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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.

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Arthropod Communities In Temperate Agroforestry: Theory and Reality

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  1. 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

  2. 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?

  3. 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).

  4. 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

  5. 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

  6. 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

  7. 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

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

  9. 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

  10. 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

  11. 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

  12. 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?

  13. 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

  14. 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

  15. Project #1 & Project #2 SW Missouri – Sho-Neff Plantation Project 2 Alley cropped Monocropped Project 1 Alley cropped Monocropped

  16. Project #3, SW Missouri, USA Monocropped 24 M (80 Ft) Alleyways 12 M (40 ft) Alleyways

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. Study #2 Initial Alfalfa GrowthApril 2001 Alley cropped Monocropped

  24. 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

  25. 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

  26. 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

  27. 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

  28. Study #3, 12/24 M alleyways, Early Spring Monocropped 12 M alleyways

  29. Study #3, 12/24 M alleyways, Early Spring 24 M alleyway

  30. 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

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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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