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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
2
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
3
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
4
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
5
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
6
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
8
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
9
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)
11
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!
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