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• Crop pests• Insect herbivory• Natural pest management• Chemical control • Biological and ecological control• Transgenic technology
AgroecologyEcological understanding of farming systems
Ben-Gurion University of the Negev
7. Crop pest control
[email protected]://www.bgu.ac.il/desert_agriculture/Agroecology/Ó BBoeken 2005-18
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Crop pests• Herbivores
– Vertebrates– Insects– Mites– Nematodes
• Weeds– Competitors for
resources– Co-dispersers
• Diseases– Fungi– Bacteria– Viruses
Red Sunflower Weevilipmworld.umn.edu
Black Bean Aphidwww.inra.fr
Soybean Cyst Nematodenematode.unl.edu
Rose Mosaic Viruswww.huntingtonbotanical.org
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Insect herbivoryReduction of net yield
– NPP-consumption
– Damage to roots, foliage, flowers, fruits
– Disproportional reduction of market value
Species specificity– Generalists
– Specialists
Crop infestation– Plant density and
apparency
– Accessibility
Plant defense– Bottom-up control
– Structural protection
– Secondary compounds (quantitative/qualitative)
– Costs and benefits (defense-growth trade-off)
Aspergillus and insect damagewww.apsnet.org
Stamp, N. 2003. The Quarterly Review of Biology 78,23-55
Net Assimilation Rate
Relative Growth Rate
Secondary metabolism
– Defence and tolerance
– Genotypic or phenotypic expression
– Constitutive or inducible defense
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Insect predationTop-down control
• Predators– Vertebrate insectivoresBirds, lizards, shrews
Generalists
– Predatory insects (ladybugs, lacewings, beetles, mantises)
Specialists on common pests, inclsessile pests
(Aphids, scale insects, etc.)
– Spiders Generalists of moving prey, not sessile
insectsAlso of predators and
parasitoids
BlackbirdSannse en.wikipedia.org
• Parasitoids– Syrphid flies, ichneumonid wasps
Specialists on larvae and sessile insects
Parasitized by hyperparasites
• Pathogens– Fungi, bacteria, viruses
Host-specific
Araneus diadematusAndré Karwath en.wikipedia.org
Aleiodes indiscretus wasp parasitizing a gypsy moth
caterpillar. Scott Bauer en.wikipedia.org
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Natural enemies of cabbage
Graham Burnett, en.wikipedia.org
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Chemical insect control• Insecticides
– Heavy metals• Lead, mercury, arsenic
– Plant toxins• Nicotine, pyrethrum
– Organochlorines• DDT, Dieldrin, Lindane
– Organophosphates• Parathion, Malathion
• Advantages– No more insect damage– Quick and easy application
• Disadvantages– Selection of resistance– Increasing use– Kills all insects– Accumulates in food chain
• Causes thin egg shells in birds
– Spreads in the environment– Dangerous to handle
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Natural insect controlPredator efficiency• Consumption rate (A)• Consumer population response (B)• Food patch distribution (C)• Giving-up density
• Life-cycle synchrony• Availability, colonization• Prey-switching
www.agedstore.com
A. Functional response B. Numerical response
Food densityFood density
Feed
ing
rate
Con
sum
er d
ensi
ty
C. Ideal Free Distribution
Consumer density
Prof
itabi
lity
(Inta
ke ra
te)
Consumer aggregation
Food depletion
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Use of plant defenses– Repellants– Decoys– Low crop density– High genetic crop diversity
Ecological control
Physical means– Hand picking (large insects)– Solarization
• against weeds and soil nematodes• instead of herbicides and Methylbromide
Pyrethrum field www.dpiwe.tas.gov.au
Colorado potato beetle en.wikipedia.org
Enhancement of natural predators • Landscape diversity (habitats)• Nesting sites, refugia• Alternative prey
http://www.simplynaturalorganic.com
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Augmentation of natural enemiesand introduction of exotics
(Risk of invasiveness!)
• Weed herbivores– Aphthona lacertosa (feeds on leafy spurge roots)
• Predators– Rodolia cardinalis on cottony cushion scale
• Parasitoids– Ichneumonoid wasps (oviposit in aphids)
• Parasites– Nematodes (Phasmarhabditishermaphrodita on slugs)
• Pathogens– Fungus (Trichoderma viride)
• Toxic bacteria – Bacillus thuringiensis (Bt)
(toxic if ingested)
Biological control
Aphthona lacertosa, an introduced root-feeding flea beetle.
Icerya purchasi - Infestation of citrus plantations in California, 1888(http://www.bugwood.org)
The predator, Vestalia ladybird -Rodolia cardinalis, from Australia (http://www.ento.csiro.au/)
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Transgenic plants (GMOs)• Bt plants
– Insertion of Bt plasmid into crop plant genome– Specific Bt plasmid for particular pest– Insect herbivores die upon ingestion– Low chance of resistance
• Advantages– Yield increase due to absence of herbivory– No use of chemical pesticides– Presumably no effect on non-pest insects
and higher trophic levels (?)
Bacillus thuringiensisJDeacon helios.bto.ed.ac.uk
• Other applications in plants– Vitamin A production– Roundup–ready crops
• Broad toxicity and bio-accumulation• Resistance leading to superweeds
– �Terminator� genes• Sterile second generation
http://cls.casa.colostate.edu/TransgenicCrops/index.html
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Problems of GMOs
See also the Convention on Biological Diversity,Rio de Janeiro 1992 (http://www.cbd.int/)
• Ineffective on sucking insects – Mirid leaf bugs on Bt-cotton– New insect pest
• Possible adverse effects on insect diversity
– Pollen-eating non-target insects(on Bt-corn, Zangerl et al. 2001)
– Pollinators
• Low crop diversity– Few cultivars used for technique– Regional crop diversity threatened • Societal issues
– Dependence on few large companies– Legal aspects (patents on GMOs!)– Package deals with other products – Corporate business monopoly– Human health concerns
Potato diversity, Peru
(http://nissa.ger-nis.com)