Chemical and biological control of agricultural pests

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Chemical and biological control of agricultural
pests

• 5.5

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Learning Objectives

• All students should know
• What pests and pesticides are.
• Most students should know
• The features of an efficient pesticide.
• How biological agents are used to control pests.
• Some students should know
• How integrated pest control systems are managed
  and what it involves.

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Success Criteria

• All Students
• I can match the key terms associated with its
  definition, by completing the cross word activity
  correctly.
• Most students
• I know the features of pesticides and how they
  work to control pests, this was demonstrated by
  correctly matching the explanations of these
  specific terms with the cut and stick activity.
• I can describe and explain how biological agents
  are used to control pests by correctly answering
  plenary questions.
• Some students
• I can write a detailed account on, why isnt the
  use of the cane toad in Australia a good example
  of an integrated pest control system?

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Starter Activity

• Across
• 7. can not be broken down by micro-organisms.
• Down
• large area of land that contains only one type of
  species.
• toxic chemical used to kill pests.
• toxic chemical used to kill weed.
• can be broken down into non-toxic substances by
  micro-organisms.
• the build up of toxic chemicals.
• an unwanted organism that interferes with human
  activity and reduces crop yield.

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Starter activity Answer

• Across
• 7. can not be broken down by micro-organisms.
• Down
• large area of land that contains only one type of
  species.
• toxic chemical used to kill pests.
• toxic chemical used to kill weed.
• can be broken down into non-toxic substances by
  micro-organisms.
• the build up of toxic chemicals.
• an unwanted organism that interferes with human
  activity and reduces crop yield.

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Management of Pests

• Pests are organisms that compete with humans for
  food sources and space.
• Controlling pests is important in the
  agricultural industry. If not treated properly
  pests will invade our crops, damaging human food
  sources.
• There are two main ways to manage pests
• Using pesticides (chemical control)
• Using predators or parasites (biological
  control)

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Chemical Control

• Pesticides are toxic chemicals that kill pests.
  Ideally pesticides should be

Selective only kills the species it is supposed to.
Biodegradable can be broken down into non toxic substances. It should be non toxic to other organisms
Cost effective development cost of pesticides are high and is only useful for a limited period of time as pest will become resistant to it over time. How does this happen?
Not accumulate build up of pesticide in specific parts of an organism is not ideal as it will be passed along food chains.
Non mobile stays where it is applied.
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Bioaccumulation

• Bioaccumulation can occur where the pesticide is
  not broken down.
• Pesticides tend to be fat soluble and accumulates
  in the environment and in food chains. It builds
  up in the fatty tissues and can not be excreted
  as waste product.
• This problem becomes worse as the pesticide
  progresses along the food chain. This is because
  organisms from higher trophic levels will eat
  large numbers of organisms from the lower trophic
  level.

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Example of Bioaccumulation (1)
?
?
?
Some pests not killed, still containing low
concentration pesticide
Small birds feed on many insects. Building up
higher concentrations of pesticide in their fatty
tissues. But not toxic enough to kill small bird.
Low concentration of pesticide on crop
Birds of prey eat many small birds accumulating
very high concentrations of pesticides in their
fatty tissue. These toxic levels may kill the
bird.
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Example of Bioaccumulation (2)
?
?
?
DDT in zooplankton (0.04 ppm)
DDT Insecticide in water (3 x 10-6 ppm)
DDT in large fish ( 2ppm)
DDT in fish-eating birds (25ppm )
Another example of bioaccumulation is DDT, it was
used as an insecticide to kill mosquitoes. But
insects slowly became resistant to it. High
toxicity of DDT was found in fish which was
consumed by birds. As you can see in this food
chain the fish has about 10 times more DDT than
zooplankton
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Biological control

• Predators and parasites of the pests can also be
  used to control pests. An example of this could
  be ladybirds controlling insect pests on citrus
  fruits.
• Using a biological control does not eradicate the
  parasite but controls it, so it is manageable
  and natural.
• Ideally the parasite and pests should be in
  balance with each other. Where the pest has
  little effect.

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Differences between chemical and biological
control

• Biological control

• Chemical control

• Can have some effect on other non-targeted
  organisms.

• Reapplied at intervals ? expensive

• Pests can develop genetic resistance to
  pesticides overtime.

• Very specific, chosen predator would only eat the
  pest.

• Control organism reproduces itself once it has
  been introduced therefore cheaper more cost
  effective.

• Pests does not become resistance.

• No pollution

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Differences between chemical and biological
control

• Biological control

• Chemical control

• Very specific, chosen predator would only eat the
  pest.

• Can have some effect on other non-targeted
  organisms.

• Pests does not become resistance.

• Pests can develop genetic resistance to
  pesticides overtime.

• Control organism reproduces itself once it has
  been introduced therefore cheaper more cost
  effective.

• Reapplied at intervals ? expensive

• No pollution

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Integrated pest-control systems

• These systems include both types of controlling
  methods to produce a better result for the
  management of pests.
• This type of control aims to reduce the effects
  of pest with minimal impact on the environment.
• Integrated control involves
• The introduction of an organism that is better
  suited to the local environment and is
  pest-resistance.
• Provide suitable habitats for the crops.
• Monitor crops for signs of pests regularly for
  earlier prevention.
• Remove pests when it exceeds the acceptable
  population level.
• Use biological agents if necessary
• If the situation starts to get out of control use
  pesticide as last resort.

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Cane Toad Video

• You will watch a video on the use of the cane
  toad as a method of biological control. After
  the video you will be expected to write the
  following account Why shouldnt the cane toad
  have been used as an biological control system
  in Australia?

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Pest and Productivity

• Pests often competes with crops for resources.
  These resources are often related to the rate of
  photosynthesis, mineral consumption or space.
• Can you think of any limiting factors of
  photosynthesis?
• Pests can also affect the human food source by
  consuming it themselves, directly competing with
  humans.
• Both points above shows how pests interfere with
  crops to reduce productivity.
• The overall aim of pest control is to balance the
  cost and benefits it brings. Farmers often have
  to think about how to produce cheap food to
  satisfy their costumers and make profit.

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Plenary Summary Questions

1. Pesticides are used to increase productivity.
   Explain how their use might sometimes reduce
   productivity. (3 marks)
2. State two advantages and two disadvantages of
   biological pest control. (4 marks)
3. Weeds are growing amongst wheat in a field.
   Explain how these weeds might reduce the
   productivity of a crop. (3 marks)

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Peer Assessment Answers

• Pesticides will kill most of the pests-reducing
  its population. This in turn reduces the
  population of its predators. (1 mark) However,
  with no predators controlling pests after
  pesticide was introduced, the population of pests
  starts to increase. (1 mark) This could be higher
  than the pest population before, increasing the
  effect of pests on the crop reducing
  productivity.(1 mark)
• Advantages any 2 from highly specific, targeted
  only by pest/once introduced it reproduces itself
  and does not need to be reapplied/pests do not
  become resistant. (2 marks)
• Disadvantages any 2 from effect id
  slow as there is a time lag between application
  and results/ may itself become a pest or may
  disrupt the ecological balance. (2 marks)
• 3. Weeds compete with the crop for sources
  (e.g light, water, mineral ion, space, carbon
  dioxide..) limiting the supply for crops. (1
  mark) This limits the rate of photosynthesis and
  therefore reduces productivity. (2 marks)

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Learning Objectives

• All students should know
• What pests and pesticides are.
• Most students should know
• The features of an efficient pesticide.
• How biological agents are used to control pests.
• Some students should be able to
• Know how integrated pest control systems are
  managed and what it involves.

20
Success Criteria

• All Students should know
• I can match the key terms associated with its
  definition, by completing the cross word activity
  correctly.
• Most students should know
• I know the features of pesticides and how they
  work to control pests, this was demonstrated by
  correctly matching the explanations of these
  specific terms with the cut and stick activity.
• I can describe and explain how biological agents
  are used to control pests by correctly answering
  plenary questions.
• Some students should be able to
• Write a detailed account on, why isnt the use of
  the cane toad in Australia a good example of an
  integrated pest control system?

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