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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

bboeken@bgu.ac.ilhttp://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)