Human Impact on the Environment

A pest is any organism (insect, weed, fungus) that damages crops, livestock or people. The traditional way to manage pests is to spray chemical pesticides on them, but this has several drawbacks:

• Pesticides kill non-target species (bees, ladybirds, songbirds) as well as the pests
• Pests evolve resistance (see topic 14), making the pesticide useless over time
• Pesticides can biomagnify up food chains (see topic 15)
• Chemical pesticides contaminate soil, water and the food we eat

What biological control is

Biological control is the use of a living organism to control a pest, instead of a chemical. The control organism is typically a natural predator or parasite of the pest:

• A predator that eats the pest
• A parasite or parasitoid that lives on or inside the pest, weakening or killing it
• A disease-causing microbe that infects the pest

Advantages of biological control

• No chemical pollution of soil, water or food
• Targets only the pest species if the control organism is well-chosen
• Self-sustaining once established; the predator population maintains itself
• No resistance develops in the same way as with chemicals
• Cheaper in the long run than repeated chemical sprays

Disadvantages and risks

• The control organism can become an invasive species if it has no natural predators in its new habitat
• It can attack non-target species, sometimes more so than the pest it was meant to control
• The cane toad in Australia is a famous example: introduced to control beetles, the toads ignored the beetles, multiplied uncontrollably, and now devastate native wildlife by being poisonous to anything that tries to eat them
• It can take a long time to work, so cannot deal with sudden pest outbreaks
• It does not eliminate the pest entirely; it just keeps the population low

Integrated pest management (IPM)

Modern farming usually combines several approaches in integrated pest management:

• Biological control as the foundation
• Targeted pesticide use only when pest numbers are very high
• Crop rotation to break pest life cycles
• Pest-resistant crop varieties (sometimes from selective breeding or genetic modification)
• Physical barriers (netting, traps)

Integrated pest management uses far less chemical pesticide than traditional farming, with similar or higher yields.