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Arthropod Communities In Temperate Agroforestry: Theory and Reality. W. Terrell Stamps, Terry L. Woods Robert L. McGraw, and Marc J. Linit Division of Plant Sciences & UM Center for Agroforestry University of Missouri, Columbia, MO, USA. Temperate versus Tropical Agroforestry.

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arthropod communities in temperate agroforestry theory and reality

Arthropod Communities In Temperate Agroforestry:Theory and Reality

W. Terrell Stamps, Terry L. Woods

Robert L. McGraw, and Marc J. Linit

Division of Plant Sciences & UM Center for Agroforestry

University of Missouri, Columbia, MO, USA

temperate versus tropical agroforestry
Temperate versus Tropical Agroforestry
  • Differ in almost every respect
    • Environment – soil, climate, topography
    • Plant species
    • Arthropod species – pests and beneficials
    • Design and management
  • Do theories of biodiversity proven from the tropics translate to temperate agroforestry practices?
insect diversity in agroecosystems the theory
Insect Diversity in Agroecosystems:The Theory
  • Animal diversity correlates with plant diversity(Murdoch et al. 1972)
    • The tropics as an example.
  • Temporal and structural diversity increases arthropod diversity
    • Trees harbor more a diverse community than herbaceous plants (Lawton and Schroder 1977, Strong and Levin 1979, Niemala et al. 1982).
  • Size does matter
    • Species-area relationship and the equilibrium theory of island biogeography  more area, more species (Connor and McCoy 1979, MacArthur and Wilson 1967).
insect diversity in agroecosystems the theory4
Insect Diversity in Agroecosystems:The Theory
  • Within-field vegetation diversity reduces pest populations
    • E.g. intercropped systems  pests compared to monocropped systems
  • Many theories involving all aspects of the ecology of the system have been proposed
insect diversity in agroecosystems the theory5
Insect Diversity in Agroecosystems:The Theory
  • Associational Resistance Theory

(Tahvanainen and Root 1972)

Multispecies plant associations have a synergistic interaction that reduces insect damage compared to single species plant systems.

    • Enemies Hypothesis
    • Resource Concentration Hypothesis
    • Appropriate-Inappropriate Landing Hypothesis
    • Host Plant Quality Hypothesis
enemies hypothesis
Enemies Hypothesis

Predicts that natural enemies will be more abundant in complex systems vs simple systems, and that their action will result in lower herbivore population densities

enemies hypothesis7
Enemies Hypothesis

Complex Systems

 refugia

 prey variety

 prey abundance

 nectar and pollen

Cue disruption

 host finding rates

Simple Systems

 refugia

 prey variety

 prey abundance

 nectar and pollen

No cue disruption

No effect

resource concentration hypothesis
Resource Concentration Hypothesis

Predicts that insect herbivores are more likely to locate and remain on host plants that occur in large, dense, pure stands

resource concentration hypothesis9
Resource ConcentrationHypothesis

Complex Systems

Less apparent

 emigration

 visual cues

Chemical cue disruption

 Food sources

Simple Systems

More apparent

 emigration

 visual cues

 Chemical cues

Single food source

arthropod communities in temperate agroforestry the reality
Arthropod Communities in Temperate Agroforestry: The Reality
  • Crop Polyculture vs Monoculture
    • Considerable evidence of the positive effects of multiple plant systems
  • Forestry Polyculture vs Monoculture
    • Fewer studies - some evidence of positive effects
  • Agroforestry vs Traditional Agriculture
    • Studies are lacking
our studies
Our Studies
  • Ecological theories predict↑ biodiversity and improved management of insect pests in agroforestry versus conventional agriculture
  • We are examining the impact of agroforestry alley cropping practices on insect populations
objectives of our research
Objectives of our Research
  • Is arthropod diversity greater in alley cropped alfalfa than in conventionally grown alfalfa?
  • Are pests less abundant and natural enemies more abundant in an agroforestry setting
  • Economics - Is crop quality and quantity affected and can pesticide use be reduced?
eastern black walnut juglans nigra
Eastern Black Walnut, Juglans nigra
  • Valued for both the nut crop and the wood
  • Adds “sustainability” to agricultural practices
  • May provide ecological benefits when added to traditional

agricultural practices

alfalfa medicago sativa
Alfalfa, Medicago sativa
  • 4th most widely grown crop in U.S.
  • Very high nutritional quality – used for feed
    • Commercial hay production
    • Dairy and beef cattle
    • Horses, sheep, goats
  • Prone to pest problems
    • Chemical controls
    • Mechanical controls
project 1 project 2 sw missouri sho neff plantation
Project #1 & Project #2 SW Missouri – Sho-Neff Plantation

Project 2

Alley cropped

Monocropped

Project 1

Alley cropped

Monocropped

project 3 sw missouri usa
Project #3, SW Missouri, USA

Monocropped

24 M (80 Ft) Alleyways

12 M (40 ft) Alleyways

study 1 alfalfa brome alley cropped with black walnut
Study #1 Alfalfa & brome alley croppedwith black walnut
  • “Pilot study”
    • small plots (12 M x 36 M)
    • small monocrop area, few control plots
    • Alfalfa, smooth bromegrass and vegetation-free alleyways included
  • Sampling
    • Sweeps down the center of plots
    • Pitfall traps diagonal across plots
herbivore individuals in alfalfa agroforestry vs conventional plots
Herbivore Individuals in Alfalfa: Agroforestry vs. Conventional Plots

AC alfalfa (left bars)

MC alfalfa (right bars)

500

300

200

# Individuals

150

100

50

a

a

b

b

0

1997

1998

predator individuals in alfalfa agroforestry vs conventional plots

a

b

a

b

a

b

a

a

Predators

Parasitic

Hymenops

Parasitic

Hymenops

Predator Individuals in Alfalfa: Agroforestry vs. Conventional Plots

AC alfalfa (left bars)

MC alfalfa (right bars)

30

15

# Individuals

10

5

0

Predators

1997

1998

diversity indices
Diversity Indices

Index Alley cropped Monocropped

Shannon (H’) 1.8 + 0.4a1.6 +0.4b

Simpson (1/D) 5.0 +2.1a3.8 +1.7b

Evenness (E) 0.7 +0.2a0.6 +0.2b

study 1 conclusions
Study #1 Conclusions
  • 2X as many natural enemies in alley cropped alfalfa
  • ½ as many herbivores in alley cropped alfalfa
  • Arthropod community more diverse and even in alley cropped alfalfa
studies 2 3
Studies #2 & #3
  • Study 2: 12 M (40 ft) alleyways versus traditionally-grown alfalfa
    • ½ acre reps – 4 alley cropped, 4 monocropped
  • Study 3: 12 M and 24 M (80 ft) alleyways versus traditionally-grown alfalfa
    • Wider alleys to improve crop yields
    • 4 reps each
  • Sampling
    • Multiple sweep samples down a central transect
    • Collect pest samples for parasitoid activity
    • Alfalfa sampling for quality / yield
arthropods in alfalfa agroforestry vs conventional plots

MC alfalfa (right bars)

AC (left bars)

Arthropods in Alfalfa: Agroforestry vs. Conventional Plots

400

35

30

300

25

20

# Individuals

200

15

10

100

b

5

a

a

a

a

b

0

0

Parasitic Hymenoptera

Predators

Herbivores

alfalfa weevil larvae mortality
Alfalfa Weevil Larvae Mortality (%)

Alley Cropped Monocropped

Healthy AWA 35 +14a 42 +12a

Bathyplectes 46 +10a 37 +14b

Zoophthora 17 + 5a 11 +11a

Nematode 1 + 2a 1 + 2a

Unk Mortality 2 + 2a 11 + 9b

Total Parasitism 63 + 12a 48 + 9b

slide26

Yields over the season

Alley cropped (AC)

Monocropped (MC)

500

400

300

Dry Weight (gm/m2)

200

a

100

a

a

b

b

b

0

June Cutting

September Cutting

May Cutting

study 2 conclusions
Study #2 Conclusions
  • Arthropod communities more diverse in AC alfalfa than in MC alfalfa (trend, not significant)
  • AC alfalfa has fewer herbivores and more parasitic hymenoptera than MC alfalfa
  • Higher rates of parasitism of AWL in AC alfalfa vs MC alfalfa
  • Poor yields in alleyways
taxa and individuals in ac and mc alfalfa
Taxa and individuals in AC and MC alfalfa

Treatment Total taxa Total individ

Monocrop 15 + 3a 64 + 19a

12 M alley 22 + 4b 84 + 22b

24 M alley 19 + 4b 84 + 14b

herbivore taxa and individuals in ac and mc alfalfa
Herbivore taxa and individuals in AC and MC alfalfa

Treatment Herb taxa Herb individ

Monocrop 7 + 2a 38 + 10a

12 M alley 8 + 2a 45 + 16a

24 M alley 7 + 2a 43 + 9a

predator taxa and individuals in ac and mc alfalfa
Predator taxa and individuals in AC and MC alfalfa

Treatment Pred taxa Pred individ

Monocrop 4 + 2a 5 + 3a

12 M alley 8 + 3b 10 + 4b

24 M alley 7 + 1b 9 + 3b

parasitic hymenoptera taxa and individuals in ac and mc alfalfa
Parasitic hymenoptera taxa and individuals in AC and MC alfalfa

Treatment Para taxa Para individ

Monocrop 2 + 1a 2 + 1a

12 M alley 4 + 2b 5 + 2b

24 M alley 4 + 1b 5 + 2b

alfalfa weevil larvae mortality 31 march 2004
Alfalfa Weevil Larvae Mortality (%)31 March 2004

Monocrop 12 M alley 24 M alley

Healthy AW 48 +10a 44 +14a 45 +4a

Bathyplectes 38 +14a 25 +11a 28 +9a

Zoophthora 15 + 6a 31 +15b* 33 +7b

Nematode --- --- ---

Total Para 53 + 10a 56 +14a 55 +4a

  • Higher fungal parasitism in the alleyways
slide35

Alfalfa Weevil Larvae Mortality (%)16 April 2004

Monocrop 12 M alley 24 M alley

Healthy AW 41 +12a 19 +11b 26 +7b

Bathyplectes 29 +16a 30 +24a 16 +3a

Zoophthora 30 + 4a 51 +32b* 58 +9b

Nematode --- --- ---

Total Para 59 +10a 81 +11b 74 +8a

  • Higher fungal parasitism in the alleyways, fewer adults
slide36

Alfalfa Weevil Larvae Mortality (%)4 April 2005

Monocrop 12 M alley 24 M alley

Healthy AW 73 +13a 53 +13b 59 +6b

Bathyplectes 10 +8a 33 +9b 27 +20b

Zoophthora 17 +5a 14 +5a 17 +10a

Nematode --- --- 2 +5

Total Para 27 +13a 48 +13b 42 +11b*

  • Higher bathy parasitism in the alleyways, fewer adults
slide37

Alfalfa Weevil Larvae Mortality (%)18 April 2005

Monocrop 12 M alley 24 M alley

Healthy AW 13 +13a 3 +5a 5 +5a

Bathyplectes 14 +12a 38 +8b 19 +15a

Zoophthora 74 +20a 57 +6b 74 +13a

Nematode --- 2 +5 ---

Total Para 88 +13a 95 +6a 93 +9a

  • Fungal epizootic killed most of the larvae
slide38

Yield over the Season (Study 2)

AC12

AC24

Open

500

400

300

Dry Weight (gm/m2)

200

a

100

a

b

b

a

b

b

b

c

0

June Cutting

September Cutting

May Cutting

conclusions
Conclusions
  • Reality seems to follow theory, so far
    • More diverse arthropod community in the more diverse agroforestry practice vs monocrop
    • Evidence for Enemies Hypothesis
      • More predators and parasitic hymenoptera in AC alfalfa vs MC alfalfa
      • Higher parasitism rates of alfalfa weevil in AC alfalfa vs MC alfalfa
    • Impact on the economics still to be determined, but yield in the wider alleyways looks promising
recommendations
Recommendations?
  • Don’t grow alfalfa in 40 ft alleyways
  • Consider growing alfalfa in the center 60 ft of 80 ft alleyways
  • Impact on pest management unknown, but promising
  • “Intangible” environmental benefits numerous
    • Increased plant diversity
    • Increased arthropod diversity
    • Environmentally sound, sustainable practice
slide41

Thanks to:

Jimmy Houx

Aaron Brown

Melissa Niedermann

Mike Gold

Harold “Gene” Garrett

These projects are funded by:

USDA ARS Cooperative Agreements

58-6227-0-049 & 58-6227-1-004

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