-6.8 -6.3 -5.8 -5.3 -4.8 -4.3 -3.80
10
20
30
40
50
60
70
80
90
1002 hour treatment
4 hour treatment
6 hour treatment
8 hour treatment
10 hour treatment
Predicted
Temperature (°C)
Su
rviv
al (%
)
from SCP profile
INTRODUCTION
Bumblebees are economically important crop pollinators with extensive commercial usage
Despite this, their thermal biology is largely unknown
Bumblebees: Cold tolerance and impacts of dietA study of Buff-tailed Bumblebees (Bombus terrestris audax)
Emily Owen, Jeff Bale and Scott HaywardSchool of Biosciences, University of Birmingham, B15 2TT Email: [email protected]
Colony death
Colony development (production of workers)
Queens emerge from diapause
Males and new queens produced, which mate
Males die, fertilised queens enter diapause
SUMMER
AUTUMN
WINTER
SPRING
Results
DiscussionResearch aims1. Investigate the cold tolerance of B. t. audax2. Discover if this is affected by diet
Why is this important?3. Optimising commercial usage4. Conservation
• Bumblebees were able to tolerate temperatures as low as -5°C for 10h without significant mortality
• Below -5°C, survival deviated from the predicted values if freezing was the sole cause of death; with longer durations producing lower survival. This mortality can be attributed to cold shock
• In other insects, there is usually a temperature window between death due to cold shock and death due to freezing. In B. t. audax, this window is comparatively small
• Potentially, this means bumblebees can survive at temperatures close to their freezing temperature
Bombus terrestris audax
• UK native subspecies, 8 European conspecifics1
• Diet of pollen and nectar2
• Can generate their own heat → early spring
emergence3
• When fed the standard diet of pollen and nectar, the SCP ranged from -5°C to -10.9°C (mean -7.1 ± 0.22°C)
• 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 ± 0.52°C)
• Pollen is a known ice nucleator and causes freezing at higher temperatures. These data suggest that pollen appears to contribute to the increase in SCP for pollen-feeding bumblebees
CONCLUSIONS1. Bumblebees tolerate temperatures down to -5°C without a significant decrease in survivorship. Below this temperature, death
was caused by a combination of freezing and cold shock2. Pollen in the diet increased bumblebees’ freezing temperature, making them susceptible to freezing at higher temperatures
Results
Discussion
Figure 2. Percentage survival of bumblebees (Bombus terrestris audax) after exposure to a range of sub-zero temperatures for 2h, 4h, 6h, 8h or 10h (±SE). Survival was assessed 72h after each exposure, n=30 for each value.
Figure 3. Supercooling points of bumblebees (Bombus terrestris audax) that were fed either pollen and nectar or nectar alone for 3, 7 or 14 days respectively, n=30 for each treatment. Corresponding letters indicate significance ≤0.01.
Colony initiation
References1. Rasmont et al. (2008) Annales de la Société Entomologique de France. 44(1):243-2502. Raine et al. (2006) Entomologia Generalis. 28(4):241-2563. Dafini et al. (2010) Population Ecology. 46(3):243-251
AcknowledgementsThanks to BBSRC for funding the project, Biobest for providing the bees and to Jeff Bale and Scott Hayward for their continued support
Figure 1. A summary of the lifecycle of Bombus terrestrs audax
DIET AND SUPERCOOLING POINT
Bees were taken from their rearing temperature (20⁰C) and transferred to test tubes which were then plunged into a pre-programmed alcohol bath set at a range of temperatures (30 bees per treatment). Survival was assessed 72h after exposure. Preliminary experiments involved measuring the supercooling points of 30 bees and using this data to construct a profile of the expected freezing temperatures of the bumblebee population.
MethodCOLD TOLERANCE
Bees were fed a standard diet of pollen and nectar. Pollen was then removed for a period of 0, 3, 7 or 14 days respectively. Individuals were then transferred to test tubes and each attached to a thermocouple. Test tubes were then added to an alcohol bath, programmed to cool from 20°C to -20°C at a rate of 0.2min-1. The supercooling point (SCP) of each bee was detected by the exotherm on freezing.
Method
Figure 2.
-6.8 -6.3 -5.8 -5.3 -4.8 -4.3 -3.80
10
20
30
40
50
60
70
80
90
1002 hour treatment
4 hour treatment
6 hour treatment
8 hour treatment
10 hour treatment
Predicted
Temperature (°C)
Su
rviv
al (%
)
from SCP profile
INTRODUCTION
Bumblebees are economically important crop pollinators with extensive commercial usage
Despite this, their thermal biology is largely unknown
Bumblebees: Cold tolerance and impacts of dietA study of Buff-tailed Bumblebees (Bombus terrestris audax)
Emily Owen, Jeff Bale and Scott HaywardSchool of Biosciences, University of Birmingham, B15 2TT Email: [email protected]
Results
DiscussionResearch aims1. Investigate the cold tolerance of B. t. audax2. Discover if this is affected by diet
Why is this important?3. Optimising commercial usage4. Conservation
• Bumblebees were able to tolerate temperatures as low as -5°C for 10h without significant mortality (figure 3)
• Below -5°C, survival deviated from the predicted values if freezing was the sole cause of death; with longer durations producing lower survival. This mortality can be attributed to cold shock
• In other insects, there is usually a temperature window between death due to cold shock and death due to freezing. In B. t. audax, this window is comparatively small
• Potentially, this means bumblebees can survive at temperatures close to their freezing temperature
Bombus terrestris audax
• UK native subspecies, 8 European conspecifics1
• Diet of pollen and nectar2
• Can generate their own heat → early spring
emergence3
(figure 1)
• When fed the standard diet of pollen and nectar, the SCP ranged from -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 minimum of -17.9°C after 14 days of nectar-feeding (mean -12.5 ± 0.52°C)
• Pollen is a known ice nucleator and causes freezing at higher temperatures.
• These data suggest that pollen appears to contribute to the increase in SCP for pollen-feeding bumblebees
CONCLUSIONS1. Bumblebees tolerate temperatures down to -5°C without a significant decrease in survivorship. Below this temperature, death was
caused by a combination of freezing and cold shock2. Pollen in the diet increased bumblebees’ freezing temperature, making them susceptible to freezing at higher temperatures
Results
Discussion
Figure 3. Percentage survival of bumblebees (Bombus terrestris audax) after exposure to a range of sub-zero 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 either pollen and nectar or nectar alone for 3, 7 or 14 days respectively (±SE), n=30 for each treatment. Corresponding letters indicate significance ≤0.01.
Colony death
Colony development (production of workers)
Queens emerge from diapause
Males and new queens produced, which mate
Males die, fertilised queens enter diapause
SUMMER
AUTUMN
WINTER
SPRINGColony initiation
References1. Rasmont et al. (2008) Annales de la Société Entomologique de France. 44(1):243-2502. Raine et al. (2006) Entomologia Generalis. 28(4):241-2563. Dafini et al. (2010) Population Ecology. 46(3):243-251
AcknowledgementsThanks to BBSRC for funding the project, Biobest for providing the bees and to Jeff Bale and Scott Hayward for their continued support
Figure 1. A summary of the lifecycle of Bombus terrestrs audax
Bees were taken from their rearing temperature (20⁰C) and transferred to test tubes which were then plunged into a pre-programmed alcohol bath set at a range of temperatures (30 bees per treatment, figure 2). Survival was assessed 72h after exposure. Preliminary experiments involved measuring the supercooling points of 30 bees and using this data to construct a profile of the expected freezing temperatures of the bumblebee population.
MethodCOLD TOLERANCE
MethodDIET AND SUPERCOOLING POINT
Bees were fed a standard diet of pollen and nectar. Pollen was then removed for a period of 0, 3, 7 or 14 days respectively. Individuals were then transferred to test tubes and each attached to a thermocouple. Test tubes were then added to an alcohol bath, programmed to cool from 20°C to -20°C at a rate of 0.2min-1. The supercooling point (SCP) of each bee was detected by the exotherm on freezing.
To computer
Test tube
Type K exposed wire thermocouple
Foam bung
Bombus terrestris audax
Figure 2. Apparatus used in the investigation of cold tolerance in Bombus terrestris audax.
