Bumblebees:
Bumblebees:Cold
Coldtolerance
toleranceand
andimpacts
impactsof
ofdiet
diet
AAstudy
studyofofBuff-tailed
Buff-tailedBumblebees
Bumblebees(Bombus
(Bombusterrestris
terrestrisaudax)
audax)
Emily
Owen,
Jeff
Bale
and
Scott
Hayward
Emily
Owen,
Jeff
Bale
and
Scott
Hayward
School of Biosciences, University of Birmingham, B15 2TT Email: exo763@bham.ac.uk
School of Biosciences, University of Birmingham, B15 2TT Email: exo763@bham.ac.uk
COLD TOLERANCE
COLD TOLERANCE
Despite
thermal
biology
is largely
unknown
Despite
this,this,
theirtheir
thermal
biology
is largely
unknown
Bombus
terrestris
audax
Bombus
terrestris
audax
2 hour
2 hourtreatment
treatment
4 hour
4 hourtreatment
treatment
6 hour
6 hourtreatment
treatment
8 hour
8 hourtreatment
treatment
10 hour
treatment
10 hour
treatment
Predicted
from
Predicted
from SCP
-7.0
SCP profile
profile
-7.0
3
emergence
3
emergence (figure 1)
Colony
Colony
development
development
(production
(production
of workers)
of workers)
SUMMER
SUMMER
Colony death
Colony death
SPRING
SPRING
Colony
Colony
initiation
initiation
Queens
Queens
emerge from
emerge from
diapause
diapause
Males and
Males and
new queens
new queens
produced,
produced,
which mate
which mate
AUTUMN
AUTUMN
WINTER
WINTER
Males die,
Males die,
fertilised
fertilised
queens enter
queens enter
diapause
diapause
Research
aims
Research
aims
•
1.
2.
•
Why
is this
important?
Why
is this
important?
1.
2.
1. Optimising
commercial
usage
Optimising
commercial
usage
2. Conservation
Conservation
References
References
1. Rasmont et al. (2008) Annales de la Société Entomologique de France. 44(1):243-250
Rasmont
et al. (2008) Annales de la Société Entomologique de France. 44(1):243-250
2. Raine et al. (2006) Entomologia Generalis. 28(4):241-256
2. Raine
et al. (2006) Entomologia Generalis. 28(4):241-256
3. Dafini et al. (2010) Population Ecology. 46(3):243-251
3. Dafini et al. (2010) Population Ecology. 46(3):243-251
1.
Acknowledgements
Acknowledgements
Thanks to BBSRC for funding the project, Biobest for providing the bees and to Jeff Bale and Scott
Thanks
to BBSRC for funding the project, Biobest for providing the bees and to Jeff
Hayward for their continued support
Bale and Scott Hayward for their continued support
of cold tolerance in Bombus terrestris audax.
-6.5
-6.0
-6.0
-5.5
-5.0
-5.5
-5.0(°C)
Temperature
Temperature (°C)
100
100
90
90
80
80
70
70
60
60
50
50
40
40
30
30
20
20
10
10
0
-4.0 0
-4.5
-4.5
Results
Results
-4.0
Figure 2. Percentage survival of bumblebees (Bombus terrestris audax) after exposure to a range of sub-zero
temperatures
2h, 4h,
8h or 10h (±SE).
Survival
was assessed
72h after
each exposure,
for each value.
Figure 3.
Percentage for
survival
of6h,
bumblebees
(Bombus
terrestris
audax) after
exposure
to a rangen=30
of sub-zero
Figure 1. AFigure
summary
of the of
lifecycle
of Bombus
terrestrs
1. A summary
the lifecycle
of Bombus
terrestrsaudax
audax
1. Investigate
tolerance
of t.B.audax
t. audax
Investigate
thethe
coldcold
tolerance
of B.
2. Discover
if this
is affected
by diet
Discover
if this
is affected
by diet
Bees were
Beesfed
were
a standard
fed a standard
diet ofdiet
pollen
of pollen
and nectar.
and nectar.
Pollen
Pollen was
Type K exposed wire
was then
thenremoved
removedfor
for aa period of
of 0,0,3,3,7 or
7 or
14 days
14 days
respectively.
thermocouple
Figure 2.
respectively.
Individuals
Individuals
werewere
thenthen
transferred
transferred
to to
test
testtubes
tubesand each
Foam bung
and each
attached
attached
totoa athermocouple.
thermocouple.Test
Testtubes
tubeswere
werethen
then added to
added to
anan
alcohol
alcohol
bath,
bath,programmed
programmedtotocool
coolfrom
from20°C
20°Ctoto-20°C at a
Bombus terrestris
-1. The
-1. The
audax
-20°C atrate
a rate
of 0.2min
of 0.2min
supercooling
supercooling
pointpoint
(SCP)(SCP)
of each
of bee was
Figure 2. Apparatus used in the investigation
each bee
detected
was detected
by the by
exotherm
the exotherm
on freezing.
on freezing.
Results
Results
-6.5
•
•
Method
Method
Test tube
Bees Bees
werewere
takentaken
fromfrom
theirtheir
rearing
temperature
(20⁰C)
andand
rearing
temperature
(20⁰C)
transferred
to test
tubestubes
which
werewere
thenthen
plunged
intointo
a pretransferred
to test
which
plunged
a preprogrammed
alcohol
bath bath
set atseta at
range
of temperatures
(30 (30
bees
programmed
alcohol
a range
of temperatures
bees
per treatment,
figure 2).Survival
Survivalwas
was assessed
exposure.
per treatment).
assessed 72h
72hafter
after
exposure.
Preliminary
experiments
involvedinvolved
measuring
the supercooling
points
Preliminary
experiments
measuring
the supercooling
of 30points
bees and
using
data
to construct
a profile
of the
expected
of 30
beesthis
and
using
this data to
construct
a profile
of the
freezing
temperatures
the bumblebee
population.
expected
freezingof
temperatures
of the
bumblebee population.
1
•
UK
native
subspecies,
8
European
conspecifics
1
• UK native subspecies, 8 European conspecifics
2
•
Diet
of
pollen
and
nectar
2
• Diet of pollen and nectar
• Can
generate
their
own
heat
→ early
spring
• Can
generate
their
own
heat
→ early
spring
DIETDIET
ANDAND
SUPERCOOLING
POINT
SUPERCOOLING
POINT
Survival (%)
Bumblebees
economically
important
Bumblebees
are are
economically
important
cropcrop
pollinators
extensive
commercial
usage
pollinators
withwith
extensive
commercial
usage
MethodMethod
Survival (%)
INTRODUCTION
INTRODUCTION
To computer
Figure 3. Supercooling points of bumblebees (Bombus terrestris audax) that were
temperatures for 2h, 4h, 6h, 8h or 10h (±SE). Survival was assessed 72h after each exposure, n=30 for each value.
Figure 4. Supercooling points of bumblebees (Bombus terrestris audax) that were fed
fed either pollen and nectar or nectar alone for 3, 7 or 14 days respectively, n=30
either pollen and nectar or nectar alone for 3, 7 or 14 days respectively (±SE), n=30 for
for each treatment. Corresponding letters indicate significance ≤0.01.
each treatment. Corresponding letters indicate significance ≤0.01.
Discussion
Discussion
Discussion
Discussion
• Bumblebees
to tolerate
temperatures
as -5low
as 10h
-5°Cwithout
for 10hsignificant
without
Bumblebees
were were
able toable
tolerate
temperatures
as low as
°C for
significant
mortality
(figuremortality
3)
• Below
survival
deviated
predicted
values
if freezing
sole
cause
Below
-5°C, -5°C,
survival
deviated
fromfrom
the the
predicted
values
if freezing
waswas
thethe
sole
cause
of
death;
withdurations
longer durations
lowerThis
survival.
Thiscanmortality
can be
death;ofwith
longer
producing producing
lower survival.
mortality
be attributed
to
attributed to cold shock
cold shock
• In other
insects,
is usually
a temperature
window
between
cold
In other
insects,
therethere
is usually
a temperature
window
between
deathdeath
due todue
coldtoshock
shockdue
andto
death
due to
In B.
t. audax,
window is comparatively
small
and death
freezing.
In freezing.
B. t. audax,
this
windowthis
is comparatively
small
• Potentially,
this means
bumblebees
can survive
at temperatures
their
Potentially,
this means
bumblebees
can survive
at temperatures
close toclose
their to
freezing
freezing temperature
temperature
• When fed the standard diet of pollen and nectar, the SCP ranged
• When fed the standard diet of pollen and nectar, the SCP ranged from
from -5°C to -10.9°C (mean -7.1 ± 0.22°C)
-5°C to -10.9°C (mean -7.1 ± 0.22°C, figure 4)
• After removal of pollen from the diet, the SCP decreased to a
• After removal of pollen from the diet, the SCP decreased to a
minimum of -17.9°C (mean of 14 day nectar-feeding -12.5 ±
minimum of -17.9°C after 14 days of nectar-feeding (mean -12.5 ±
0.52°C)
0.52°C)
• Pollen is a known ice nucleator and causes freezing at higher
• Pollen is a known ice nucleator and causes freezing at higher
temperatures. These data suggest that pollen appears to
temperatures.
contribute to the increase in SCP for pollen-feeding bumblebees
• These data suggest that pollen appears to contribute to the increase
in SCP for pollen-feeding bumblebees
CONCLUSIONS
CONCLUSIONS
1. 1.Bumblebees
tolerate
temperatures
down
to -5°C
without
a significant
decrease
in survivorship.
Below
thisthis
temperature,
death
was
Bumblebees
tolerate
temperatures
down
to -5°C
without
a significant
decrease
in survivorship.
Below
temperature,
death
caused
a combination
of freezing
and coldand
shock
was by
caused
by a combination
of freezing
cold shock
2. 2.Pollen
in the
dietdiet
increased
bumblebees’
freezing
temperature,
making
them
susceptible
to freezing
at higher
temperatures
Pollen
in the
increased
bumblebees’
freezing
temperature,
making
them
susceptible
to freezing
at higher
temperatures