Biological Control Agents (WJEC GCSE Biology: Combined Science)

Biological pest control

• Biological control agents are living organisms that are used to limit populations of pest species, keeping their numbers to a minimum
• Biological control organisms include:
  • Predators
  • Parasites
  • Pathogens
• Biological control allows farmers to reduce reliance on chemical pesticides, which can cause problems with pollution and toxicity in food chains
• Examples of biological pest control include:
  • Parasitic wasps may lay their eggs inside the bodies of pest species, which then die when the wasp eggs hatch
    • This method was used to save cassava crops from the cassava mealybug pest in South-East Asia
  • A fungal pathogen can be used to infect the larvae of the alfalfa weevil, controlling populations of the pest in environments where the fungus grows

Katja Schulz, CC BY 2.0, via Wikimedia Commons

Parasitic wasps are often effective biological control agents due to their highly specific life cycles

Invasive species

• Invasive species, also known as alien species, are species introduced to regions where they do not naturally occur
  • Humans may introduce a species on purpose, e.g. as a pet or a garden plant
  • Organisms may travel using human transport, e.g. attached to the hull of a ship, resulting in accidental introductions
• These species can cause problems for native ecosystems in the areas to which they are introduced, e.g.
  • Cane toads were introduced to Australia in the 1930s as a form of biological pest control, causing huge problems for native wildlife
    • The cane toad is toxic to consumers, meaning that it poisons native Australian predators
    • The lack of suitable predators means that cane toad populations have exploded
  • The Asian ladybird was introduced to Europe in the 1990s in an attempt to control aphid populations, but research shows that the species is damaging European ladybird populations
    • The Asian species is more aggressive and will predate on the native species
  • Rhododendron ponticum was introduced to the UK as a garden plant in the 1700s, but has become invasive in native woodlands
    • It grows fast, outcompeting native plant species for light and space
    • Its leaves, when dropped, produce leaf litter that is toxic to many other species

Bernard Dupont, CC BY-SA 2.0, via Wikimedia Commons	Ryan Somma, CC BY-SA 2.0, via Wikimedia Commons

Invasive species, such as cane toads (left) and Rhododendron ponticum (right) can disrupt natural ecosystems; this may be due a lack of effective natural predators or their ability to outcompete native species

Biological control research

• In order to use effective biological control agents without causing ecological harm, it is essential that new potential agents are properly researched before they are released into non-native environments
  • Proper research may have prevented the problems caused by the introduction of cane toads and Asian ladybirds
• Scientists around the world need to carry out research trials to assess:
  • The effect of potential control agents on non-target native species
  • The best way to control the agent itself should any non-target effects arise