Ecological Effects of Leaf MiningPlant Performance and Trophic Dynamics

Diane Wagner

LTER SymposiumFebruary 2014

2

Acknowledgements

• Collaborators– Pat Doak– Knut Kielland– Tom Clausen– Linda Defoliart– Jenny Schneiderheinze

• Graduate students – Brian Allman– Brent Mortensen– Jonathon Newman– Adam Watson– Brian Young

Local leaf miner and chewers densities on deciduous trees

BC LTER: Defoliating Insect Population Levels – Werner & Kruse

Year

Num

ber insects m-2

0

50

100

150

200

250

Leaf minersExternal chewers

Major leaf miner outbreaks across Alaska

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

2012

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000 Aspen leaf miner Willow leaf blotch miner

Area

infe

sted

(ha)

Aerial Insect Detection Survey – USFS

Outline

• Why did ALM outbreak last so long?• What caused the end of the ALM outbreak? • How does aspen leaf miner (ALM) affect aspen

performance?• New experiment: Long term ecosystem

consequences of insect herbivory, mammalian browsing, and their interaction

7

Aspen leaf miner moth (Phyllocnistis populiella)

North American native One generation per year Larvae consume epidermal

cell layer Restricted to one side of a

single leaf until adulthood Adults emerge in June,

overwinter under spruce

Why did the ALM outbreak last so long?

• High plant tolerance of herbivory– Nutrient stores

• Insect behavior– Larvae unable to attack foliage produced late in growing

season (one generation, larvae immobile)– Aggression towards conspecifics prevents decimation of

food supply

Competition

20062007

20082009

20102011

2012

010203040506070

Leaf area mined (%)

20062007

20082009

20102011

2012

02468

101214

Eggs per leaf

max n survivors

Initial number of larvae

Pro

babi

lity

of

indi

vidu

al s

urvi

val

Per

cent

of l

eaf

surfa

ce m

ined

Pup

al m

ass

(mg)

(a)

(b)

(c)

Est

imat

ed n

umbe

r su

rviv

ing

0.00.20.40.60.81.01.21.4

0.0

0.1

0.2

0.3

0.4

0.5

0

0.2

0.4

0.6

0.8

1

0 5 10 15

Pupal mass of survivors (mg)

Initial larvae per leaf Doak & Wagner in review

Competition

20062007

20082009

20102011

2012

010203040506070

Leaf area mined (%)

20062007

20082009

20102011

2012

02468

101214

Eggs per leaf

max n survivors

Initial number of larvae

Pro

babi

lity

of

indi

vidu

al s

urvi

val

Per

cent

of l

eaf

surfa

ce m

ined

Pup

al m

ass

(mg)

(a)

(b)

(c)

Est

imat

ed n

umbe

r su

rviv

ing

0.00.20.40.60.81.01.21.4

0.0

0.1

0.2

0.3

0.4

0.5

0

0.2

0.4

0.6

0.8

1

0 5 10 15

Pupal mass of survivors (mg)

Initial larvae per leaf

Intense interference competition:• Prevents food limitation• Allows some larvae to survive leaf

overpopulation• Preserves leaf function

Doak & Wagner in review

What ended the outbreak?

• Phenological mis-match• Adult overwintering survival• Egg mortality• Larval parasitism• Larval and pupal predation (ants, birds)• Larval and pupal mortality (other predators,

pathogens)

What ended the outbreak?

• Phenological mis-match• Adult overwintering survival• Egg mortality• Larval parasitism• Larval and pupal predation (ants, birds)• Larval and pupal mortality (other predators,

pathogens)

20062007

20082009

20102011

2012

Percent of individuals

0

20

40

60

80

100

Dead in leafRemovedParasitizedSurvived

What ended the outbreak?

20062007

20082009

20102011

20122013

Survivors per leaf

0.0

0.2

0.4

0.6

0.8

1.0

Indirect effect of WLBM increase?

Doak & Wagner in review

15

How does leaf mining affect aspen performance?

Methodology• Experimental suppression of leaf miner density on

aspen < 2m• 2 sites: Bonanza Creek and Ester Dome; mixed stands• 7 years

How does leaf mining affect aspen performance?

• Mortality– No effect of leaf miner suppression

• Growth and size– Strong effects

Effects of leaf mining across 7 years

2005 2012

Height (cm)

20

40

60

80

100

120

140

160

InsecticideControl

Wagner & Doak 2013

2005 2012

Diameter at 20 cm (mm)

6

8

10

12

14

16

18

20

Implications for browsing, competition

Mechanisms of ALM-caused aspen decline

• Early leaf abscission (Wagner et al. 2008)

• Leaf mining reduces photosynthesis by disrupting stomatal function (Wagner et al. 2008)

• Mining disrupts water balance (unpubl.)

• Mining induces ineffectual defenses– Phenolic glycosides (Young et al. 2007)

– Extrafloral nectar (Newman & Wagner 2013) – Both increase costs

Willow leaf blotch miner(Micrurapteryx salicifoliella)

Willow leaf blotch miner(Micrurapteryx salicifoliella)

One generation Multiple Salix hosts Larvae consume mesophyll Mobile – will move to new leaves within plant

Wide variation in susceptibility among willow species

Willow species

% Leaf mining

0

20

40

60

80

10020102011

Questions• What are the individual and combined effects of invertebrate

and vertebrate herbivores on the early successional plant community & ecosystem?

• Do invertebrate and vertebrate herbivore interact indirectly through effects on plants:– Production– Plant chemistry / palatability

• E.g. Summer insect leaf herbivory may affect availability or palatability of willow species preferred by mammals in winter

Experiment: Impact of, and interactions between, invertebrate & vertebrate herbivores

• Started spring 2012; ~10 year duration • Invertebrate suppression (insecticide) x exclusion of

moose/hares (fencing)• Dependent variables:

– Willow herbivory, browse, production, chemistry– Community composition– Soil nutrients, decomposition

Tanana River

Impact of, and interactions between, insect & vertebrate herbivores

• Preliminary results– Suppressing insect herbivory increased production

of woody tissues (~ 50% in 2012)– No notable changes in community composition– No evidence that insect herbivory wood chemistry– No effect of insect suppression on mammalian

browsing to date

Conclusions• Why did ALM outbreak last so long? Tolerance, intense interference competition

• What caused the end of the ALM outbreak? Increased larval and pupal mortality by biotic agent

• How does aspen leaf miner (ALM) affect plant performance? Weak effects on mortality; strong negative effects on plant size

• New experiment: Long term consequences of invertebrate herbivory, vertebrate browsing, and their interaction

Underway

Implications of insect outbreaks

• NPP

• Successional sequence

• Source of uncertainty in ecosystem projections