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Plant Diversity and It’s Influence on Beneficial Insects

Paula Shrewsbury, Ph.D.Department of Entomology

University of Marylandpshrewsbury@umd.edu

Montgomery County Master GardenersJune 4, 2009

Pests outbreak more frequently in managed than natural ecosystems

Why do insects become “pests” in managed landscapes?

• Use of pest susceptible plant material

• Unwise planting design

• Improper installation and maintenance of plants

• Disruption of natural enemy communities

Euonymus scale on Euonymus

Hawthorn lace bug on cotoneaster

Banded Ash Clearwing Borer

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Peachtree Borer Hemlock Wooly Adelgid

Adelgid Survival Number of Eggs Biomass N.G.0

50

100

150

200

250

Surv

ival

(%),

Eggs

, or B

iom

ass

Effects of Fertilzer on Adelgids and Hemlocks

Control Before Infest. At Infest.

McClure 1991 Image by M. Raupp, UMD

Goal• Create and maintain sustainable urban systems

Need to give natural enemies a helping hand

Restore natural enemy – herbivore dynamics and ecological function

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Biological Control• Relies on natural enemies, the predators, parasitoids, and pathogens capable of reducing pest insects and mites to tolerable levels

Conservation Biological Controlthe deliberate attempt to maintain beneficial organisms in the nursery or landscape habitat

1. avoidance of activities that are harmful to or disrupt natural enemies

2. enhancement of the habitat to promote natural enemy survival and reproduction, and to attract and retain natural enemies

How does low diversity affect ecosystem function?

Diversity can be estimated different ways

•Species richness - number of plant species

•Habitat structural complexity – vegetation found in a three dimensional space

What is the relationship between plant species richness and the diversity of arthropod pests in residential landscapes?

Low plant diversity n = 3 species

High plant diversity n = 34 species

(212 landscapes examined, Raupp et al. 2001)

0 5 10 15 20 25 30 35 40

Number of Plant Species

0

5

10

15

20

25

Num

ber o

f Arth

ropo

d Pe

st S

peci

es Relationship Between the Number ofPlant and Arthropod Pest Species

P< 0.001, r 2=0.18

Raupp et al. 2001

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Plant species diversity increases the number of pest species in landscapes, but can diversity save us in the end?

ground cover or turfherbaceous plants

shrubs

understory

overstory

Habitat structural complexity

Shrewsbury and Raupp 2000, Environmental Entomology

Structural comlexity = 70

Structural comlexity = 225

Azalea Lace BugStephanitis pyrioides

www.hort.cornell.edu

Habitat Structural ComplexitySimple Complex

Simple Complex0

100200300400500600700800900

Num

ber o

f Lac

e B

ugs

Abundance in simple and complex landscapes

Shrewsbury and Raupp 2000, Environmental Entomology

Why a 100 fold difference in abundance of lace bugs?

• Host plant quality

• Lace bug movement

• Natural enemies

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Predator group or taxa Simple Complex PGeneralist predators (total) 13.1 ± 2.6 21.8 ± 2.6 0.0273

Spiders (total) 24.7 ± 5.2 40.6 ± 5.4 0.0467

Anyphaenidae (foraging spider) 4.93 ± 1.1 25.0 ± 2.5 0.0001

Thomisidae (crab spider) 1.58 ± 1.1 8.31 ± 2.9 0.0029

Theridiidae (web spider) 9.28 ± 3.7 2.63 ± 0.7 0.0799

Oxyopidae (foraging spider) 3.64 ± 2.2 0.68 ± 0.2 0.1111

Salticidae (jumping spider) 3.97 ± 1.2 2.31 ± 1.0 0.2976

Phalangidae (daddy long leg) 0.38 ± 0.2 1.32 ± 0.4 0.0612

Gryllinae (field cricket) 1.36 ± 0.7 6.63 ± 1.8 0.0010

Oecanthinae (snowy tree cricket) 0.27 ± 0.2 1.73 ± 0.6 0.0139

Forficulidae (earwigs) 1.14 ± 0.5 1.24 ± 0.3 0.8720

Formicidae (ants) 4.72 ± 1.5 6.44 ± 1.4 0.4185

Miridae (plant bugs) 0.27 ± 0.1 0.02 ± 0.0 0.0140

Survival of lace bug cohorts – exposed to natural enemies

Cage No Cage Cage No Cage0

2

4

6

8

10

Num

ber o

f alb

Coh

orts

Dis

appe

arin

g

Complex Simple

a

b

c c

Shrewsbury and Raupp 2006, Ecological Applications

Lace BugsNatural Enemies

Lace Bugs

Natural Enemies

Why are there more predators and greater predator pressure in complex landscape habitats?

Natural enemies can be -• Generalists – feed on a wide range of prey

• Specialists – feed on only one or a few species of prey

• Omnivores – feed on both animals (prey) and plants (pollen, nectar)

Images by M.RauppP.Shrewsbury

M. Raupp

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Structural Complexity

Plant Diversity

RefugesMicroclimatesAlternative food sources(prey, nectar, pollen)

0 5 10 15 20 25 30 35 40

Number of Plant Species

0

5

10

15

20

25

Num

ber o

f Arth

ropo

d Pe

st S

peci

es Relationship Between the Number ofPlant and Arthropod Pest Species

P< 0.001, r 2=0.18

Raupp et al. 2001

Why are there more predators and greater predator pressure in complex landscape habitats?

Additional food sources – alternative prey-Coriandrum sativum and Chrysanthemum maximum, increased alternative prey and n.e. abundance and reduced survival of Stephanitis pyrioides – Shrewsbury, Lashomb, Hamilton, Zhang, Patt, Casagrande

- Lobularia maritima, Coreopsis verticillata, and Panicum virgatum increased alternative prey and n.e. abundance and reduced survival of Agrotis ipsilon - Frank and Shrewsbury

Simple Complex0

102030405060708090

100

Num

ber o

f Alte

rnat

ive

Prey

Abundance in simple and complex landscapesComplex landscapes have more alternative prey

0 5 10 15 20 25 30 35 40 45 50 55 60

Number of Alternative Prey

0

1

2

3

4

5

6

7

Num

ber o

f Spi

ders

Do important predators respond to variation in prey abundance?

Shrewsbury and Raupp 2006, Ecological Applications

Lace BugsNatural Enemies

Alternative Prey

Lace Bugs

Natural EnemiesAlternative Prey

Habitat ComplexitySimpleComplex

Is it possible to design or create landscapes with increased complexity and reduce pest abundance?

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Add flowers

to landscapes

Shrewsbury et al. 2004, IJEES

Shasta Daisy•Warm season bloomer

•Large floral architecture

Coriander

•Cool season bloomer

•Small floral architecture

Conclusions:

Azaleas plots with flowers have:• greater abundance of alternative prey• greater abundance of natural enemies• lower survival of azalea lace bug

Why are there more predators and greater predator pressure in complex landscape habitats?

Additional food sources – floral resources-Peonia lactiflora increased parasitism by Tiphia vernalis, Rogers and Potter

-Trifolium repens, Euphorbia epithymoides, Coreopsis verticillata, and Solidagocanadensis increased abundance of n.e. – Rebek, Hanks, Sadof

-15 spp. wildflowers increased abundance of n.e. -Braman, Pendley, Corley

-Coriandrum sativum and Chrysanthemum maximum, increased abundance of n.e. and reduced survival of Stephanitis pyrioides – Shrewsbury, Lashomb, Hamilton, Zhang, Patt, Casagrande

- Lobularia maritima, Coreopsis verticillata,and Panicum virgatum increased abundance of n.e. and reduced survival of Agrotis ipsilon – Frank and Shrewsbury

Conservation strips in Golf Courses

Tee

Green

Fairway Rough

Frank and Shrewsbury 2004, Enviromental Entomololgy

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Plants

Sweet Alyssum

Coreopsis Turfgrass-rough and fairway

Switchgrass

Why those

plants?

• Previous research• Season long bloom• Varying architectural complexity (floral and

structural)• Aesthetically pleasing• Deer proof• Low levels of herbivore feeding injury

Alyssum

Bunch Grass

Coreopsis

Control Plot

Rough

Fairway

Treatment Plot

>7m

2m

>60m

Circles indicate pitfall trap positions

3m

12m

6m

4m2m*0m*

8m

12m

6m

4m2m0m

8m

Conservation strip

Ground beetles, Rove beetles, and Spiders

Alyssum

Bunch Grass

Coreopsis

Control Area

Rough

Fairway

Treatment Area

>7m

2m

>60m

Circles indicate Black Cutworm positions

6m*

2m

0m

10m*

6m

2m

0m

10m

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Greater predation of cutworms in fairways Greater predation of cutworms in fairways with conservation strips than withoutwith conservation strips than without

Conservation strips show potential as a pest management tool on golf courses

Nursery EcosystemsDepauperate of natural enemies

P. Shrewsbury, UMD

P. Shrewsbury, UMD

Habitat manipulations to conserve natural enemies - creating sustainability

• Nursery manipulations

– Adding complexity and diversity

• Flowering plants, grasses, cover crops

• Hardwood mulch groundcover

How can we give natural enemies a helping hand? Enhance Beneficials by Providing Nectar and Pollen Sources• Carrot family (Umberlliferae)

– caraway, dill, fennel, coriander, parsley• Mint family (Labiatae)

– catnip, hyssop, lemon balm• Rosemary, thyme, other herbs• Daisy family (Compositae)

– coneflower, daisies, yarrow• Cover crops – use as garden borders

– alfalfa, buckwheat, clover• From: Organic Gardeners Handbook of Natural Insect and Disease Control.

1992. Rodale Press, Emmaus, PA.

Others: Sweet alyssum, phacelia, sunflower

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Publication: Farmscaping to Enhance Biological Control

http://www.attra.ncat.org/attra-pub/pdf/farmscaping.pdf

Google: attra

www.croatianworld.net

Shrubs & TreesBlackberry (Rubus)

Red maple (Acer rubrum)Dogwood (Cornus)

Raspberry (Rubus)Fruit trees (apple, cherry,

plum) Sumac (Rhus)

Juneberry (Amalanchier) Willows (Salix)

http://www.attra.org/attra-pub/pdf/farmscaping.pdf

bp2.blogger.com bp2.blogger.com

Flowers & HerbsAlfalfa (Medicago sativa)

Goldenrod (Solidago)Alsike clover (Trifolium hybridum) Goldfields (Lasthenia chrysostoma)

Asters (Aster) Hollyhock (Alcea rosea) (single varieties)

Beard tongue (Penstemon) Impatiens (Impatiens)Bee balm (Monarda)

Milkvetch (Astragalus)Birds-foot trefoil (Lotus corniculatus)

Milkweed (Asclepias)Borage (Borago officianalis)

Mints (Mentha, Salvia)Buttercup (Ranunculus) Marjoram (Origanum)

Calendula (Calendula) (single varieties) Nasturtiums (Tropaeolum)

http://www.attra.org/attra-pub/pdf/farmscaping.pdf

blogs.chron.com/lazygardener

Flowers & HerbsConeflower (Echinacea)

Oilseed rape (Brassica napus)Chrysanthemum (Dendranthema)

Pincushion (Chaenactis)Crown-beard (Verbesina)

Red clover (Trifolium pratense)Daisies Scorpion weed (Phacelia)Dandelion (Taraxacum officinale)

Sunflowers (Helianthus)Evening primrose (Oenothera)

Tickseed (Coreopsis)Forget-me-not (Myosotis) Wild mustard (Brassica)

Fuchsia (Fuchsia) Vervain (Verbena)

Gilia (Gilia) Wild buckwheat (Eriogonum)Globe mallow (Sphaeralcea)

http://www.attra.org/attra-pub/pdf/farmscaping.pdf

www.youcanlearnseries.com

Frank, Shrewsbury, & Esiekpe, 2008 Environmental Entomology (37:2)

MD Native plant species tested to determine their attractiveness to natural enemies

Common name Scientific name Family

Common milkweed Asclepias syriaca AsclepiadaceaeButterfly weed Asclepias turberosa AsclepiadaceaeThreadleaf coreopsis Coreopsis verticillata Asteraceae *Hyssopleaf thoroughwort Eupatorium hyssopifolium Asteraceae *Spotted horsemint Monarda punctata Lamiaceae *Narrowleaf mountain mint Pycnanthemum tenuifolium Lamiaceae *Skullcap Scutelaria integrifolia LamiaceaeSwitchgrass Panicum virgatum PoaceaeIndiangrass Sorghastrum nutans PoaceaeLittle bluestem Schizachyrium scoparium Poaceae

Frank, Shrewsbury, & Esiekpe, 2008 Environmental Entomology (37:2)

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www.croatianworld.net

Coreopsis verticillata

Eupatorium hyssopifolium

www.ct-botanical-society.org

Monarda punctata

groups.ncf.edu

Pycnanthemum tenuifolium

www.ct-botanical-society.org

“Winners” -MD Native Insectary

Plants

Frank, Shrewsbury, & Esiekpe, 2008 Environmental Entomology (37:2)

Fiedler and Landis 2007 Environmental Entomology (36:4)

http://nativeplants.msu.edu/pdf/E2973.pdf

www.sel.barc.usda.gov

magickcanoe.com

Recommendations:

• Increase structural complexity– More plants at different vegetational strata, especially tree and ground cover

layers

• Increase biodiversity– More plant species, families

• Add flowers– vary architectural complexity– provide season long bloom

• Select based on proven attractiveness and natural enemies they attract

• To provide:– a community of plant species that attracts diverse natural enemy taxa

and provides habitat, and nectar and pollen throughout the season

• Encourage and conserve beneficials

• Restore ecological function

• Prevent pests from outbreaking

• Create more sustainable managed systems

www.californiagreensolutions.com

THANK YOU!