Artificial Domicile Use by Bumble Bees (Bombus; Hymenoptera: Apidae) in Ontario, Canada

Abstract

Bumble bees are an important group of pollinating insects that are of increasing conservation concern due to relatively recent and dramatic species-specific declines. Nesting ecology can vary significantly between species, and nest site selection may be affected by many factors, including heredity, individual experience, and habitat availability. Data on bumble bee nesting ecology are inherently difficult to collect in the wild as nests are often cryptic. Artificial domiciles (nest boxes) can be a useful tool for gathering information on species-specific nesting behavior to inform conservation management of native pollinator populations. The aim of this study was to examine the use of three different domicile designs for monitoring bumble bees: aboveground, underground, and false underground, while collecting information on occupying species identity and richness to compare with sampling with traditional netting survey methods. Across Ontario, the majority of sites had at least one domicile occupied, with the aboveground installation method proving most successful whereas no false-underground domiciles were occupied. Occupied domiciles appeared to preferentially sample certain species compared to netting surveys, and rarefied species richness of both methods was similar. Given that some bumble bees did occupy artificial domiciles, and species richness relative to sample size was high, with further refinement, this method may be useful for bumble bee research and monitoring: filling in nesting ecology knowledge gaps and potentially as a conservation management tool.

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Artificial Domicile Use by Bumble Bees (Bombus;
Hymenoptera: Apidae) in Ontario,Canada
SarahA. Johnson,1,2,6, MeaganM. Tompkins,3 Hayley Tompkins,2,4 and SheilaR. Colla5
1Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada, 2Wildlife
Preservation Canada, Native Pollinator Initiative, 5420 Highway 6 North, Guelph, ON N1H 6J2, Canada, 3Department of Biology, York
University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada, 4School of Environmental Sciences, University of Guelph, 50 Stone
Road East, Guelph, ON N1G 2W1, Canada, 5Faculty of Environmental Studies, York University, 4700 Keele Street, Toronto, ON M3J
1P3, Canada, and 6Corresponding author, e-mail: sa_johnson@sfu.ca
Subject Editor: Guy Bloch
Received 31 August, 2018; Editorial decision 19 December, 2018
Abstract
Bumble bees are an important group of pollinating insects that are of increasing conservation concern due to
relatively recent and dramatic species-specific declines. Nesting ecology can vary significantly between species, and
nest site selection may be affected by many factors, including heredity, individual experience, and habitat availability.
Data on bumble bee nesting ecology are inherently difficult to collect in the wild as nests are often cryptic. Artificial
domiciles (nest boxes) can be a useful tool for gathering information on species-specific nesting behavior to inform
conservation management of native pollinator populations. The aim of this study was to examine the use of three
different domicile designs for monitoring bumble bees: aboveground, underground, and false underground, while
collecting information on occupying species identity and richness to compare with sampling with traditional netting
survey methods. Across Ontario, the majority of sites had at least one domicile occupied, with the aboveground
installation method proving most successful whereas no false-underground domiciles were occupied. Occupied
domiciles appeared to preferentially sample certain species compared to netting surveys, and rarefied species
richness of both methods was similar. Given that some bumble bees did occupy artificial domiciles, and species
richness relative to sample size was high, with further refinement, this method may be useful for bumble bee research
and monitoring: filling in nesting ecology knowledge gaps and potentially as a conservation management tool.
Key words: domicile, conservation, methodology, diversity, colony
Bumble bees [Bombus (Latreille)] are ecologically and economically
important due to their key role pollinating native and agricultural
plants (Losey and Vaughan 2006, James and Pitts-Singer 2008, Potts
etal. 2010). Growing evidence suggests multiple species are declin-
ing (Colla and Packer 2008, Goulson etal. 2008, Grixti etal. 2009,
Cameron et al. 2011), and their unique colony cycle and habitat
requirements may be contributing factors (Bartomeus etal. 2013).
However, bumble bee nesting ecology is poorly understood; nests
are often inconspicuous, making large surveys difcult (Kells and
Goulson 2003, Lye etal. 2011). Developing reliable methods for
studying nesting ecology is critical for conservation management.
Articial domiciles have potential as tools to investigate bumble
bee life history. With domiciles, colonies can be monitored to
examine nesting behavior, foraging, sociality, habitat requirements,
and response to environmental stressors. Domiciles may also provide
a method of augmenting populations, requiring research to under-
stand their capacity to support declining species.
Bumble bee domestication and rearing for crop pollination and
research has a long history, including the development of in situ
(domiciles) and ex situ (lab rearing of spring-caught queens) meth-
odologies (Sladen 1912, Velthuis and Van Doorn 2006). Domicile
use began in early-20th-century England (Sladen 1912) and later
expanded through the United Kingdom (Lye etal. 2011) and into New
Zealand (e.g., Donovan and Wier 1978) and North America (e.g.,
Frison 1926). Historically, occupancy ranged from <10% (Macfarlane
1974) to between 20 and 50% (Sladen 1912, Frison 1926, Fye and
Medler 1954, Donovan and Wier 1978, Richards 1978). Recent use of
domiciles has been less successful, with occupancy typically between 0
and 10% (Barron etal. 2000, Lye etal. 2011). Research design is vari-
able, but occupation by a total of 7 European bumble bees (5 common
species and 2 rare species), all 4 New Zealand species (introduced),
and 21 North American species (including the declining Bombus ter-
ricola (Kirby), Bombus occidentalis (Greene), and Bombus pensylvan-
icus (De Geer)) has been observed.
Assessing whether domiciles are useful for conservation manage-
ment requires determining whether the local bumble bee commu-
nity uses them unbiasedly. To date, efcacy investigations have not
addressed this, and recent studies in North America are lacking. We
Journal of Insect Science, (2019) 19(1): 7; 1–5
doi: 10.1093/jisesa/iey139
Short Communication

explore the effectiveness of three domicile installation methods and
contrast occupying species to netting surveys in Ontario, Canada.
Quantifying use will help determine the future value of domiciles for
bumble bee conservation.
Materials and Methods
Domiciles were installed at 15 sites throughout south-central
Ontario between 1 and 15 April 2017 (Fig. 1). Fourteen sites were
‘type 1’, containing underground and aboveground domiciles, and
one site was ‘type 2’, containing two sizes of false-underground (cov-
ered with vegetation at ground level) domiciles across ve subsites.
Netting surveys were conducted at 33 sites throughout the same
regions to quantify the surrounding community (Fig. 1). Bumble
bees were not always netted at the same locations as domiciles, but
minimum one survey was conducted within 20 km from eachsite.
Domiciles were constructed using untreated ¾” spruce plywood
(West Fraser wood products) and lined with upholsterers’ cotton,
based on previously successful designs (Hobbs etal. 1960). Canopy
cover (densiometer) and entrance aspect were quantied for every
domicile.
At type 1 sites, seven underground and seven aboveground dom-
iciles (measuring 18 × 18× 19 cm; Fig. 2a and b) were deployed
(=196). Underground domiciles were installed on slopes and
tted with 20-cm PVC pipe entrances (20 mm external diame-
ter). Aboveground domiciles were mounted to trees (70–150 cm
in height). Lids were covered with waterproong plastic sheeting
(Munn 1998). Each domicile was 3- to 10-m distance from its near-
est neighbor.
At the type 2 site, 150 false-underground domiciles were de-
ployed on the ground, obscured by vegetation: 75 small (15× 15×
15cm) and 75 large (30× 15× 15cm; Fig. 2c), all with 30-cm pipe
entrances. Five subsites were chosen based on queen observations
and habitat type. Thirty domiciles were installed per subsite, min-
imum 2 m apart. Large and small domiciles were paired.
All sites were visited before collection to assess colony progres-
sion, and domiciles were removed after senescence. Domiciles with
signs of bumble bee presence (e.g., dead bumble bees, wax structures
like brood cells, nectar pots) were scored as occupied. For estab-
lished colonies, counted brood cells were a proxy for colony success.
Bumble bee netting data from 33 sites between 24 April 2017
and 8 June 2017 (n=1,221 individuals) were used to measure local
community composition. Sites were surveyed 0.5–4 h, depending
on bumble bee abundance, and 1–146 bees were sampled per visit
(mean 37 bees per site). Only queens were included to ensure rele-
vant comparison to nest-founding individuals. All individuals were
temporarily collected, identied, and released. Only condently
identied individuals were analyzed.
Fig. 1. Map of 15 domicile and 33 netting study sites located throughout south-central Ontario, Canada. On the left, large-scale site locations and types are
displayed, and on the right, smaller insets show domicile arrangement for each site type.
2 Journal of Insect Science, 2019, Vol. 19, No. 7

To test whether species in domiciles differed from the netted
community, we generated a null distribution for domicile species
occupancy (using R version 3.4.3 (R Core Team 2018)). This dis-
tribution was constructed by repeatedly lling occupied domiciles
with bumble bees sampled probabilistically from the netting data-
set. We employed three spatial models: 1)all observations in the
netted dataset sampled with equal probability to ll each dom-
icile, 2)bees only sampled within a specied distance, and 3) a
netted bee’s sample probability was inversely proportional to that
observation’s distance. These models yielded the same conclusions,
so we only present the most conservative (inverse distance). We
ranked bee species according to their probability of occupying
each domicile (domicile-specic ranks), such that the species most
likely to occupy a domicile was assigned rank 1, the species sec-
ond most likely assigned rank 2, and so on. We then calculated
the mean rank of the species collection for each of our randomly
sampled sets of occupants to produce the null distribution of mean
rank of occupants. The proportion of mean ranks that are more
extreme than the mean rank of the species that actually occupied
domiciles provides an empirical P-value.
To relate species richness of domicile and netting samples, netting
sample size was rareed to the number of occupied domiciles using
the ‘rarefy’ function in package ‘vegan’ (Oksanen etal. 2018).
Results
Of the 346 domiciles installed, 17 (4.9%) were occupied by bumble
bees; type 1 sites had an occupation rate of 8.6%, and the type 2 site
was unsuccessful. Occupied domiciles were distributed unequally
across 60% of all sites (Fig. 3). Four of 98 (4.1%) underground
and 13 of 98 (13.3%) aboveground domiciles were occupied. The
highest site-level occupation rate was 36% (Table 1). Asummary of
site-level mean habitat variables per domicile is included in Table 1,
though low sample size precluded comparison of unoccupied and
occupied domiciles. The mean entrance aspect for occupied domi-
ciles was 55° (NE) and canopy cover was72%.
Of the 17 occupied domiciles, only 13 contained remains that
were identiable to species. Nine showed signs of parasitism by
Achroia grisella (Lepidoptera: Pyralidae) Fabricius, where larvae
completely destroyed wax remains preventing the counting of
brood cells in eight of those nine. Of the preserved nests, colonies
ranged dramatically in size from 4 to 782 brood cells. Six different
species were observed, including Bombus bimaculatus Cresson
(n=2), Bombus griseocollis De Geer (n=2), Bombus impatiens
Cresson (n = 1), Bombus perplexus Cresson (n =5), Bombus
rufocinctus Cresson (n=2), and Bombus ternarius Say (n= 1).
Most species inhabited exclusively aboveground (B.griseocollis,
B.perplexus, and B. rufocinctus) or underground (B.impatiens
and B. ternarius) domiciles with one exception—B.bimaculatus
occupied one ofeach.
Species that occupied domiciles were on average signicantly
locally rarer than expected by distance-weighted netted observations
(P<0.001, Fig. 4). This difference appears to be driven by the over-
representation of B. perplexus, B. griseocollis, and B. rufocinctus
and underrepresentation of B.bimaculatus, B.impatiens, and B.ter-
narius in domiciles compared with their likelihood of selection based
on distance-weighted abundance (Fig. 4). When rareed to a sample
size equal to the number of occupied domiciles (n=17), species rich-
ness for queen netting surveys in domicile regions was adjusted from
9 to 4.71 species ± 1.03 (SE), indicating that domiciles captured a
community at least as rich (n =6 species) as netting, despite low
overall occupancy.
Fig. 2. Photographs of each domicile installation method: (a) underground domicile before complete burial, (b) aboveground strapped to tree, and (c) false-
underground hidden in vegetation.
012345
Domiciles occupied (n)
Site frequency (n)
0123456
Fig. 3. Number of domiciles occupied per site displayed as a site-level
frequency histogram, indicating how often an individual site contained from
zero to five occupied domiciles.
Journal of Insect Science, 2019, Vol. 19, No. 7 3

Discussion
Domicile occupancy rate was low for all sites, but success per type and
installation method varied signicantly. Given the range by installa-
tion method from 0% (false underground) to 13% (aboveground)
and from 0 to 36% between sites, many factors are probably inu-
encing the establishment of colonies. Aboveground domiciles were
our most successful, though installation method does not reliably
predict occupation success: aboveground and underground domi-
ciles have been both successful (20–100%, Sladen 1912, Fye and
Medler 1954, Richards 1978) and comparatively unsuccessful
(0–14%, Hobbs etal. 1960, Barron etal. 2000, Lye etal. 2011). In
this study, both underground and false-underground domiciles were
often subject to improper drainage, and entrances were frequently
blocked by soil/vegetation. It is difcult to disentangle site-level ef-
fects from installation method effects for type 2 subsites containing
all 150 empty false-underground domiciles—false-underground
domiciles too have been both successful and unsuccessful in past
work (0–43%, Hobbs etal. 1960, Macfarlane 1974, Richards 1978).
Domicile design has also been historically variable and does not ap-
pear associated with success rate—metal coffee tins (Sladen 1912,
Frison 1926), stock lumber, clay (Fye and Medler 1954, Hobbs etal.
1960, Macfarlane 1974), and plywood (Richards 1978, Barron etal.
2000, Lye etal. 2011) constructions, most often cubic and similar
dimensions, have all been both successful and unsuccessful at at-
tracting queens.
No previous domicile studies have attempted to make diversity
comparisons to alternate sampling methods. We found that com-
munity-level local species abundance from netting surveys was not
strongly predictive of species found in domiciles. Several occupying
species were observed frequently in domiciles but rarely in nets, sug-
gesting the potential inuence of species-specic nesting preferences
or a species-level likelihood for acceptance of articial nesting struc-
tures. Bombus perplexus, our most common occupant, is known to
accept manmade structures and has been previously observed using
Proportion of domiciles
B. bimaculatus
B. impatiens
B. ter
narius
B. per
plexus
B. vagans
B. ter
ricola
B. griseocollis
B. borealis
B.
ruf
ocinctus
B. citrinus
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Null distribution
Tr ue occupancy
Fig. 4. Comparison of bumble bee species observed in occupied boxes versus the null distribution as sampled from netting surveys. Proportion is calculated
from n=13 for true occupancy and n=130,000 (13 occupied domiciles generated over 10,000 runs) for the null distribution.
Table 1. Bumble bee domicile occupation summary by site, including per-domicile habitat variable averages.
Sites Latitude Longitude Occupied domiciles Canopy cover (mean) Aspect (mean)
1 (Awenda Provincial Park) 44.824741 −79.987468 2 A, 3 U 68% 230° (SW)
2 46.38699 −81.37376 3 A 25% 150° (SSE)
3 43.55766 −80.09742 2 A 97% 0° (N)
4 (Inverhuron Provincial Park) 44.29961 −81.58835 2 A 93%w 150° (SSE)
5 (Guelph Lake Conservation Area) 43.60075 −80.25816 1 A 73% 260° (WSW)
6 42.88733 −80.26023 1 A 61% 15° (NNE)
7 42.84967 −80.2035 1 A 50% 125° (ESE)
8 (Fairbank Provincial Park) 46.46868 −81.43967 1 A 90% 40° (NE)
9 (Windy Lake Provincial Park) 46.620813 −81.456546 1 U 48% 240° (WSW)
10 42.84971 −80.38653 0 A, U 76% 40° (NE)
11 (Pinery Provincial Park) 43.24315 −81.84042 0 A, U 90% 15° (NNE)
12 (Halfway Lake Provincial Park) 46.90849 −81.63226 0 A, U 57% 275° (W)
13 46.68774 −80.91743 0 A, U 50% 105° (ESE)
14 46.57001 −80.84492 0 A, U 34% 185° (SSW)
15 (Kofer Scientic Reserve) 44.029596 −79.53159 0 F 13% 150° (SSE)
Occupied domiciles by installation method: A(aboveground), U (underground), and F (false underground).
4 Journal of Insect Science, 2019, Vol. 19, No. 7

domiciles (Farmer 2014; S.Johnson, unpublished data). Bombus hyp-
norum (Linnaeus), a European species closely related to B.perplexus
(Hines 2008), occasionally inhabits bird boxes (Lye etal. 2011), indi-
cating a potential subgenus-level component to this overrepresenta-
tion. If domiciles are species biased, application for nesting structures
in life-history research in the occupying species will still be invaluable.
Previous North American studies have domicile occupation by
21 of 46 (45.6%) species (Frison 1926, Fye and Medler 1954, Hobbs
etal. 1960, Hobbs 1967, MacFarlane 1974, Richards 1978). Each
of our occupants has previously accepted domiciles, but three never
before in Ontario (B.bimaculatus, B.griseocollis, and B.ternarius;
Macfarlane 1974). Species richness in domiciles was at least as
diverse as rareed netting richness, suggesting that domiciles could
be valuable for collecting data for a wide range of bumble bees,
pending increased occupation.
It is difcult to compare success between studies due to sub-
stantial temporal (Sladen 1912 to current), spatial (Europe, New
Zealand, and North America), and methodological (design and
installation) variation. Factors such as landscape disturbance lev-
els, interactions between local bumble bee, oral, and natural nest
site abundance, nesting preferences, and domicile design (Barron
etal. 2000, Lye etal. 2011) are probably all important. Given our
observed levels of between-site variation, between-method variation,
and the tendency of overrepresentation of certain species compared
with netting, site-level characteristics and species preferences may
strongly inuence occupation rates in Ontario. To disentangle these
effects, manipulative experiments are probably necessary.
Our ndings suggest domiciles have utility as a tool for ecolog-
ical study if occupation rates can be increased. Given the overrep-
resentation of certain species that accept domiciles in Ontario, care
should be taken when considering application to at-risk species con-
servation management, or for examining bumble bee communities
independent of other survey methods. Recent North American dom-
icile research is lacking, and in light of species declines, more work
is needed to assess whether reduced modern occupancy (e.g., Barron
etal. 2000, Lye etal. 2011) is associated with conservation status.
Given the potential value of using domiciles to ll knowledge gaps
in bumble bee nesting behavior and colony development, additional
evaluation of different installation methods will be valuable for clar-
ifying inuences on per-species occupation.
Acknowledgments
We thank Ralph Cartar for study design and analysis guidance, Leithen
M’Gonigle for assistance with analysis conception and programming, the
Ontario Ministry of Natural Resources and Forestry (OMNRF) and Kofer
Scientic Reserve for property access, and funding through the OMNRF’s
Species at Risk Research Fund for Ontario (RF_47_17_WPC) and Species
at Risk Stewardship Fund (SARSF_84_17_WPC3), and W. Gareld Weston
Foundation.
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