Pest Control

Chemical and biological control of pests

4.5

Learning Objectives All students should know:• The terms pest and pesticide• The features of an efficient pesticide• The advantages and disadvantages of chemical control• The advantages and disadvantages of biological control

• The idea of integrated pest control systems

Starter

Across 7. can not be broken down by

micro-organisms. Down 1. large area of land that contains

only one type of species. 2. toxic chemical used to kill pests. 3. toxic chemical used to kill weed. 4. can be broken down into non-

toxic substances by micro-organisms.

5. the build up of toxic chemicals. 6. an unwanted organism that

interferes with human activity and reduces crop yield.

Starter activity: Answer Across 7. can not be broken down by

micro-organisms. Down 1. large area of land that contains

only one type of species. 2. toxic chemical used to kill

pests. 3. toxic chemical used to kill

weed. 4. can be broken down into non-

toxic substances by micro-organisms.

5. the build up of toxic chemicals. 6. an unwanted organism that

interferes with human activity and reduces crop yield.

Management of Pests

Pests are organisms that compete with humans for food and soil space or are potentially hazardous to health

There are three main ways to manage pests:1.Using pesticides (chemical control)2.Using predators, parasites or pathogens (biological control)3.Integrated Pest Management

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.

Advantages of Chemical Control

•Rapid eradication of pests – little delay•Low skill level needed to apply them•All pests can be removed

Disadvantages of Chemical Control•Toxicity to humans or other non-target animals•Broad spectrum – non-target species also affected, pollinators, food chain disruption•Pest resistance – selected for•Pest replacement •Pest resurgence – seen when using broad spectrum pesticides – eradicates predator of pest and the pest, the pest may emerge without predators •Bioaccumulation – may accumulate in food chains

Bioaccumulation • Bioaccumulation can occur

if the pesticide does not quickly biodegrade

• Pesticides tend to be fat soluble and will accumulates in food chains.

• This problem becomes worse as the pesticide progresses along the food chain.

• May also accumulate in soils and affect decomposers

Example of Bioaccumulation (2)

→ → →

DDT Insecticide DDT Insecticide in water in water

(3 x 10(3 x 10-6-6 ppm)

DDT in zooplankton (0.04 ppm)

DDT in large fish( 2ppm)

DDT in fish-eating birds

(25ppm )

An 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

Biological control

• Predators, pathogens and parasites of a pest can be used to control pests. An example of this could be ladybirds controlling whitefly on citrus fruit.

• 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 present at a low level and in balance with each other. The pest should therefore have little affect.

Biological Control

Advantages•Does not harm non-target organisms, very specific•No toxic chemicals used (no residues in soils, water)•No bioaccumulation of chemicals in food chains•No resistance is developed

Disadvantages•Low level of crop damage has to be tolerated as pest has to maintain the predator•Development and research of appropriate control agents is expensive and lengthy

Differences between chemical and biological control

Biological control

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

Chemical control

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

• Pests can develop genetic resistance to pesticides overtime

• Reapplied at intervals expensive

• Pests does not become resistance.

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

• No residues, no pollution

Integrated pest-control systemsIntegrated pest control involves:1. The introduction of an organism

that is better suited to the local environment and is pest-resistance.

2. Provide suitable habitats for the crops.

3. Monitor crops for signs of pests regularly for earlier prevention.

4. Remove pests when it exceeds the acceptable population level.

5. Use biological agents if necessary 6. If the situation starts to get out of

control use pesticide as last resort.