Epidemiology M.S. thesis defense presentation final

Effects of temperature regimes and population source on the success, timing, and host plant synchrony of egg hatch by Forest Tent Caterpillar (Malacosoma disstria Hübner)

Johnny A. Uelmen Jr.University of Wisconsin-MadisonDepartment of EntomologyM.S. Thesis Defense Presentation

Advisors:Ken Raffa, Rick Lindroth, Eric Kruger, Ezra Schwartzberg

Outline

• Section 1: Climate warming and plant-insect phenology

• Section 2: Supercooling points and diapausing forest tent caterpillar egg bands

• Section 3: Integration and “big picture”

Chapter 1: Climate Warming and Plant-Insect Phenology

Boreal Forest of North America

• Ecotones, like the Southern Boreal Forest, are experiencing drastic climate warming forces

• Mean annual temperature has risen ~1.5° C since 1940; Additional 3-5° C (winter), 4-9° C (summer) expected by 2095 (Kling et al. 2003)

• One consequence needing investigation: Tree phenology

and synchrony of early-season Insect folivores

3 Hypotheses

Host plant

Insect herbivore

Dev

elop

men

t(E

gg H

atch

, Bud

Bre

ak)

Time (days)

Both advance equally

Plant advances more than insect

Insect advances more than plant

Time

Future?

How Will Warming Temperatures AffectPhenological Synchrony Between Early-Season Folivores and Host Plant?

Ecological Context: Given that insects can migrate (in a relatively short time) and trees cannot, what will the relative change in phenology be between host trees and insects folivores under increasing temperatures?

Research QuestionsMain Question: How will warming temperatures affect phenological synchrony between early-season folivores and host plants?

Specific Questions:1. Under increased temperatures, how does larval eclosion differ among

spring folivore populations along a latitudinal gradient?2. What role does the overwintering location (and extreme cold

temperatures) have on each insect population’s hatch?

• Forest Tent Caterpillar (FTC) M. disstria – Occurs throughout U.S. and Canada– Strong fliers

• Host trees: prefer *aspen, *birch, oaks, basswood • Egg masses contain 100-350 eggs• Larvae emerge mid April – early May • Often cause severe defoliation

Selection of Test Model

* Denotes host plants used in study

Insect Folivores And Their Host Plants:A Meso-Scale Climate Change Simulation

• Outdoor temperature rings simulate climate change– Provides uniform heat both above and belowground • 3 temperature regimes: ambient, +1.7 °C and +3.4 °C

• Evaluation of natural disturbances from climate change through direct measures

Experimental Unit

Experimental Design

288 egg bands total

• Experimental Unit = Temperature Ring • composed of a temperature-population source-overwintering treatment combinations

• 6 replicates per temperature treatment

8 M. disstria egg bands per ring (4 per population x 2 per overwintering location*)

6 rings per temperature treatment

3 temperature treatments per site2 sites total

*3 total overwintering locations (2 per ring)

144

72

72December to Mid-March

Stage 1 Overwintering Phase

72

72

72Mid-March

72

Stage 2 Overwintering Phase: Egg Transfer

Ely and Cloquet each have a total of 144 egg masses at this point

Statistical AnalysesInsect and Host Plant PhenologyTwo part analysis:• Discrete Analyses (ANOVA)– Tested main effects with categorical temperature factor– Characterize and quantify all sources of variation

• Nested Design• Continuous Analysis (ANCOVA, ANOVA)– Integrate and expand the generality of results across a common

continuous temperature• Accumulated Degree Days (FTC specific)– Integration of time component with biological threshold

• Mean Ring Temperature (for analysis of host plants, and host plants compared with insects)

Egg hatch Mortality

• Analysis of Variance• Not significant for any treatment - Ely (hatch site) moderately significant

(p = 0.055)• High proportion of successful egg

hatch for all populations (> 81%)

Source DF F PModel 47 0.82 0.784Error 235

Site 1 3.74 0.055Pop. 3 1.55 0.204Site*Pop. 3 0.27 0.849Overwinter 2 0.23 0.791Overwinter*Pop. 6 0.83 0.55Temp. (°C) 2 0.06 0.943Temp. (°C)*Site 2 0.84 0.432Temp. (°C)*Pop. 6 0.42 0.869Temp. (°C)*Site*Pop. 6 0.97 0.45Temp. (°C)*Overwinter 4 0.17 0.954Temp. (°C)*Overwinter*Pop. 12 1.25 0.251

Overwintering Treatment

Proportion of Successful Egg Hatch

df F PInsect Population

Bemidji Mille Lacs Lake Baraboo Prairie du Chien

Ely 0.825 0.826 0.795 0.722 3 1.28 0.288Cloquet 0.828 0.843 0.78 0.817 3 0.73 0.538Madison 0.828 0.798 0.785 0.807 3 0.42 0.738df 2 2 2 2 5 -- --F 0 0.7 0.03 1.28 -- 0.82 --P 0.995 0.5 0.967 0.284 -- -- 0.537

M. disstria egg hatch date

Discrete Analysis (ANOVA): - Overwintering Location, Temperature Treatment, Population Source and Hatch Site are all significant

- All Populations Respond Similarly To Warming Temperatures

- In addition to warming temperature, southerly overwintering and hatch site locations experience earliest egg hatch

Source DF F PDay of Hatch Model 27 11.18 <0.0001* Error 256

Site 1 33.18 <0.0001* Temp. (°C) 2 61.13 <0.0001* Overwinter 2 19.32 <0.0001* Pop. 3 19.02 <0.0001* Temp. (°C)*Pop. 6 0.34 0.822

Temp. (°C)*Overwinter 4 0.98 0.849

Overwinter*Pop. 6 1.37 0.228


Main Effect: Site -Cloquet egg bands hatched 3 days earlier than Ely










Main Effect: Temperature Treatment (°C) -Temperature treatment varied by 6.5 days between warmest (+3.4°C) treatment and control (ambient)-Temperature treatment varied by 4 days between intermediate (+1.7°C) treatment and control-Temperature treatment varied by 2.5 days between warmest (+3.4°C) treatment and intermediate (+1.7°C) treatment






Main Effect: Overwintering Location-Madison overwintered egg bands hatched 3 days earlier than locally overwintered egg bands






Main Effect: Population Source-Baraboo egg bands hatched the earliest-Lake Mille Lac egg bands hatched 2 days after Baraboo-The northernmost population, Bemidji, hatched 4 days after Baraboo-The southernmost population, Prairie du Chien, hatched the latest (6 days after Baraboo)

*Egg hatch by population does not follow a strict latitudinal gradient


Discrete Analysis (ANOVA): - Overwintering Location, Temperature Treatment, Population Source and Hatch Site are all significant

- All Populations Respond Similarly To Warming Temperatures

- In addition to warming temperature, southerly overwintering and hatch site locations experience earliest egg hatch





M. disstria egg hatch dateContinuous Analysis (ANCOVA): - Madison and Locally overwintered insects hatch rate the same- Madison overwintered insects hatch begins and ends earlier than Locally overwintered insects

Source Overwintering a b r2 DF F PProportion Cumulative Hatch Model Locally 0.0049 -0.659 0.426 4 26.05 <0.0001* Error 136

Accumulated Degree-days 1 82.4 <0.0001* Pop. 3 0.6 0.617 Model Madison 0.0051 -0.604 0.533 4 43.73 <0.0001* Error 138

Accumulated Degree-days 1 104.74 <0.0001* Pop. 3 2.75 0.045*

M. disstria duration of hatch

Discrete Analysis (ANOVA): - Temperature Treatment was not a factor

with insect egg hatch- The earliest overwintering/hatch site

combination (Madison/Cloquet) showed the longest hatch duration

- Is it possible insect larvae can “wait”?

Source DF F PHatch Duration Model 27 3.62 <0.0001* Error 256

Site 1 29.43 <0.0001* Temp. (°C) 2 2.15 0.119 Overwinter 2 11.57 <0.0001* Pop. 3 3.92 0.0092* Temp. (°C)*Pop. 6 0.79 0.575


Overwinter*Pop. 6 1.03 0.409 Site*Pop. 3 1.33 0.264


Main Effect: Site -Ely hatch duration was 2.5 days less than Cloquet










Main Effect: Overwintering Location -Locally overwintered egg hatch duration was 2.5 days less than Cloquet






Main Effect: Population Source-The southernmost population, Prairie du Chien (PDC), displayed the shortest hatch duration-The northernmost population, Bemidji, hatch duration 0.25 days longer than PDC-Lake Mille Lac hatch duration 1 day longer than PDC-Baraboo’s hatch duration was the longest (1.5 days longer than PDC)

*Similarly to hatch date, hatch duration by population does not follow a strict latitudinal gradient


Discrete Analysis (ANOVA): - Temperature Treatment was not a factor

with insect egg hatch- The earliest overwintering/hatch site

combination (Madison/Cloquet) showed the longest hatch duration

- Is it possible insect larvae can “wait”?





M. disstria duration of hatchContinuous Analysis (ANOVA): - Earliest hatching egg bands displayed the greatest duration of hatch- Variation indicated by 95% confidence intervals

F1, 282 = 132.17, P < 0.0001, N = 284

a = -1.526, b = 24.787, r2 = 0.319

F1, 282 = 98.2, P < 0.0001, N = 284

a = -9.906, b = 281.36, r2 = 0.258

Host Plant Budbreak DateDiscrete Analysis (ANOVA): - Aspen and Birch both respond similarly to warming temperatures

- Birch responds earlier- Site was marginally significant for Birch (p > 0.087)

Source DF F PAspen Budbreak Model 5 26.58 <0.0001* Error 62

Temperature Treatment (°C) 2 56.22 <0.0001* Site 1 19.97 <0.0001* Temperature Treatment (°C)*Site 2 0.28 0.7597Birch Budbreak Model 5 10.16 <0.0001* Error 63

Temperature Treatment (°C) 2 23.27 <0.0001* Site 1 3.02 0.087 Temperature Treatment (°C)*Site 2 0.35 0.707

M. disstria and host plant phenology

Discrete Analysis (ANOVA): - Birch clearly ahead of insects throughout experiment- Aspen well in “range” of insect hatch

Source DF F PEgg hatch to aspen budbreak Model 5 24.23 <0.0001*

Error 278

Temperature Treatment (°C) 2 54.39 <0.0001* Site 1 10.78 0.0012* Temperature Treatment (°C)*Site 2 1.21 0.300Egg hatch to birch budbreak Model 5 16.26 <0.0001* Error 278

Temperature Treatment (°C) 2 10.85 <0.0001* Site 1 56.87 <0.0001* Temperature Treatment (°C)*Site 2 0.91 0.406

Birch & FTC

Aspen & FTC

Continuous Analysis (ANCOVA):- Insects initially before Aspen and Birch- Birch and Aspen advancement more rapid with increasing temperature; Aspen “catching up”

to Birch

M. disstria and host plant phenology

Source a b r2 DF F PAspen Budbreak Model 0.141 -12.816 0.688 7 1.49 <0.0001* Error 65

Accumulated Degree-days 1 96.54 <0.0001* Site 1 0.79 0.378Birch Budbreak Model 0.15 -15.75 0.667 2 65.85 <0.0001* Error 66

Accumulated Degree-days 1 127.5 <0.0001* Site 1 0.02 0.892

Source a b r2 DF F PAspen Budbreak Model -3.614 52.511 0.382 2 35.44 <0.0001* Error 65

Mean Ring Temp. (°C) 1 59 <0.0001* Site 1 14.72 0.0003*Birch Budbreak Model -2.664 34.924 0.267 2 14.56 <0.0001* Error 66

Mean Ring Temp. (°C) 1 27.09 <0.0001* Site 1 1.38 0.244

Continuous Analysis (ANCOVA):- Both species’ budbreak dates are ahead of insect egg hatch with warming temperatures (and increasing in disparity)- Lines remain parallel, displaying similar relationship of Aspen and Birch budbreak phenology differences with M. disstria.

Days between Egg hatch and Budbreak

*Phenology was also significant for mean ring temperature

Source a b r2 DF F PEgg hatch to aspen budbreak Model -0.374 8.439 0.05 4 2.64 0.036* Error 138

Accumulated Degree-days 1 8.23 0.0048* Population 3 0.3 0.826Egg hatch to birch budbreak Model -0.045 2.742 0.067 4 5.2 0.0006* Error 138

Accumulated Degree-days 1 18.61 <0.0001* Population 3 0.63 0.598

Population a b r2 DF F P

Egg hatch to aspen budbreak

Bemidji Model -0.06923 0.02188 0.1252 1 10.01 0.0023* Error 70Mille Lacs Lake Model -0.01532 2.05523 0.0075 1 0.51 0.476 Error 68Baraboo Model -0.00339 0.56161 0.0004 1 0.03 0.871 Error 69Prairie du Chien Model -0.02701 4.44557 0.034 1 2.43 0.124 Error 69

Egg hatch to birch budbreak

Bemidji Model -0.08185 10.05625 0.1691 1 14.25 0.0003* Error 70Mille Lacs Lake Model -0.0343 -1.47063 0.0334 1 2.35 0.13 Error 68Baraboo Model -0.01201 -5.11005 0.0042 1 0.29 0.593 Error 69Prairie du Chien Model -0.04752 2.30867 0.0836 1 6.29 0.015* Error 69

Continuous Analysis (ANCOVA):- Both species’ budbreak dates are ahead of insect egg hatch with warming temperatures (and increasing in disparity)- Lines are converging as temperatures warm, showing trend of Aspen budbreak’s late, but rapid response to increasing temperatures

Days between Egg hatch and Budbreak

Outline




Chapter 2: Supercooling point determination of M. disstria eggs

• Malacosoma disstria’s range is vast, extending from Nova Scotia to Florida, to British Columbia and California.

• Many populations subjected to extended period of subzero temperatures

• Ability to disperse up to 19 km a year

• Other than intermittent snow, ice, and spumulin coating, eggs have minimal protection from harsh winter conditions.

http://mothphotographersgroup.msstate.edu/large_map.php?hodges=7698

2013 Forest Tent Caterpillar Distribution

Ecological Context: Climate change is likely to facilitate northward expansion of many insect species in north-temperate zones, but how will winter temperatures affect migrating populations across a latitudinal gradient?

Additional Question:How does egg survival among southern insect populations compare to that of northern insect populations?

Research QuestionsMain Question: How does extreme winter temperatures affect survival and cold tolerances among M. disstria eggs?

Range expansion in north-temperate zones

??

?

Test Specifics

• Supercooling point (SCP) tests performed at Univ. Notre Dame

• Micro-thermocouples applied to individual 1421 eggs• SCP determined as temperature immediately before

exotherm, or burst of energy released upon threshold applied by incremental cooling– Cooled at a rate of 0.2°C/min

Individual egg masses tested

http://www.entomology.umn.edu/cues/extpubs/7563ftc/7563f02a.gif

Experimental Design (N = 1421 egg bands)

SCP tests performed on:1. Effects of winter time period• *Early Nov. 2011 (n = 56), early Feb. 2012 (n = 440), and

early Mar. 2012 (n = 925)2. Effect on 4 population sources• Bemidji (n = 394), Mille Lacs Lake (n = 357), Baraboo (n =

355), and Prairie du Chien (n = 259)3. Effects on 3 overwintering regimes• Ely, MN (n = 436), Cloquet, MN (n = 489), and Madison, WI

(n = 440)

*Pooled population sources (n = 56) only included in first test

Statistical AnalysisSupercooling point determination:• Three separate analyses of variance– 1. Effects of winter period (n=3)

• November, February, and March testing periods– 2. Differences in population source (n=4)

• February time period only– 3. Effects of population source and overwintering location,

and their interaction• March time period only

Supercooling Point (SCP) Results3 independent ANOVAs• The effects of time period (A),

population source (Feb. only) (B), and population source*overwintering location (Mar. only) (C) all display variation on supercooling points of M. disstria egg bands.

A

B

C

Source DF F P

Effect of Time Period

Model 2 408.33 <0.0001*Error 1417

Date 2 408.33 <0.0001*

Source DF F P

Effect of Population Source

Model 3 20.07 <0.0001*Error 436

Pop 3 20.07 <0.0001*

Source DF F P

Effect of Population Source and Overwintering Location

Model 7 27.77 <0.0001*Error 916

Pop 3 48.26 <0.0001*Overwintering Location 1 4.09 0.043*

Pop*Overwintering Location 3 15.72 <0.0001*

Supercooling Point (SCP) SummaryDate Overwintering Location Population

Supercooling Point (°C)

Mean SE N1-November-2011 At Population Sourcea Pooled -26.8 0.5 56

1 February 2012 Madison

Bemidji -38.3 0.4 129Mille Lacs Lake -36.8 0.2 128

Baraboo -40.3 0.3 85Prairie du Chien -38.4 0.3 98

Pooled -38.3 0.2 440

9 March 2012

Ely

Bemidji -39 0.2 117Mille Lacs Lake -37.4 0.2 113


Pooled -37.6 0.1 436

Cloquet



Pooled -37.5 0.1 489

Pooled



Pooled Pooled -37.6 0.1 925

aEggs tested in November did not undergo an overwintering treatment, as they were tested immediately after field collection.

Outline




3 Hypotheses

Host plant

Insect herbivore

Dev

elop

men

t(E

gg H

atch

, Bud

Bre

ak)

Time (days)

Both advance equally

Plant advances more than insect

Insect advances more than plant

Time

Future?

Putting it all together…

Plant advances more than insect!

Putting it all together…

Population km South of Sitesa

Number of Added Degree-Days that will Reconstruct Local ConditionsTo Become Synchronous with Aspen To Become Synchronous with BirchBased on Median Based on Mean Based on Median Based on Mean

Bemidji 0 24.08 23.56 52.74 58.21Mille Lacs Lake 140.33 27.93 18.13 56.59 52.78

Baraboo 451.82 11.4 -0.29 40.06 34.36Prairie du Chien 496.57 45.84 36.04 74.5 70.69

aMidpoint between Ely and Cloquet, MN.

✓FTC northern migration seems highly likely because:• Climate change is increasing annual temperatures, and

leading to earlier insect egg hatch• Host plant nutrient availability is less certain, but…

• Many “migrating” insects were able to be synchronous

• Late-hatching insects are still capable of reaching pupation with less nutritious foliage

• High overwintering survival• Strong fliers and dispersal rates per generation• Based on this study, very few degree-days are required

for mean egg band synchrony with northernmost “local” population

✓✓

Conclusions• FTC Egg Hatch varies by population source,

overwintering regime, hatch site, and temperature treatment– Insect mortality only marginally significant for hatch site (Ely)

• Insect Hatch and Plant Phenology occur earlier with increasing temperatures– Plant Phenology occurs ahead of Insect Egg Hatch– Birch Budbreak occurs earlier than Aspen Budbreak

• Disparity Between Egg hatch to Plant Budbreak Increase with increasing temperature– Aspen has rapid response to warmer temperatures

• All populations are very cold tolerant– Protected from extreme cold temperatures

So Who “Wins”?!• Can make a case for both insect and host plant

– Initial results seem to show Birch and Aspen “pulling away”– However, even “late” hatching larvae still seem to feed and reach

pupation (albeit later) on developed foliage– At what temperature does each system reach it’s “maximum”?

• Future studies needed to provide more evidence include:– Chemical analysis of foliage and insect success– Additional insect population sources (with extended latitudinal range)– Higher sample size and replicates for SCP study– Open to more species of insects (gypsy moth, spruce budworm) and

host plants with similar phenologies (oak, birch, ash, cherry)

Acknowledgments

Funding Sources: USDA AFRI, University of Wisconsin

Patrick Tobin - USFS Jun Zhu - UW-Madison Mary Jamieson UW-Madison

Rick LindrothUW-Madison

Peter ReichUniv. of Minnesota

Ken RaffaUW-Madison

Jana AlbersMN DNR

Ezra SchwartzbergUW-Madison

Experimental Design

1 egg band 2 wintering sites 6 rings 3 temperature treatments

wintering site ring temperature treatment 1 site population

72 egg bands 4 populations

288 egg bands total

2 sites

• Experimental Unit = Temperature Ring • composed of a temperature-population source-overwintering treatment combinations

• 6 replicates per temperature treatment

population

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Cloquet Ely

Environment

Epidemiology M.S. thesis defense presentation final