Arthropod Communities In Temperate Agroforestry: Theory and Reality W. Terrell Stamps, Terry L. Woods Robert L. McGraw, and Marc J. Linit Division of Plant

Arthropod Communities In Temperate Agroforestry:

Theory and Reality

W. Terrell Stamps, Terry L. WoodsRobert L. McGraw, and Marc J. Linit

Division of Plant Sciences & UM Center for AgroforestryUniversity of Missouri, Columbia, MO, USA

Temperate versus Tropical Agroforestry

Differ in almost every respectEnvironment – soil, climate, topographyPlant speciesArthropod species – pests and beneficialsDesign and management

Do theories of biodiversity proven from the tropics translate to temperate agroforestry practices?

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 matterSpecies-area relationship and the equilibrium theory of island biogeography more area, more species (Connor and McCoy 1979,

MacArthur and Wilson 1967).


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


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

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 Hypothesis

Complex Systems

refugia prey variety

prey abundance nectar and pollen

Cue disruption host finding rates

Complex Systems



Cue disruption host finding rates

Simple Systems



No cue disruptionNo effect

Simple Systems



No cue disruptionNo effect

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 ConcentrationHypothesis

Complex Systems

Less apparent emigration visual cues

Chemical cue disruption

Food sources

Complex Systems

Less apparent emigration visual cues

Chemical cue disruption

Food sources

Simple Systems

More apparent emigration visual cues

Chemical cues

Single food source

Simple Systems

More apparent emigration visual cues

Chemical cues

Single food source

Arthropod Communities in Temperate Agroforestry: The Reality

Crop Polyculture vs MonocultureConsiderable evidence of the positive effects of multiple plant systems

Forestry Polyculture vs MonocultureFewer studies - some evidence of positive effects

Agroforestry vs Traditional AgricultureStudies are lacking

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

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

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

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 2

Alley cropped

Monocropped

Project 1

Alley cropped

Monocropped

Project #3, SW Missouri, USA

Monocropped

12 M (40 ft) Alleyways

24 M (80 Ft) Alleyways

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

SamplingSweeps down the center of plots

Pitfall traps diagonal across plots

Herbivore Individuals in Alfalfa: Agroforestry vs. Conventional Plots

0

50

100

150

200

300

500

1997 1998

# I n

di v

idu

a ls

AC alfalfa (left bars) MC alfalfa (right bars)

a b a b

Predator Individuals in Alfalfa: Agroforestry vs. Conventional Plots

0

5

10

15

30

1997 1998

AC alfalfa (left bars) MC alfalfa (right bars)

PredatorsPredatorsa b a b

ParasiticHymenops

a bParasitic

Hymenops

a a

# I n

di v

idu

als

Diversity Indices

Index Alley cropped Monocropped

Shannon (H’) 1.8 + 0.4a 1.6 + 0.4bSimpson (1/D) 5.0 + 2.1a 3.8 + 1.7bEvenness (E) 0.7 + 0.2a 0.6 + 0.2b

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

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 yields4 reps each

SamplingMultiple sweep samples down a central transectCollect pest samples for parasitoid activityAlfalfa sampling for quality / yield

Study #2 Initial Alfalfa GrowthApril 2001

Alley cropped

Monocropped

Arthropods in Alfalfa: Agroforestry vs. Conventional Plots

Parasitic Hymenoptera

a

b

Predators

a a

Herbivores

a b

MC alfalfa (right bars)

0

5

10

15

20

25

30

35

AC (left bars)

# I n

di v

idu

als

0

100

200

300

400

Alfalfa Weevil Larvae Mortality (%)

Alley Cropped Monocropped

Healthy AWA 35 + 14a 42 + 12aBathyplectes 46 + 10a 37 + 14bZoophthora 17 + 5a 11 + 11aNematode 1 + 2a 1 + 2aUnk Mortality 2 + 2a 11 + 9b Total Parasitism 63 + 12a 48 + 9b

aa

Yields over the season

0

100

200

300

400

500

Dry

Wei

gh

t ( g

m/ m

2 )

September CuttingJune CuttingMay Cutting

b ba

b

Alley cropped (AC) Monocropped (MC)

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

Study #3, 12/24 M alleyways, Early Spring

12 M alleyways

Monocropped

Study #3, 12/24 M alleyways, Early Spring

24 M alleyway

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

Treatment Herb taxa Herb individ


12 M alley 8 + 2a 45 + 16a

24 M alley 7 + 2a 43 + 9a

Predator taxa and individuals in AC and MC alfalfa

Treatment Pred taxa Pred individ


12 M alley 8 + 3b 10 + 4b

24 M alley 7 + 1b 9 + 3b

Parasitic hymenoptera taxa and individuals in AC and MC alfalfa

Treatment Para taxa Para individ


12 M alley 4 + 2b 5 + 2b

24 M alley 4 + 1b 5 + 2b

Alfalfa Weevil Larvae Mortality (%)31 March 2004

Monocrop 12 M alley 24 M alley

Healthy AW 48 + 10a 44 + 14a 45 + 4aBathyplectes 38 + 14a 25 + 11a 28 + 9aZoophthora 15 + 6a 31 + 15b* 33 + 7bNematode --- --- ---

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

Higher fungal parasitism in the alleyways

Alfalfa Weevil Larvae Mortality (%)16 April 2004


Healthy AW 41 + 12a 19 + 11b 26 + 7bBathyplectes 29 + 16a 30 + 24a 16 + 3aZoophthora 30 + 4a 51 + 32b* 58 + 9bNematode --- --- ---

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

Higher fungal parasitism in the alleyways, fewer adults



Healthy AW 73 + 13a 53 + 13b 59 + 6bBathyplectes 10 + 8a 33 + 9b 27 + 20bZoophthora 17 + 5a 14 + 5a 17 + 10aNematode --- --- 2 + 5

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

Higher bathy parasitism in the alleyways, fewer adults



Healthy AW 13 + 13a 3 + 5a 5 + 5aBathyplectes 14 + 12a 38 + 8b 19 + 15aZoophthora 74 + 20a 57 + 6b 74 + 13aNematode --- 2 + 5 ---

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

Fungal epizootic killed most of the larvae

a bba

cb

Yield over the Season (Study 2)

a0

100

200

300

400

500

Dry

Wei

gh

t ( g

m/ m

2 )

September CuttingJune CuttingMay Cutting

b

AC12 AC24

b

Open

Conclusions

Reality seems to follow theory, so farMore 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?

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 numerousIncreased plant diversity

Increased arthropod diversity

Environmentally sound, sustainable practice

Thanks to:

Jimmy HouxAaron BrownMelissa NiedermannMike GoldHarold “Gene” Garrett

These projects are funded by: USDA ARS Cooperative Agreements

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

Documents

Arthropod Communities In Temperate Agroforestry: Theory and Reality W. Terrell Stamps, Terry L. Woods Robert L. McGraw, and Marc J. Linit Division of Plant