Biological Control Agents

Section 1 of 6Biological pest control

What it is

• What it is Biological control uses living organisms to keep a pest population low.
• The agents are predators, parasites or pathogens.

Why farmers use it

• Why farmers use it It reduces dependence on chemical pesticides, which can pollute the environment and build up in food chains.

Parasitic wasps

• Parasitic wasps Some wasps lay eggs inside a pest insect and the pest dies when the eggs hatch.
• This method helped save cassava crops from the cassava mealybug in South-East Asia.
  • Wasps are often effective because their life cycles are highly specific.

Pathogens

• Pathogens A fungus that infects the larvae of the alfalfa weevil can control it where the fungus can grow.

Section 2 of 6Invasive species

Invasive (alien) species

Definition

• Definition A species introduced to a region where it does not naturally live.
• Introductions can be deliberate, such as pets and garden plants, or accidental, such as organisms carried on ship hulls.

Cane toad

• Cane toad Introduced to Australia in the 1930s for pest control.
  • It is toxic, so it poisons native predators, and it has few predators of its own, so numbers exploded.

Asian ladybird

• Asian ladybird Introduced to Europe in the 1990s to control aphids.
  • It is more aggressive and preys on native ladybirds.

Rhododendron ponticum

• Rhododendron ponticum Brought to the UK as a garden plant in the 1700s.
  • It grows fast, outcompetes native plants for light and space, and its leaf litter is toxic to many species.

Section 3 of 6Why research comes first

1Identify a candidate agent

• Identify a candidate agent Scientists propose an organism that attacks the pest.

2Run research trials

• Run research trials They test its effect on non-target native species, not only the pest.

3Plan for problems

• Plan for problems They work out how the agent itself could be controlled if harm appears.

4Release only if safe

• Release only if safe Proper trials could have prevented the cane toad and Asian ladybird problems.

Section 4 of 6Advantages and disadvantages

Aspect	Biological control	Chemical pesticides
Pollution	Little or no chemical pollution	Can pollute soil and water and harm other organisms
Specificity	Can target one pest, but may attack native species if untested	Often kill harmless insects as well
Long-term effect	Agent may persist and keep pest numbers low	Must be reapplied; pests can become resistant
Risk	May become invasive itself	Toxins can pass along food chains

Section 5 of 6Key terms

Term	Meaning
Biological control agent	A living organism used to limit the numbers of a pest.
Pest	An organism that harms crops, livestock or people.
Parasite	An organism that lives on or in another organism and harms it.
Pathogen	A microorganism that causes disease.
Invasive species	A species that has been introduced to an area and harms the native ecosystem.
Native species	A species that naturally lives in an area.

Section 6 of 6Exam technique

1

Saying biological control has no risks — an introduced control agent can itself become invasive.

2

Confusing predators, parasites and pathogens — predators eat the pest, parasites live in or on it, pathogens infect it with disease.

3

Saying the cane toad was introduced by accident — it was released deliberately as a pest controller.

4

Writing that invasive species always cause harm because they are 'bigger' — the harm comes from competition, predation or toxicity and the lack of natural predators.

5

Giving no reason when asked why trials are needed — refer to effects on non-target native species.