di-
morning before other diurnal insects are replacement queen. Entomologists have
pensylvanicus, and B. fervidus can be very decline (Giles and Ascher 2006, Colla and listed as Endangered by the Committee rect and indirect effects of climate change
active). They have a low surface area to not fully documented the host breadth of
aggressive around their nests (Thorp et al. Packer 2008, Grixti et al. 2009, Cameron on the Status of Endangered Wildlife in and habitat loss and degradation due to
volume ratio compared to other insects, North American Psithyrus. Bombus insu-
1983, Kearns and Thomson 2001), likely et al. 2011b). However, the status of Canada (COSEWIC). The status of the agricultural intensification, can explain
are well insulated, and can generate body laris preys on several subgenera, whereas
a behavioral adaptation to their above- many species throughout their ranges is cuckoo bees, subgenus Psithyrus, is similar gradual population declines and range
heat using their thoracic muscles. Bumble B. citrinus is apparently a specialist on
ground nesting habits. poorly known. Habitat loss in areas with to their hosts. Two species that commonly restrictions in bumble bees worldwide. A
bees have been reported flying at slightly subgenus Pyrobombus. Bombus ashtoni
intensive agriculture can cause regional parasitize species in Pyrobombus appear to second class of hypotheses addresses the
sub-freezing temperatures (Heinrich and B. suckleyi seem to be specialists on Pollination.—Bumble bees are impor-
extirpations of formerly common species be doing well, while three that parasitize swift and widespread declines restricted
1979). This ability to fly in cold weather the subgenus Bombus (Williams 2008b, tant generalist pollinators of native plants
(Grixti et al. 2009, Williams et al. 2009, species of subgenera Bombus and Thora- to endemic North American species.
is undoubtedly a factor in the success Laverty and Harder 1988), and B. variabi- and agricultural crops. The list of flowers
Winfree 2010). cobombus are in serious declines and may These hypotheses center on the “spillover”
of bumble bees in cool to frigid climates lis appears to be a specialist on B. pensyl- visited by bumble bees is vast (Goulson have disappeared from most if not all of of pathogens from bumble bees imported
throughout much of the world. vanicus. Queens of subgenera Alpinobom- 2010, Kearns and Thomson 2001, Thorp To determine the conservation status of their ranges. from overseas.
bus and Bombus sometimes usurp nests et al. 1983). Theoretical studies have un- North American bumble bees, Nature-
Bumble bees’ seasonal activity differs
of their own or closely related species derscored the importance of generalists in Serve assessed all species according to One species in the subgenus Pyrobombus A recent meta-analysis of bumble bees in
among species. In the Mid-Atlantic states,
(Richards 1973, Goulson 2010). maintaining pollinator networks and com- their standard assessment factors, includ- appears to be declining in some parts of its North America, Europe and China has
activity starts about the end of March for
munities of flowering plants (Memmott et suggested that species which emerge later
the earliest species and becomes minimal Aggression.—Bumble bees occasion-
al. 2004). One empirical study in Europe in the year or have narrow climatic niches
in October (Droege 2008). Some early ally sting when their nest is disturbed,
confirmed this prediction, demonstrating are likely more vulnerable to these above
species such as B. impatiens are active but rarely do so otherwise. Queens and
that the abundance of insect-pollinated threats (Williams et al. 2009). Hypoth-
into the fall, while others end their cycles workers can sting, but, as in all bees and
plants declined in areas where bumble eses that failed to explain vulnerability
in June or July (e.g., B. bimaculatus). wasps, males cannot. To humans, the
bees and other native bees had become include competition with congeners, food
Others, including B. pensylvanicus, emerge stings are briefly painful but not danger-
extirpated (Biesmeijer et al. 2006). specialization, phenology, body size, and
from their overwintering sites later in ous, except to a few people who develop
spring. The parasitic cuckoo species also serious allergic reactions. Bumble bee range extent. However, some of these
Bumble bees exhibit a behavior known
tend to have shorter cycles. In northern hives contain far fewer individuals than factors may be more important regionally
as “buzz pollination,” in which the bee
New England, activity begins a month or those of honey bees, and workers of most than in global analyses. For example, one
vibrates her wing muscles while holding
more later and ends a few weeks earlier. A species are far less aggressive than wasps European study showed that species uti-
the flower with her jaws, causing the re-
good rule of thumb in much of the eastern and hornets. Bumble bee stingers are not lizing smaller numbers of pollen sources
lease of large amounts of pollen. Growers
U.S. is that queens of the early-emerging barbed as in honey bees and therefore do have become rarer since the middle of the
of crops such as tomatoes, peppers, and
species become numerous soon after red not remain in the victim. However, this twentieth century (Kleijn and Raemak-
cranberries prize this behavior because
maple (Acer rubrum) blossoms drop and also means a bumble bee can sting more ers 2008). A brief summary of the major
it leads to better fruit set than pollination
just before blueberry (Vaccinium spp.) than once when provoked. Some species, hypotheses follows.
by honey bees. A commercial bumble
and other early Ericaceae flower. Early such as B. impatiens, are remarkably non- bee industry has emerged to capitalize on Habitat loss.—Because bumble bees
emerging species also tend to be associ- aggressive when nesting around buildings. buzz pollination for greenhouse tomato often forage in open, disturbed habitats,
ated with woodland habitats, whereas the This species is also safely managed for farmers (Velthius and van Doorn 2006), a the effects of habitat loss are harder to
Figure 3. Distribution of the Rusty-patched Bumble Bee, Bombus affinis.
later emerging species tend to be associ- crop pollination, including in greenhouses. development that may have had the unin- measure than for animals that depend
Source: NatureServe 2009.
6 Conservation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 7on more natural habitats. Some agricul- that feed on pesticide-contaminated food. native bumble bees corresponds with the Several studies have found bumble bee management to be com-
tural habitats, such as hay meadows and to climate change are those that Some pesticides, such as spinosad, cause accelerated transportation of bumble bee patible with agricultural practices. Moderate grazing can be
pastures, are suitable to bumble bees occupy narrow ranges near the Pacific no direct mortality but instead reduce colonies in the mid and late 1990s after beneficial to bees in the western U.S. (DeBano 2006, Black
Providing
(Carvell 2002, Goulson 2010, McFreder- coast, such as B. crotchii in oak woodland, foraging efficiency (Goulson 2010). The the development of techniques for domes- et al. 2007). In the northwestern U.S., agricultural areas Artificial
ick and LeBuhn 2006, Rao and Stephen chaparral, and deserts and B. sitkensis and toxicity of specific pesticides is better tication. The actual pathogens implicated with blueberry (Vaccinium spp.) and red clover (Trifo- Nests for
2010). Some species can even prosper in B. caliginosus in cooler coastal climates. known for honey bees than bumble bees, are the protozoans Crithidia bombi and lium pratense) can support abundant populations of Bumble Bees
urban gardens and parks (McFrederick Elsewhere, isolated high alpine popula- but the available data suggest that toxicity Nosema bombi, although other pathogens several species of bumble bees (Rao and Stephen
and LeBuhn 2006, Matteson et al. 2008, tions of several species may disappear due to bumble bees is generally similar to that may also play important roles (Meeus et 2010). In any region, the keys are maintaining a Where nesting sites are
Matteson and Langellotto 2009). The to climate change. of honey bees (Alston and Tepedino 2000). al. 2011). Unfortunately, due to the lack reliable supply of nectar throughout the breeding limited, artificial nests
spread of Eurasian clovers (Trifolium) Phenology of queen emergence.— An application of pesticides to control of both stable populations of declining season, providing unplowed nesting habitats,
are an option to increase
and vetches (Vicia, Coronilla) has ben- Some authors suggest that species in spruce budworm in New Brunswick il- species in affected regions and informa- and limiting exposure to insecticides. Organic
efited some butterflies (Schweitzer 2006) lustrates the potential effects of pesticides tion about native pathogens, researchers farming practices may help promote bumble bumble bee populations
which queens become active later in
and presumably bumble bees as well. the season are at a disadvantage due to on bumble bees and other pollinators. In cannot directly test the effects of these bee populations, although other factors can (MacCulloch 2007, Kearns
Nevertheless, intensive agriculture has competition for nest sites and vulnerability this case, the pesticide application caused pathogens relative to other threats. confound research results (Winfree 2010). and Thomson 2001). The basic
caused local and regional declines in the to losses of food plants that are impor- blueberry crop losses due to reduced avail- Some bumble bee species can benefit from
Midwest as well as Europe (Grixti et al. ability of pollinators. In addition, reduced foraging in suburban and urban gardens, artificial nest is a box fitted with
tant in mid to late colony development
2009, Williams et al. 2009). The mismatch (Williams et al. 2009). In North America, pollination of nearby native species caused Conservation and (Frankie et al. 2009, McFrederick and a plastic pipe as an entrance
between the time scale of habitat loss nest competition is documented in urban a local wild berry shortage and conse- Management LeBuhn 2006). Manicured lawns and golf tunnel. The box can be made out
(before the mid 20th century) and rapidly areas of San Francisco where the early quently increased the number of birds courses with heavy pesticide use and de-
To complete their annual cycle, all bumble of wood (such as exterior grade
declining North American species (since B. vosnenskii apparently excludes the foraging on cultivated blueberries (Kevan void of flowers are among the least useful
bees need nesting habitat, flowers for nu-
the mid 1990s) suggests that habitat loss is later B. caliginosus and B. sitkensis from 1974). Bumble bee colonies can absorb the nesting and foraging habitats. plywood) or Styrofoam (such as
trition, and a place for queens to overwin-
unlikely to explain these declines (Grixti the limited supply of subterranean nest loss of a few workers to pesticides in sum- an old cooler). Dimensions vary
ter. They must also avoid lethal and sub- On more natural lands, management
et al. 2009). sites (McFrederick and LeBuhn 2006). mer, but worker loss can more seriously
lethal chemicals and pathogens. We know should focus on maintaining diverse as- but 8 x 8 x 6 inches (20 x 20 x 15
However, none of these species appear to impact colony survival in spring before
Climate change.—Although climate very little about overwintering needs, so semblages of primarily native flora, such
be declining globally, and there is no evi- colonies have built up significant numbers cm) is standard. The entrance
change has been suggested as a cause of the following summary of the growing that flowers would be constantly available
dence that phenology is linked to declines of workers (Goulson 2010). Additionally, hole should be ¼ inch (0.65 cm) in
declines and may be affecting bumble literature on bumble bee conservation and throughout the nesting season. In prairie
of bumble bees in North America where sub-lethal compounds may accumulate in
bees in some places, there is as of yet little management will focus on nesting and regions, restoration of native prairie diameter. The box can be placed
both early- and late-emerging species are the colony and affect the overall reproduc-
direct evidence that climate change is foraging needs. species and elimination of plowing, for ex- on the ground or 6-12 inches
among the five non-parasitic species that tive fitness of the colony. Species which
responsible for global declines of wide- ample along roadsides, can result in richer
are in severe decline. may be more vulnerable to pesticide use General habitat needs.—Bumble bees (15-30 cm) underground with the
spread species. In North America, most bumble bee faunas (Hopwood 2008).
include the above ground nesting spe- can be atypical targets for conservation
species occur (at least formerly) in a wide Tongue length and foraging ecol- entrance tube connecting the box
cies (e.g., subgenus Thoracobombus) and efforts. In contrast to many other rare The extent to which bumble bees use for-
array of climates, ranging through more ogy.—Bumble bees with long tongues are to the surface. Southern expo-
species with long colony cycles that can or endangered species, bumble bees may ests is a major knowledge gap for eastern
than ten degrees of latitude and some generally more specialized foragers. Al- accumulate toxins over the spring, sum- not require forest cover or even natural North American bumble bees, although sures, especially on a slight em-
from coast to coast. Moreover, most of though some authors have suggested that mer and fall. Pesticides likely contribute to habitats to maintain large and species-rich some species such as B. vagans seem to bankment, are best. Whatever
the North American species that have specialists (and therefore longer-tongued bumble bee declines in areas of intensive populations. Especially in eastern North be associated with wooded habitats (Colla
declined precipitously had large ranges. species) should be more likely to decline, agriculture, but are unlikely to be respon- America, a hayfield or powerline cut with the design or placement, the
and Dumesh 2010). Similarly, the effects of
Even B. affinis ranged from Maine to no such pattern has emerged in North box should contain insulation
sible for rapid, widespread declines (Colla plentiful wildflowers may be all that is standard forest management practices, such
Georgia and the Dakotas (Figure 3). America (Grixti et al. 2009, Williams et al. and Packer 2008, DeVore 2009). necessary for populations of a number of as thinning or controlled burning, on bumble in the form of upholsterer’s
Despite this large range, members of the 2009, Winfree 2010). One complication species (Russell et al. 2005). In fact, the bees are mostly undocumented. Opening forest
subgenus Bombus do seem to be some- with relating tongue length with forag- Pathogen spillover.—Currently, the cotton or polyester fiberfill.
endangered species Bombus affinis was canopies often allows more flowering of under-
what climatically restricted as they occur ing is that tongue length is individually most compelling hypothesis to explain Reported reasons for fail-
quite common in urban areas before its story plants, which should favor bumble bees (but
mostly at high elevations in southern parts variable with body size, whereas foraging rapid declines is the spillover of pathogens
collapse (Colla and Dumesh 2010). Re- see Nesting Habitat for the danger posed by fires). ure include ants, excess
of their ranges. Range breadth, combined preferences are largely learned (Kearns from managed to wild bumble bees (Colla
gardless of the region, management activi-
with high mobility and dispersal ability, and Thomson 2001). Direct measures of et al. 2006, Otterstatter and Thomson Food supply.—Observations of nest failure due to moisture, or mam-
ties should be aimed at improving flower
and the observed rapidity of declines seem foraging specialization, however, indicate 2008, Williams et al. 2009, Goulson 2010, food limitation highlight the need for a reliable nectar malian predators, so
availability and providing potential nest-
to argue against climate change as being a weak relationship with declines in Eu- Meeus et al. 2011). Field documenta- and pollen supply when bumble bees are active from
ing habitat (Blake et al. 2011). Specific managers should be
a major factor in recent dramatic declines. rope (Kleijn and Raemakers 2008). tion of pathogen spillover and related spring to late summer (Goulson 2010). In both natural
actions taken to achieve this objective will on the lookout for
However, more research is needed to modeling show waves of parasites and and anthropogenic habitats, multiple nectar plants with
Pesticides.—Direct exposure to pesticides vary depending upon whether manage-
further investigate this. pathogens spreading out from infested a succession of overlapping bloom periods are usually these problems.
can kill queen or worker bumble bees, ment is directed at agricultural, urban, or
commercial hives at multiple locations. required to satisfy this requirement. In some cases forag-
Species that may prove to be vulnerable and cause minor to lethal effects to larvae more natural lands.
Moreover, the timing of decline onset in ing habitats as well as plant species will vary seasonally. In
8 Conservation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 9on more natural habitats. Some agricul- that feed on pesticide-contaminated food. native bumble bees corresponds with the Several studies have found bumble bee management to be com-
tural habitats, such as hay meadows and to climate change are those that Some pesticides, such as spinosad, cause accelerated transportation of bumble bee patible with agricultural practices. Moderate grazing can be
pastures, are suitable to bumble bees occupy narrow ranges near the Pacific no direct mortality but instead reduce colonies in the mid and late 1990s after beneficial to bees in the western U.S. (DeBano 2006, Black
Providing
(Carvell 2002, Goulson 2010, McFreder- coast, such as B. crotchii in oak woodland, foraging efficiency (Goulson 2010). The the development of techniques for domes- et al. 2007). In the northwestern U.S., agricultural areas Artificial
ick and LeBuhn 2006, Rao and Stephen chaparral, and deserts and B. sitkensis and toxicity of specific pesticides is better tication. The actual pathogens implicated with blueberry (Vaccinium spp.) and red clover (Trifo- Nests for
2010). Some species can even prosper in B. caliginosus in cooler coastal climates. known for honey bees than bumble bees, are the protozoans Crithidia bombi and lium pratense) can support abundant populations of Bumble Bees
urban gardens and parks (McFrederick Elsewhere, isolated high alpine popula- but the available data suggest that toxicity Nosema bombi, although other pathogens several species of bumble bees (Rao and Stephen
and LeBuhn 2006, Matteson et al. 2008, tions of several species may disappear due to bumble bees is generally similar to that may also play important roles (Meeus et 2010). In any region, the keys are maintaining a Where nesting sites are
Matteson and Langellotto 2009). The to climate change. of honey bees (Alston and Tepedino 2000). al. 2011). Unfortunately, due to the lack reliable supply of nectar throughout the breeding limited, artificial nests
spread of Eurasian clovers (Trifolium) Phenology of queen emergence.— An application of pesticides to control of both stable populations of declining season, providing unplowed nesting habitats,
are an option to increase
and vetches (Vicia, Coronilla) has ben- Some authors suggest that species in spruce budworm in New Brunswick il- species in affected regions and informa- and limiting exposure to insecticides. Organic
efited some butterflies (Schweitzer 2006) lustrates the potential effects of pesticides tion about native pathogens, researchers farming practices may help promote bumble bumble bee populations
which queens become active later in
and presumably bumble bees as well. the season are at a disadvantage due to on bumble bees and other pollinators. In cannot directly test the effects of these bee populations, although other factors can (MacCulloch 2007, Kearns
Nevertheless, intensive agriculture has competition for nest sites and vulnerability this case, the pesticide application caused pathogens relative to other threats. confound research results (Winfree 2010). and Thomson 2001). The basic
caused local and regional declines in the to losses of food plants that are impor- blueberry crop losses due to reduced avail- Some bumble bee species can benefit from
Midwest as well as Europe (Grixti et al. ability of pollinators. In addition, reduced foraging in suburban and urban gardens, artificial nest is a box fitted with
tant in mid to late colony development
2009, Williams et al. 2009). The mismatch (Williams et al. 2009). In North America, pollination of nearby native species caused Conservation and (Frankie et al. 2009, McFrederick and a plastic pipe as an entrance
between the time scale of habitat loss nest competition is documented in urban a local wild berry shortage and conse- Management LeBuhn 2006). Manicured lawns and golf tunnel. The box can be made out
(before the mid 20th century) and rapidly areas of San Francisco where the early quently increased the number of birds courses with heavy pesticide use and de-
To complete their annual cycle, all bumble of wood (such as exterior grade
declining North American species (since B. vosnenskii apparently excludes the foraging on cultivated blueberries (Kevan void of flowers are among the least useful
bees need nesting habitat, flowers for nu-
the mid 1990s) suggests that habitat loss is later B. caliginosus and B. sitkensis from 1974). Bumble bee colonies can absorb the nesting and foraging habitats. plywood) or Styrofoam (such as
trition, and a place for queens to overwin-
unlikely to explain these declines (Grixti the limited supply of subterranean nest loss of a few workers to pesticides in sum- an old cooler). Dimensions vary
ter. They must also avoid lethal and sub- On more natural lands, management
et al. 2009). sites (McFrederick and LeBuhn 2006). mer, but worker loss can more seriously
lethal chemicals and pathogens. We know should focus on maintaining diverse as- but 8 x 8 x 6 inches (20 x 20 x 15
However, none of these species appear to impact colony survival in spring before
Climate change.—Although climate very little about overwintering needs, so semblages of primarily native flora, such
be declining globally, and there is no evi- colonies have built up significant numbers cm) is standard. The entrance
change has been suggested as a cause of the following summary of the growing that flowers would be constantly available
dence that phenology is linked to declines of workers (Goulson 2010). Additionally, hole should be ¼ inch (0.65 cm) in
declines and may be affecting bumble literature on bumble bee conservation and throughout the nesting season. In prairie
of bumble bees in North America where sub-lethal compounds may accumulate in
bees in some places, there is as of yet little management will focus on nesting and regions, restoration of native prairie diameter. The box can be placed
both early- and late-emerging species are the colony and affect the overall reproduc-
direct evidence that climate change is foraging needs. species and elimination of plowing, for ex- on the ground or 6-12 inches
among the five non-parasitic species that tive fitness of the colony. Species which
responsible for global declines of wide- ample along roadsides, can result in richer
are in severe decline. may be more vulnerable to pesticide use General habitat needs.—Bumble bees (15-30 cm) underground with the
spread species. In North America, most bumble bee faunas (Hopwood 2008).
include the above ground nesting spe- can be atypical targets for conservation
species occur (at least formerly) in a wide Tongue length and foraging ecol- entrance tube connecting the box
cies (e.g., subgenus Thoracobombus) and efforts. In contrast to many other rare The extent to which bumble bees use for-
array of climates, ranging through more ogy.—Bumble bees with long tongues are to the surface. Southern expo-
species with long colony cycles that can or endangered species, bumble bees may ests is a major knowledge gap for eastern
than ten degrees of latitude and some generally more specialized foragers. Al- accumulate toxins over the spring, sum- not require forest cover or even natural North American bumble bees, although sures, especially on a slight em-
from coast to coast. Moreover, most of though some authors have suggested that mer and fall. Pesticides likely contribute to habitats to maintain large and species-rich some species such as B. vagans seem to bankment, are best. Whatever
the North American species that have specialists (and therefore longer-tongued bumble bee declines in areas of intensive populations. Especially in eastern North be associated with wooded habitats (Colla
declined precipitously had large ranges. species) should be more likely to decline, agriculture, but are unlikely to be respon- America, a hayfield or powerline cut with the design or placement, the
and Dumesh 2010). Similarly, the effects of
Even B. affinis ranged from Maine to no such pattern has emerged in North box should contain insulation
sible for rapid, widespread declines (Colla plentiful wildflowers may be all that is standard forest management practices, such
Georgia and the Dakotas (Figure 3). America (Grixti et al. 2009, Williams et al. and Packer 2008, DeVore 2009). necessary for populations of a number of as thinning or controlled burning, on bumble in the form of upholsterer’s
Despite this large range, members of the 2009, Winfree 2010). One complication species (Russell et al. 2005). In fact, the bees are mostly undocumented. Opening forest
subgenus Bombus do seem to be some- with relating tongue length with forag- Pathogen spillover.—Currently, the cotton or polyester fiberfill.
endangered species Bombus affinis was canopies often allows more flowering of under-
what climatically restricted as they occur ing is that tongue length is individually most compelling hypothesis to explain Reported reasons for fail-
quite common in urban areas before its story plants, which should favor bumble bees (but
mostly at high elevations in southern parts variable with body size, whereas foraging rapid declines is the spillover of pathogens
collapse (Colla and Dumesh 2010). Re- see Nesting Habitat for the danger posed by fires). ure include ants, excess
of their ranges. Range breadth, combined preferences are largely learned (Kearns from managed to wild bumble bees (Colla
gardless of the region, management activi-
with high mobility and dispersal ability, and Thomson 2001). Direct measures of et al. 2006, Otterstatter and Thomson Food supply.—Observations of nest failure due to moisture, or mam-
ties should be aimed at improving flower
and the observed rapidity of declines seem foraging specialization, however, indicate 2008, Williams et al. 2009, Goulson 2010, food limitation highlight the need for a reliable nectar malian predators, so
availability and providing potential nest-
to argue against climate change as being a weak relationship with declines in Eu- Meeus et al. 2011). Field documenta- and pollen supply when bumble bees are active from
ing habitat (Blake et al. 2011). Specific managers should be
a major factor in recent dramatic declines. rope (Kleijn and Raemakers 2008). tion of pathogen spillover and related spring to late summer (Goulson 2010). In both natural
actions taken to achieve this objective will on the lookout for
However, more research is needed to modeling show waves of parasites and and anthropogenic habitats, multiple nectar plants with
Pesticides.—Direct exposure to pesticides vary depending upon whether manage-
further investigate this. pathogens spreading out from infested a succession of overlapping bloom periods are usually these problems.
can kill queen or worker bumble bees, ment is directed at agricultural, urban, or
commercial hives at multiple locations. required to satisfy this requirement. In some cases forag-
Species that may prove to be vulnerable and cause minor to lethal effects to larvae more natural lands.
Moreover, the timing of decline onset in ing habitats as well as plant species will vary seasonally. In
8 Conservation and Management of North American Bumble Bees NatureServe and the U.S. Forest Service 9You can also read
