Cabbage Integrated Pest Management : An Ecological Guide.

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Ecology of Insect Pests and Natural Enemies4.7 The Friends of the FarmerNatural enemies are the friends of the farmer because theyhelp the farmer to control insect pests (herbivores) on cabbageplants. Natural enemies are also called beneficials, or biocontrolagents, and in case of fungi, antagonists. In countries like Bangladesh,natural enemies are called crop defenders.Most natural enemies are specific to a pest insect. Some insectpests are more effectively controlled by natural enemies than others.Natural enemies of insect pests can be divided into a few largergroups: predators, parasitoids, pathogens, and nematodes. Nematodes are oftenlumped together with pathogens. Some of the main characteristics of naturalenemies of insect pests are listed below. The major natural enemies of cabbageinsect pests are described in more details in chapter 6. Antagonists, naturalenemies of plant diseases, are described in section 7.10.CHARACTERISTICS OF NATURAL ENEMIES OF INSECT PESTS:Predators· Common predators are spiders, lady beetles, ground beetles, and syrphid flies.· Predators usually hunt or set traps to catch a prey to feed on.· Predators can feed on many different species of insects.· Both adults and larvae/nymphs can be predators.· Predators follow the insect population by laying more eggs when there is more preyavailable.Parasitoids· Parasitoids of cabbage pests are commonly wasps or flies.· Attack only one insect species or a few closely related species.· Only the larvae are parasitic. One or more parasitoid larvae develop on or inside asingle insect host.· Parasitoids are often smaller than their host.Pathogens· Insect-pathogens are fungi, bacteria or viruses that can infect and kill insects.· Pathogens require specific conditions (e.g. high humidity, low sunlight) to infect insectsand to multiply.· Most insect-pathogens are specific to certain insects groups, or even certain lifestages of an insect.· Commonly used insect-pathogens are Bacillus thuringiensis (Bt), and NPV virus.Nematodes· Nematodes are very little worms.· Some nematodes attack plants (e.g. rootknot nematode). Others, calledentomopathogenic nematodes, attack and kill insects.· Entomopathogenic nematodes are usually only effective against pest in the soil, orin humid conditions.Natural enemies of insect pests do not damage plantsand they are harmless to people!57 Cabbage Ecological Guide - 2000
Ecology of Insect Pests and Natural Enemies4.8 Natural enemy efficiencyA successful natural enemy should· have a high reproductive rate: so that populations of the natural enemy can rapidly increase whenhosts are available,· have good searching ability,· have host specificity,· be adapted to different environmental conditions, and· occur at the same time as its host (the pest).It is probably impossible for any one natural enemy to have all these attributes, but those with several ofthem will be more important in keeping pest populations low.Efficiency of predators, in addition, is determined by their appetite. For example, ladybeetle adults mayeat as much as 50 aphids per day. To check the appetite of predators, the following experiment is easyto do.The Predator Appetite Test…!Catch a predator, e.g. a ladybeetle or a syrphid larva, and place it carefully in a jar,together with some fresh leaves and a paper tissue to avoid condensation of water.Put a leaf with a known number of prey in the jar, e.g. 20 aphids.Take another jar and place a leaf with the same number of aphids inside, but withoutthe spider or ladybeetle. This is the control, to see how quickly a group of 20 aphids can multiply.After 2 or 3 days, count the number of aphids alive in both jars. Discuss if the predator has eaten theprey and how effective it will be in field situations.Appetite is one factor to determine effectiveness. Ladybeetles, for example, are effective predators whenpest populations are high. They are thought to be less effective at lower pest densities.In case of parasitoids, the number of adults emerging from one host (the pest insect) can be an importantfactor to determine efficiency. Many adults emerging from a pest insect can each again parasitize a newhost. This way parasitoid population builds up more rapid than when only one adult emerges from a host.Related exercises from CABI Bioscience/FAO manual:4-D.1. Predation on sucking insects in insect zoo4-D.2. Cage exclusion of natural enemies in the field4.7. Direct observations of consumption rates of predators in the field4.5. Studying predators in the field.4-A.5. Measuring the parasitism level of caterpillars4-A.6. Parasitisation on diamondback moth of cabbage4-A.7. Effect of parasitisation on feeding behavior of diamondback moth4-A.17. Life cycle and biology of the parasite Diadegma semiclausum4-A.18. Life cycle and biology of the parasite Cotesia plutellae4-A.19. Life cycle and biology of the parasite Diadromus collaris4-A.20. Life cycle and biology of the parasite Cotesia glomerata4-A.21. Preference of host stages by Diadegma semiclausum (or Cotesia plutellae)Cabbage Ecological Guide - 200058
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Why this guide?About this guideThis
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Introduction1.4 Cabbage: a bit of h
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Major Cabbage Insect PestsRelated e
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Major Natural Enemies of Cabbage In
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Disease Ecology7.1 Plant diseases a
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Disease Ecology7.3 How diseases spr
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Disease EcologyThe disease triangle
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Disease Ecologygrowth malformations
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Disease Ecology7.8 Control or manag
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Disease Ecologycontaminated seeds :
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Disease EcologyTrichoderma species
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Major Diseases of Cabbage8MAJORDISE
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Major Diseases of CabbageRole of en
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Major Diseases of CabbageOnce there
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Major Diseases of Cabbage· Practic
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Major Diseases of Cabbage¤Points t
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Major Diseases of Cabbagespores wit
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Major Diseases of Cabbage¤Points t
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Major Diseases of Cabbagebut does n
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Major Diseases of Cabbage8.7 Downy
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Major Diseases of Cabbage8.8 Black
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Major Diseases of CabbageNitrogen (
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Weed Management9WEEDMANAGEMENTSUMMA
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Weed ManagementBroadleaf weeds or g
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Weed Managementcompost or it may be
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Weed Management· Check details of
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Weed ManagementTherefore, to date,
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Rodent ManagementRats are a common
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Rodent Management10.4 Rat managemen
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Rodent Management10.4.4 Biological
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Key to Some Common Cabbage Insect P
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Literature and Internet Reference L
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PESTS & DISEASES COMMON TO CABBAGEP
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Plate 3Fig. 13 : Advanced symptoms
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deficiency symptoms ---------------
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chemical --------------------------
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