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Biological Evaluation for

Western Bumble Bee Bombus occidentalis

(Greene, 1858)

Photo of Bombus occidentalis about to land on Camas Camassia quamash, July 30, 2013 at Butterfly Valley Botanical Area, Plumas National Forest Service

by Gary Zamzow, used by permission.

Written by: J. Furnish, May 2012; Updated September, 2013

Reviewed by: Stephanie Coppeto, Wildlife Biologist, LTBMU, April 2013

Adapted for: Lassen 15 Restoration Project by John Clark, Wildlife Biologist

Modoc National Forest, November 2015, Revised October 2016

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Distribution of the western bumble bee Bombus occidentalis in the PSW Region and North America

Bombus occidentalis currently occurs on many national forests throughout California (Figure 1) and in all

states adjacent to California (Figure 2). Historically, the species was broadly distributed across western

North America along the Pacific Coast and westward from Alaska to the Colorado Rocky Mountains

(Thorp and Shepard 2005, Koch et al. 2012). Historically, B. occidentalis was one of the most broadly

distributed bumble bee species in North America (Cameron et al. 2011). Currently, the western bumble

bee is experiencing severe declines in distribution and abundance due to a variety of factors including

diseases and loss of genetic diversity (Tommasi et al. 2004, Cameron et al. 2011, Koch et al. 2012).

Figure 1. Map of

PSW national

forests with

historic (prior to

2000) vs. recent

(post) collections

of the western

bumble bee

Bombus

occidentalis.

There are 116

collection records

for the western

bumble bee

Bombus

occidentalis on

nine national

forests of the PSW

Region (Hatfield

2012): Eldorado

(2), Klamath (15),

Lake Tahoe Basin

Management Unit

(7), Lassen (29),

Modoc (3), Plumas

(22), Shasta-Trinity

(25), Six Rivers (5)

and Tahoe (6).

There are only 25

collection records

from national

forest lands since

2000: 21 are on the

Lassen, three are

on the Plumas, and

one is on the Lake

Tahoe Basin

Management Unit

(Figure 1).

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Figure 2. Distribution of the western bumble bee Bombus occidentalis in the United States. At left,

individual collection sites are shown as yellow dots and green indicates the known range (reproduced

from Koch et al. 2012). At right, collection sites for Bombus occidentalis and other bumble bee species.

The orange portion of the circle indicates the proportion of the collection comprised of B. occidentalis.

The figure was modified from Cameron et al. (2011).

Bumble bees introduced from Europe for commercial pollination apparently carried a microsporidian

parasite, Nosema bombi, which has been introduced into native bumble bee populations. Highest

incidences of declining B. occidentalis populations are associated with highest infection rates with the

Nosema parasite, and the incidence of Nosema infection is significantly higher in the vicinity of

greenhouses that use imported bumble bees for pollination of commercial crops (Cameron et al. 2011).

Although the general distribution trend is steeply downward, especially in the west coast states, some

isolated populations in Oregon and the Rocky Mountains appear stable (Rao et al. 2011, Koch et al.

2012). The overall status of populations in the west is largely dependent on geographic region:

populations west of the Cascade and Sierra Nevada mountains are experiencing dire circumstances with

steeply declining numbers, while those to the east of this dividing line are more secure with relatively

unchanged population sizes. The reasons for these differences are not known.

Habitat & Life History

Management Considerations Within Suitable Habitat Areas Bumble bees are threatened by many kinds of habitat alterations that may fragment or reduce the

availability of flowers that produce the nectar and pollen they require, and decrease the number of

abandoned rodent burrows that provide nest and hibernation sites for queens. An example of a habitat

where Bombus occidentalis was recently observed in July 2013 is the Darlingtonia Bog at Butterfly

Valley Botanical Area on the Plumas National Forest (see Figure 3).

Major threats that alter landscapes and habitat required by bumble bees include agricultural and urban

development. Exposure to organophosphate, carbamate, pyrethroid and particularly neonicotinoid

insecticides has recently been identified as a major contributor to the decline of many pollinating bees,

including honey bees and bumble bees (Henry et al. 2012, Hopwood et al. 2012, Krupke et al. 2012). In

the absence of fire, native conifers encroach upon meadows, which also decreases foraging and nesting

habitat available for bumble bees.

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Figure 3. Photos of Darlingtonia bog habitat at Butterfly Valley Botanical Area, Plumas National

Forest, where Bombus occidentalis was observed in July 2013.

According to studies done in England (Goulson et al. 2008), grazing during the autumn and winter

months may provide excellent bumble bee habitat and prevent the accumulation of coarse grasses. Heavy

grazing and high forage utilization should be avoided since flowering plants providing necessary nectar

and pollen may become unavailable, particularly during the spring and summer when queens, workers

and males are all present and active.

The following account of bumble bee life history is summarized from Heinrich (1979) and illustrated in

Figure 4: Queens overwinter in the ground in abandoned rodent (i.e. mouse, chipmunk or vole) nests at

depths from 6-18 inches and typically emerge about mid-March. The queen then lays fertilized eggs and

nurtures a new generation. She first creates a thimble-sized and shaped wax honey pot, which she

provisions with nectar-moistened pollen for 8-10 individual first-generation workers when they hatch.

The larvae will receive all of the proteins, fats, vitamins and minerals necessary for growth and normal

development from pollen. Eventually all the larvae will spin a silk cocoon and pupate in the honey pot.

The workers that emerge will begin foraging and provisioning new honey pots as they are created to

accommodate additional recruits to the colony. Individuals emerging from fertilized eggs will become

workers that reach peak abundance during July and August. Foraging individuals are largely absent by the

end of September. Those that emerge from unfertilized eggs become males, which do not forage and only

serve the function of reproducing with newly emerged queens. During the season, a range of 50 to

hundreds of individuals may be produced depending on the quantity and quality of flowers available.

When the colony no longer produces workers, the old queen will eventually die and newly emerged

queens will mate with males and then disperse to found new colonies. During this extended flight that

may last for up to two weeks she may make several stops to examine the ground for a suitable burrow.

Mikkola (1984) reported that bumble bees may forage up to a distance of 80 km in Finland.

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Figure 4. Life cycle of a typical

bumble bee colony:

1. A queen emerges from

hibernation in spring and

finds a nest site, such as an

abandoned rodent burrow.

2. She creates wax pots to hold

nectar and pollen, on which

she lays and incubates her

eggs.

3. When her daughters emerge

as adults, they take over

foraging and other duties.

4. In autumn, the colony

produces new queens and

male bumble bees, which

leave to find mates. Newly

mated queens hibernate and

the rest of the bumble bees

die.

Figure reproduced from

Mader et al. (2011).

Unlike all other bees, bumble bees are large enough to be capable of thermoregulation, which allow them

to maintain their foraging activities for longer periods of the day, but also to occupy regions with more

extreme latitudes and temperatures compared to other bees (Heinrich 1979). Bumble bees may continue

to forage when temperatures are below freezing even in inclement weather (Heinrich (1979).

Queens end the year by locating a sheltering burrow, where they may spend the winter months under

cover. Where nesting habitat is scarce, bumble bee species having queens that emerge early (mid-March)

in the season like B. vosnesenskii which co-occurs with the later emerging B. occidentalis, may be able to

monopolize available nest sites and reduce the chances of success for bumble bee species emerging later. Western bumble bees have a short proboscis or tongue length relative to other co-occurring bumble bee

species, which restricts nectar gathering to flowers with short corolla lengths and limits the variety of

flower species it is able to exploit. Western bumble bees have been observed taking nectar from a variety

of flowering plants, including Aster spp., Brassica spp., Centaurea spp., Cimicifuga arizonica, Corydalis

caseana, Chrysothamnus spp., Cirsium spp., Cosmos spp., Dahlia spp., Delphinium nuttallianum, Erica

carnea, Erythronium grandiflorum, Foeniculum spp., Gaultheria shallon, Geranium spp., Gladiolus spp.,

Grindelia spp., Haplopappus spp., Hedysarum alpinum, Hypochoeris spp., Ipomopsis aggregata,

Lathyrus spp., Linaria vulgaris, Lotus spp., Lupinus monticola, Mentha spp., Medicago spp., Melilotus

spp., Mertensia ciliata, Monardella spp., Nama spp., Origanum spp., Orthocarpus spp., Pedicularis

capitata, P. kanei, and P. langsdorfii, P. groenlandica, Penstemon procerus, Phacelia spp., Prunus spp.,

Raphanus spp., Rhododendron spp., Salix spp., Salvia spp., Solidago spp., Symphoricarpos spp.,

Tanacetum spp., Taraxacum spp., Trifolium dasyphyllum, Trichostema spp., Trifolium spp. and Zea spp.

(Evans et al. 2008).

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Effects of the Alternatives

Key Indicators for Effects Analysis Include: continuous access to flowering plants from spring through autumn

potential nesting habitat, including rodent burrows

pesticide use during the project

Current Condition of the Habitat Factors in the Analysis Area:

Western bumble bee (Bombus occidentalis) was only recently added to the Modoc National Forest list of

Sensitive species on June 30, 2013. Casual sightings of bumble bees on the Warner Mountain Ranger

District have taken place, but identification of species and detailed observations have not yet been

undertaken by district personnel. For the purpose of this analysis, presence of the western bumble bee is

assumed, but unconfirmed, on the project area.

Of the 25,276 acres on the project area, 100 percent of the project area is composed of wildland habitats

for which western bumble bees are adapted.

No commercial crops, which employ domesticated pollinators, are grown adjacent to the project area,

thus limiting the potential for disease transfer to bumble bees as outlined by Furst et al. (2014).

Also, no herbicide or insecticide use is proposed as part of this project. The Modoc National Forest does

not use insecticides in routine forest and rangeland management.

General Discussion of the Range of Actions Proposed for this Project

The management actions proposed for this project include thinning of conifers, prescribed burning, road

construction and reconstruction, fuel break establishment and maintenance, planting, and weir repair (see

Proposed Action in the Lassen 15 Restoration Project Environmental Assessment).

Vegetation Management

General discussion

The plant and animal communities present on the project area evolved with wildfire. Therefore,

disturbances to vegetation, particularly the understory vegetation, were relatively frequent natural

occurrences. Wild fire typically removes much of the existing understory vegetation during the year it

occurs, followed by years of no fire during which vegetation can regrow and recover.

Alternative 1 - (Proposed Action)

Direct and Indirect Effects: There are many potential beneficial impacts to western bumble bee habitat by implementation of

alternative 1. Opening forest canopies through application of thinning and prescribed burning is expected

to benefit flowering plants by allowing more sunlight to reach the forest floor, reducing competition from

trees for water and nutrients, and reducing the quantity of needle cast and duff on the soil surface.

Nutrients released by prescribed burning may fertilize flowering plants, resulting in increased floral

resources available to bumble bees. Also, ground disturbance caused by thinning, road reconstruction,

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and fuel break activities would probably favor pioneering species of flowering plants, thus providing

additional floral resources for western bumble bees.

Densities of burrowing rodents in the project area are expected to respond positively to increased

abundance of understory plants in the years following thinning and prescribed burning. Due to reduced

canopy cover, needle cast and reduced competition for sunlight, soil moisture and nutrients, understory

plants including grasses and flowering plants are expected to provide increased food supplies for rodents.

As a result, the number of rodent burrows which provide potential nesting sites for bumble bees should

increase.

Planting activities would have a minimal effect on floral resources, due to limited amount of ground

disturbance associated with the activity.

Road re-construction would have no effect on floral resources since there are no flowers growing within

the road prisms. Road construction would have a minor effect to floral resources due to limited amount

of disturbance.

The management activities proposed for this project and the reasonably foreseeable activities on adjacent

lands would follow sequences of short-term disturbances followed by years of no impacts. This would be

similar to the sequence of natural fire impacts.

Potential negative impacts to western bumble bee habitat would include: Some flowering plants may be

damaged or killed during thinning, prescribed burning, road reconstruction and fuel break establishment

and maintenance. However, these negative impacts would be limited to the growing season in which the

treatment activities take place. In subsequent growing seasons, flowering plants in the impacted areas

would recover, reoccupy disturbed areas and invade sites previously dominated by trees or other species.

Cumulative Effects of Alternative 1 (Action Alternative):

Past and present activities affecting the project area include: grazing by cattle, timber harvest, forest

thinning, prescribed burning, fuelwood gathering, dispersed recreation, suppression of wildfires, and

obsidian mining (Table 1). The cumulative effects analysis area includes the project area and a 3-mile

buffer around the project area. The cumulative effects listed date from 2004. Future impacts are

anticipated during the coming decade.

Table 1. Forest management activities for the Lassen 15 Restoration Project Area from 2004 through

most recent reporting period.

Year Activities Acres 2004 Prescribed Burning 434 2005 Prescribed Burning 486 2006 Prescribed Burning 139 2007 Thinning/Tree Planting 214 2008 Thinning 12 2010 Tree Planting 25 2011 Thinning 677 Ongoing (all years) Cattle Grazing 25,276 Ongoing (all years) Obsidian Mining; Mine Protection & Safety 31

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Vegetation Management - Timber harvest and prescribed burning have occurred on the project area,

which consists of ponderosa pine, eastside pine, white fir, and mixed conifer stands. Past timber harvest

and prescribed burning appeared to release understory vegetation, especially Ceanothus velutinus.

According to various websites, bees appear to use the flowers of this species. Therefore, timber harvest

and burning have increased foraging opportunities for bees within the analysis area.

It is anticipated that the thinning and prescribed burning proposed in the Lassen 15 EA would cause the

same long-term increase in understory plants, due to decreased competition from trees for sunlight, soil

nutrients and soil moisture. Although short-term disruption of floral resources could result from project

activities, recovery would generally occur within one growing season.

Firewood cutting is not anticipated to affect bumble bees, since they do not use snags for nesting. In

addition, fuelwood cutting on the project area is limited by distance from population centers and therefore

is discountable.

Thinning and prescribed burning have been proposed to make the project area more suited to the

beneficial effects of natural fire and more resistant to wildfire, insect outbreaks and disease. The proposed

treatments and the potential return of natural fire would stimulate floral resources important to bumble

bees. Therefore, vegetation management activities proposed under the Lassen 15 EA are expected to

have beneficial cumulative effects.

Fire Management – A combination of factors including fire suppression has allowed increased stocking

of conifers on the project area. Consequently, there is a decrease in the floral resources available to

bumble bees. Therefore, fire suppression has had negative effects on potential bumble bee habitat.

However, the forest restoration measures proposed in this project would help reverse the decrease in floral

resources. Therefore, the activities proposed in the Lassen 15 EA would have beneficial cumulative

effects with respect to fire suppression.

Grazing - Seasonal livestock grazing permitted under Forest Standards results in minor disturbances to

the shrub canopy layer and reduction in herbaceous materials. The impact on bee foraging opportunities

from managed, rotational grazing on the analysis area has not been quantified, but is unlikely to limit the

distribution of bumble bees. Cattle grazing on significant portions of the project area is very light or non-

existent, due to dense brush and difficult terrain. Bumble bees forage on the flowers of various woody

plants; thus, the dense stands of shrubs on the project area would be available as foraging opportunities

for bees in addition to herbaceous plants. Therefore, livestock grazing would provide no negative

cumulative impacts with respect to the implementation of activities proposed in the Lassen 15 EA.

Special Uses - Obsidian mining is permitted under the Warner Mountain Obsidian Management Plan.

Abundant obsidian in the project area has attracted both commercial and recreational miners. One

obsidian mine, the Lassen Creek Rainbow Mine (Rainbow), is located within the Lassen 15 Project

area. Authorized mining activity occurs from May 1st to November 1st annually. Mining activity is

a combination of commercial and personal use within the specifically delineated mining area. Excavation

and removal of obsidian is done only with the use of non-mechanized hand tools. Historically, the

Rainbow has 2 to 3 commercial operators that would account for up to 3 vehicles and perhaps 6

individuals for days at a time and periodically throughout the authorized period. Because Rainbow is on a

major travel way to Lassen Creek Campground, recreational/personal use obsidian collection can account

for several small family groups at the mine during any summer week.

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Three other obsidian mines are located within 3 miles of the Lassen 15 Restoration Project analysis area.

They are the: Middle Fork Davis Creek Mine, Obsidian Needles Mine and the Pink Lady Mine. All the

obsidian mines operate under the Warner Mountain Obsidian Management [Plan], which authorizes

obsidian mining, as well as resource and safety protection measures that can be used at the mine sites.

Obsidian mining has little or no impact on existing tree canopies, but introduces human presence and

disturbance to the project area. However, the obsidian mines are small in size accounting for only 14.8

acres (less than 1/10th of 1 percent) of the 25,276 acres on the project area. There is no anticipated

decrease in area for potential burrows and no significant decrease in floral resources from mining.

Therefore, there are no cumulative effects from Special Uses with respect to the Lassen 15 EA.

Recreation - Dispersed recreation is focused along Lassen Creek and at the obsidian mines. Due to the

low use of meadows and other habitats rich in flowers, recreation would not contribute to cumulative

negative effects to potential western bumble bee habitat.

Noxious Weed Management - Invasive plants may be treated with either herbicide or hand grubbing

according to the Modoc National Forest Noxious Weed Treatment Project standards and guidelines;

however, no herbicide treatment is planned currently within the project area. Treatments are typically

small in size and carefully prescribed to minimize potential impacts. Some noxious weeds are used as

food sources by bumble bees. Conversely, the effect of not treating the habitat could cause a significant

decrease in the amount of native floral resources for bumble bees. Although there may be nominal

negative impacts to floral resources by the treatment of noxious weeds, the magnitude would depend on

the species of noxious weeds and the plants that replaced them after treatment.

Road Management - Road designation and maintenance activities occur within road prisms, which do

not have flowers and are not used for burrowing. Therefore, road management is not expected to affect

bumble bee habitat.

Climate Change - Bumble bees are generalist foragers (The Xerces Society, 2015). As such, they use a

wide variety of floral resources over the course of a growing season. This ability would likely allow them

to adapt to changes in floral resources that may take place as a result of climate change.

To summarize, the contribution of Alternative 1 to cumulative effects to the western bumble bee

would be low considering all of the past, present and foreseeable actions in and adjacent to the

Lassen 15 Restoration Project area.

Alternative 2 – (No Action) Direct and Indirect Effects: Potential negative impacts to western bumble bee habitat of Alternative 2 are as follows. There would be

a continued increase in tree canopy cover in the absence of thinning and prescribed fire. A combination

of this and the inclusion of fire suppression has allowed increased stocking of conifers on the project area.

Consequently, there is a decrease in the floral resources available to bumble bees.

Also, there would be no stimulation of understory vegetation without proposed thinning and burning to

release nutrients.

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Potential beneficial impacts to western bumble bee habitat of this alternative would include no damage to

floral resources due to thinning, prescribed burning and fuel break establishment during the season of

treatment.

Cumulative Effects of Alternative 2 (No Action Alternative):

Past and present activities affecting the project area include: livestock grazing, timber harvest, forest

thinning, prescribed burning, fuelwood gathering, dispersed recreation, suppression of wildfires, and

obsidian mining. The same cumulative effects analysis area and timeframe used for the Action

Alternative was used for this Alternative as well.

No Lassen 15 Restoration Project treatments would take place resulting in no beneficial impacts to flower

resources within the project area.

In the absence of thinning and prescribed burning, there potentially would be an increase in the potential

for wild fire to occur within the analysis area. Continued fire suppression would also allow for increased

tree canopy, which would reduce understory flowering plants.

If a subsequent wild fire did occur, there would be a short term decrease in floral resources until plant re-

growth occurred, long-term there would be a substantial increase in flowering plants. That would in turn

provide potential increased suitable bumble bee habitat.

Firewood collection would have no effect on bees, since they do not use snags for nesting.

Due to the light grazing over the majority of the project area and the presence of dense brush (while

serving to impede cattle movement provides foraging opportunities), it is anticipated that continued

grazing would not have a negative cumulative effect with respect to the No Action Alternative.

Obsidian mining, recreation, road maintenance, and noxious weed treatments would continue to have

minimal impacts to bumble bees, due to the localized nature of all of these activities.

DETERMINATIONS

It is my determination that the proposed actions for the Lassen 15 Restoration Project and the no-

action alternative “May affect individuals, but is not likely to result in a trend towards federal

listing or loss of species viability” for western bumble bee.

Literature Cited

Alaux, C., J. Brunet, C. Dussaubat, F. Mondet, S. Tchamitchan, M. Cousin, J. Brillard, A. Baldy, L.P.

Belzunces and Y. Le Conte. 2010. Interactions between Nosema microspores and a neonicotinoid

weaken honeybees (Apis mellifera). Environmental Microbiology 12: 774–78.

Cameron, S.A., J.D. Lozier, J.P. Strange, J.B. Koch, N. Cordes, L.F. Solter and T.L. Griswold. 2011.

Patterns of widespread decline in North American bumble bees. Proceedings of the National Academy

of Sciences 108:662-667. See http://www.pnas.org/content/108/2/662.full.pdf+html .

Carvell, C., W.R. Meek, R.F. Pywell, D. Goulson, M. Nowakowski. 2007. Comparing the efficacy of

agri-environment schemes to enhance bumble bee abundance and diversity on arable field margins.

Journal of Applied Ecology, 44:29-40.

11

Dupont, Y.L, C. Damgaard, V. Simonsen. 2011. Quantitative Historical Change in Bumblebee (Bombus

spp.) Assemblages of Red Clover Fields. PuPLoS One Volumbe 6: Issue 9. Available at

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0025172

Evans, E., R. Thorp, S. Jepsen and S.H. Black. 2008. Status Review of Three Formerly Common Species

of Bumble Bee in the Subgenus Bombus: Bombus affinis (the rusty patched bumble bee), B. terricola

(the yellowbanded bumble bee), and B. occidentalis (the western bumble bee). The Xerces society,

Portland, OR. Available at

http://www.xerces.org/wp-content/uploads/2009/03/xerces_2008_bombus_status_review.pdf

Fürst, M.A., McMahon, D.P., Osborne, J.L., Paxton, R.J. & Brown, M.J.F., 2014. Disease associations

between honeybees and bumblebees as a threat to wild pollinators. Nature, 506, 364–366.

Goulson, D., G.C. Lye and B. Darvill. 2008. Decline and Conservation of Bumble Bees. Annual Review

of Entomology 53:191–208

Hatfield, R. 2012. Records of western and Franklin’s bumble bees in the western United States. Database

records provided by the Xerces Society, Portland, OR on 2/29/12.

Heinrich, B. 1979. Bumblebee Economics. Harvard University Press, Cambridge, MA. 245 pp.

Henry,M., M. Beguin, F. Requier, O. Rollin, J. Odoux, P. Aupinel, J. Aptel, S. Tchamitchian and A.

Decourtye. 2012. A Common Pesticide Decreases Foraging Success and Survival in Honey Bees.

SciencExpress available at

http://www.sciencemag.org/content/early/2012/03/28/science.1215039.full.pdf

Hopwood, J., M. Vaughan, M. Shepherd, D. Biddinger, E. Mader, S. Hoffman Black and C. Mazzacano.

2012. Are Neonicotinoids Killing Bees? A Review of Research into the Effects of Neonicotinoid

Insecticides on Bees, with Recommendations for Action. Xerces Society, Portland, OR. Available at

http://www.xerces.org/wp-content/uploads/2012/03/Are-Neonicotinoids-Killing-Bees_Xerces-

Society1.pdf .

Koch, J., J. Strange and P. Williams. 2012. Bumble Bees of the Western United States. U.S. Forest

Service and the Pollinator Partnership, Washington, D.C. 144 pp.

Kreyer, D., A. Oed, K. Walther-Hellwig and R. Frankl. 2004. Are forests potential landscape barriers for

foraging bumblebees? Landscape scale experiments with Bombus terrestris agg. and Bombus

pascuorum (Hymenoptera, Apidae). Biological Conservation 116 :111–118.

Krupke, C.H., G.J. Hunt, B.D. Eitzer, G. Andino and K. Given. 2012. Multiple routes of pesticide

exposure for honey bees living near agricultural fields. PLoS ONE 7(1):e29268.

doi:10.1371/journal.pone.0029268.

Mader, E., M. Shepherd, M. Vaughan, S. Black and G. LeBuhn. 2011. Attracting Native Pollinators:

Protecting North America's Bees and Butterflies. The Xerces Society Guide to Conserving North

American Bees and Butterflies and Their Habitat. Storey Publishing, North Adams, MA. 371 pp.

McFrederick QS, Le Buhn G. 2006. Are urban parks refuges for bumble bees? Biol. Conserv. 129:372–

382.

Mikkola, K. 1984. Migration of wasp and bumblebee queens across the Gulf of Finland (Hymenoptera:

Vespidae and Apidae). Notulae Entomologicae 64: 125-128.

Osborne, J.L., A.P. Martin, N.L. Carreck, J.L. Swain, M.E. Knight, D. Goulson, R.J. Hale and R.A.

Sanderson. 2008. Bumblebee flight distances in relation to the forage landscape. Journal of Animal

Ecology 77:406–415.

Rao,S., W.P. Stephen, C. Kimoto and S.J. DeBano. 2011. The Status of the ‘Red-Listed’ Bombus

occidentalis (Hymenoptera: Apiformes) in Northeastern Oregon. Northwest Science 85: 64-67.

Saab, V. A. and H. D. W. Powell. 2005. Fire and avian ecology in North America: Process influencing

pattern. Studies in Avian Biology 30:1-13.

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.

The Xerces Society, 2015. Bumble bees: western bumble bee (Bombus occidentalis).

http://www.xerces.org/western-bumble-bee/. Accessed 11-20-2015.

12

Thorp, R. W., and M. D. Shepherd. 2005. Profile: Subgenus Bombus. In Shepherd, M. D., D. M.

Vaughan, and S. H. Black (Eds). Red List of Pollinator Insects of North America. The Xerces Society

for Invertebrate Conservation, Portland, OR.

Tommasi, D., A. Miro, H. A. Higo and M. L. Winston. 2004. Bee diversity and abundance in an urban

setting. The Canadian Entomologist 136: 851–869.

Williams, P.H. and J.L. Osborne. 2009. Bumblebee vulnerability and conservation world-wide.

Apidologie 40:367–387.