A Wandering Monarch in a Milkweed Patch: some

ideas for butterfly conservation.Myron (‘Meron’) P. ZaluckiSchool of Integrative Biology

The University of Queensland, Australia

Acknowledgments

Lincoln Brower, Mike Bull, Tony Clarke, Hugh Dingle, Jane Hughes, Roger Kitching, Duncan Mackay, Steve Malcolm, Tim Paine, Wayne Rochester, Yoshito Suzuki, … and many others

Monarchs “down-under”

Applied entomology

Basic entomology

Will monarchs go extinct ?

Already an endangeredphenomenon! Will Bt corn, climate change, & herbicides impact on monarchs?

Climate & changes in abundance

Milkweed abundance at a landscape level & host plant search - metapopulations & habitat

Modelling risk…

What determines large scale fluctuations in monarch

abundance?

Climate...

• Affects milkweed• Affects reproduction & survival• Will have a strong influence on seasonal &

year to year abundance & distribution

+- D.plexippus

D.petilia

in North America

Year to year variation in climatic suitability

Expect large scale variation in abundance…

Milkweed

The distribution and abundance of host plant patches will have a dramatic effect on

monarch abundance

Metapopulation of interconnected milkweed patch ‘habitats’

Habitat?

Milkweed patch and surrounding ‘highish’ density of single plants defines breeding habitat.

Metapopulation of interconnected milkweed patch ‘habitats’

Space between is NOT empty!

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Age in Degree days (dz=11.5oC)

Monarch Reproduction

Zalucki. 1981. Res Pop Ecol 23: 318 - 27

Rules for egg layingIf (‘habitat’) lay all eggsIf (‘not habitat’) depends on isolated plants found

And that all depends on distribution and abundanceof milkweed and the monarchs ability to find these

What happens as the single plant density (SPD) increases in non-patch areas?

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Proportion of eggs laid as single plant density (SPD) increases in non-patch areasSearch parameter same for patches and singles

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Change in Proportion eggs laid

Search parameterH ---------------->L

Search parameterL ---------------->H

Prop Patch

H--->LSearch parameterH ---------------->L

Prop

Pat

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L--->

H

Returns on eggs will depend on factors affecting immature monarch survival

Zalucki, Clarke & MalcolmAnn Rev Ent 47: 361-393

Patches: 10%Singles: 20%

Predators?

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egg I II

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Early stage monarch survivalEarly stage survival & patch size: egg to II instar

Large larval survival:III to V instar

Patch plants 50%Single plants 33%

Food limitation?

Parasitism levels range from11-80 % in

winter/springto

38-99.9 % in summer/autumn

Patch plants 58%Single plants 36%

So putting eggs onsingle plants gives a higher return…

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Patch search

Random search for singles

Population persistencedepends very much onability to find plants bothas patches & singles

Proportion landscape withmilkweed patch habitat

Density of single plantsoutside milkweed patchhabitat

Population viability analysis of migratory monarch butterflies exposed to genetically

modified maize

Continental-scale resource use

Malcolm, Cockrell, & Brower, 1993

migration

Primary target of GM Bt-maize is the European corn borer

http://www.ent.iastate.edu/pest/cornborer/intro/intro.html

Non-target effects of Bt-maize pollen:

• Losey, Rayor & Carter, 1999. Nature 399: 214.– Larval mortality increased

44% in greenhouse.

• Hansen Jesse & Obrycki. 2000. Oecologia 125: 241-248.– 17-20% increase in

mortality of larvae exposed in the laboratory to Bt corn pollen deposited naturally on A. syriaca leaves.

Risk assessment• Sears et al. 2001 (PNAS 98) measured risk in Iowa as:

– R = Pe x Pt

• Risk = probability of exposure x probability of toxic effect– For Bt176 pollen:

• R = 0.0042 x 0.9 = 0.0038 (0.38%)– For Mon810 and Bt11 pollen:

• R = 0.0168 x 0.007 = 0.00012 (0.012%)– At 80% adoption this becomes:

• R = 0.067 x 0.007 = 0.00047 (0.047%)

• These estimates of R were revised by Dively et al. 2004 (Environ. Entomol. 33) to:– At 37% Bt corn use in Iowa, R = 0.0124 (1.24%)

• mortality of 2nd generation in Iowa.– At maximum 80% Bt corn use, R = 0.0261 (2.6%)

• Where Pe = proportion monarchs from maize (l) x overlap of pollen shed (o) x adoption rate of Bt maize (a).

What does this ‘low’ risk mean for monarch butterflies?

• We use the risk measures for monarch generation 2 of Dively et al. 2004 in a spatially discrete model of 4 linked generations where:– Gi = (Gi-1Ri + iGi-2Ri)SeSlSp

• G = generation size.• = proportion overlap

varies from 0 to 0.1.

• R = average realized fecundity.

• S = survivorship of eggs, larvae &

pupae.

G1

G2

G3

G4

time

lati

tud

e

overwinteringspring migration

autumnmigration

G3=Bt

Stochastic density independent models were run for 100 simulations

of 100 yearsMexico

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1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97

Year

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Mexico

Model 1 with random normally varying

reproduction and no Bt corn effect onsurvival in G3

with variable generation overlap[R = Pe x Pt = 0.0 x 0.07 = 0.0]

mean = 0/500 OW<500,000 (N=100)

Mexico

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Model 1 with random normally varyingreproduction and Bt corn effect on

survival in G3 and effect onreproduction in G4

with variable generation overlap[R = Pe x Pt = 0.024 x 0.07 = 0.002]mean = 0/500 OW<500,000 (N=100)

% extinction at overwintering threshold of

1 million monarchs vs exposure to Bt maize

Percentage of simulations in which N fell below theshold

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Pe (Proportion exposed to Bt) in DD Random 4

Pe

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10% carryover + 50% fecundity reduction

no carryover

Percentage of simulations in which N fell below threshold

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Pe (Proportion exposed to Bt) in DI Random 1

Perc

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no carryoverDensity independentmodel 1

Density dependentmodel 4

10% overlap + 50% fecundity reduction

no overlap

10% overlap + 50% fecundity reduction

no overlap

Will monarchs go extinct?• During the 2004/5 winter monarch overwintering

populations were the lowest recorded at 2.1 ha of overwintering forest in Mexico.– 10% of the largest recorded area of 21 ha in 1996/97.

Overwintering colony areas (hectares)(redrawn from Rendon and Galindo-Leal, 2005)

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Will monarchs go extinct?

• The conclusion of Sears et al. 2001 and Dively et al. 2004 that Bt maize poses low risk to monarchs is premature.

• Require more spatially and temporally relevant life-history data before reaching a conclusion.

Will monarchs go extinct?

• Need to determine the impact of added mortality from GM crops on the population dynamics of monarchs.

• A range of simulations suggests that the impact of Bt maize is not trivial.

• We also propose to address the impact of herbicide-tolerant soya beans.

Will monarchs go extinct ?

Don’t know … willdepend in part onclimate & hostplant distributionacross theLandscape & risks

For this wanderer in a milkweed patch