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Theresa Cira1, John Aigner2, Tom Kuhar2, Rob Venette3, Bill Hutchison1
1 University of Minnesota Department of Entomology2 Virginia Tech Department of Entomology
3 USDA Forest Service Northern Research Station
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• Basics of insect cold hardiness
• BMSB cold hardiness
• Future directions
• Question/comments
Outline
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• Short term (acute) cold
• Long term (chronic) cold• What stage overwinters?
• Where does it overwinter?
• Does it acclimate, diapause?
• What is its overwintering strategy?
• Low temperature limit?
Insect cold hardiness
How to study cold?
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• Short term (acute) cold hardiness
• Long term (chronic) cold hardiness• What stage overwinters?
• Where does it overwinter?
• Does it acclimate, diapause?
• What is its overwintering strategy?
• Low temperature limit?
Insect cold hardiness
How to study cold?
Adults
Aggregations, sheltered areas
? & no
?
BMSB stats:
?
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Insect cold hardiness
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Insect cold hardiness
Avoid the cold Survive freezingPrevent freezing
o Migrateo Aggregateo Seek shelter
o Supercoolo Void ice nucleatorso Accumulate
cryoprotectants(e.g. antifreeze proteins)
o Control the formation of ice in the body
Photo credits L to R: David R. Tribble, Pennsylvania Department of Conservation and Natural Resources, IronChris wikipedia.org Lee 2010, Salt 1961
Not mutually exclusive
Overwintering strategies
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MeasurementsSupercooling point (SCP) = lowest temp before exothermwhich indicates freezing
Mortality =
inability to walk or right itself
Insect cold hardiness
Denlinger & Lee 2010
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0
0.2
0.4
0.6
0.8
1
-23 -20 -17 -14 -11 -8 -5 -2 1 4 7 10 13 16 19 22 25
Pro
po
rtio
n
Cumulative SCP
Lee 2010, Salt 1961
Temperature °C
Insect cold hardiness
Hypothetical data
Frozen
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Lee 2010, Salt 1961
Temperature °C
Insect cold hardiness
Hypothetical data
0
0.2
0.4
0.6
0.8
1
-23 -20 -17 -14 -11 -8 -5 -2 1 4 7 10 13 16 19 22 25
Pro
po
rtio
n
Proportion mortality
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0
0.2
0.4
0.6
0.8
1
-23 -20 -17 -14 -11 -8 -5 -2 1 4 7 10 13 16 19 22 25
Pro
po
rtio
n
Cumulative SCP Proportion mortality
Lee 2010, Salt 1961
Temperature °C
Insect cold hardiness
Hypothetical data
Chill Intolerant
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0
0.2
0.4
0.6
0.8
1
-23 -20 -17 -14 -11 -8 -5 -2 1 4 7 10 13 16 19 22 25
Pro
po
rtio
n
Cumulative SCP Proportion mortality
Lee 2010, Salt 1961
Temperature °C
Insect cold hardiness
Hypothetical data
Freeze Intolerant
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0
0.2
0.4
0.6
0.8
1
-23 -20 -17 -14 -11 -8 -5 -2 1 4 7 10 13 16 19 22 25
Pro
po
rtio
n
Cumulative SCP Proportion mortality
Freeze Tolerant Lee 2010, Salt 1961
Temperature °C
Insect cold hardiness
Hypothetical data
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Do BMSB die before, as, or after they freeze?
Chill intolerant
Freeze intolerant
Freeze tolerant
Supercooling point
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Carillo 2004
Data logger
Syringe
Polystyrene cubeCooling at a rate of 1°C
Laptop
Copper constantan thermocouple wire
Methods
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-25 -15 -5 5 15 25
Pro
po
rtio
n
Temperature (°C)
Predicted mortality curve
Predicted SCP curve
Actual cumulative SCP
Actual mortality
SCP: n=19 bugs Mortality: n=17 bugs/each temp (mean ± 95% confidence interval)Regression curves fitted with a Weibull distribution
BMSB dies at significantly higher temperatures than they freeze (p = 0.04)Chill Intolerant
Results
Predicted and observed BMSB: Cumulative SCP & proportion mortality
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-25 -15 -5 5 15 25
Pro
po
rtio
n
Temperature (°C)
Predicted mortality curve
Predicted SCP curve
Actual cumulative SCP
Actual mortality
Results
-18°C
Lower Temperature at which there is 90% mortality (LT90)MN winter bugs LT90 = -18°C or ~0°F
Predicted and observed BMSB: Cumulative SCP & proportion mortality
SCP: n=19 bugs Mortality: n=17 bugs/each temp (mean ± 95% confidence interval)Regression curves fitted with a Weibull distribution
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= greater than -5 - 0°F
= less than -5 - 0°F
= -5 - 0°F zone
Results
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• Short term (acute) cold hardiness
• Long term (chronic) cold hardiness• What stage overwinters?
• Where does it overwinter?
• Does it acclimate, diapause?
• What is its overwintering strategy?
• Low temperature limit?
Results
Adults
Aggregations, sheltered areas
? & no
?
BMSB stats:
Chill Intolerant (dies before freezing)
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Do the following effect BMSB cold hardiness?
1) Season tested2) Acclimation location3) Sex
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Season: Spring = April and MaySummer = June, July, and AugustFall = September, October, NovemberWinter = December and February
Location: Blacksburg, VA Harper's Ferry, WV St. Paul, MN
Sex: Male Female
Methods
MN
VA
WV
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Results
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
SCP
(°C
)
Female
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
Male
WV
VA
MN
Mean supercooling points (±SEM)of BMSB
Assumptions tested with a Levene test and Shapiro-Wilk test and transformed according to Box-CoxANOVA performed at a 0.05 level and TukeyHSD used for mean separation of all main factors
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Results
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
SCP
(°C
)
Female
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
Male
WV
VA
MN
Mean supercooling points (±SEM)of BMSB
Assumptions tested with a Levene test and Shapiro-Wilk test and transformed according to Box-CoxANOVA performed at a 0.05 level and TukeyHSD used for mean separation of all main factors
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Results
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
SCP
(°C
)
Female
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
Male
WV
VA
MN
Mean supercooling points (±SEM)of BMSB
a aa b cc ba
Assumptions tested with a Levene test and Shapiro-Wilk test and transformed according to Box-CoxANOVA performed at a 0.05 level and TukeyHSD used for mean separation of all main factors
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Results
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
SCP
(°C
)
Female
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
Spring Summer Fall Winter
Male
WV
VA
MN
Mean supercooling points (±SEM)of BMSB
Assumptions tested with a Levene test and Shapiro-Wilk test and transformed according to Box-CoxANOVA performed at a 0.05 level and TukeyHSD used for mean separation of all main factors
a
c
b
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• Short term (acute) cold hardiness
• Long term (chronic) cold hardiness• What stage overwinters?
• Where does it overwinter?
• Does it acclimate, diapause?
• What is its overwintering strategy?
• Low temperature limit?
Results
Adults
Aggregations, sheltered areas
Yes & no
Varies by location, season, sex
BMSB stats:
Chill Intolerant (dies before freezing)
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That’s great, but BMSB numbers are only increasing
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• Short term (acute) cold hardiness
• Long term (chronic) cold hardiness• What stage overwinters?
• Where does it overwinter?
• Does it acclimate, diapause?
• What is its overwintering strategy?
• Low temperature limit?
Results
Adults
Aggregations, sheltered areas
Yes & no
Varies by location, season, sex
BMSB stats:
Chill Intolerant (dies before freezing)
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• Cold drives behavior– Study the triggers for overwintering behaviors– Study feeding at colder temperatures
• Cold can be directly lethal (but ecological relevance?)– Develop an estimate for what % of population is exposed to it
(remains outdoors in winter)– What shelters are sufficient buffers
• Sublethal effects of cold may be more important for BMSB– Investigate fitness effects of sublethal temperatures– Investigate effects of multiple stressors (e.g. insecticides, time)
• Indications of phenotypic variability in cold hardiness potential– Understand the overall variability in cold tolerance– Investigate mechanisms for variability (e.g. diet, genes)– Predictions need to account for geographic acclimation
Conclusions
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Acknowledgements
Virginia TechJohn Aigner, Dr. Tom Kuhar
USDA Forest ServiceDr. Rob Venette
University of MinnesotaDr. Bob Koch, Dr. Bill Hutchison, Eric Burkness, Amy
Morey, Jaana Iverson, Sarah Holle Erica Nystrom, Lindsey Christianson, Anthony Hanson, Andrea Hefty,
Kelly Nail, Derek Rosenburger, Amanda Stevens
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References
Questions?