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Biological control (or biocontrol) is the practice of using one species to control the population of another.

In Silent Spring, Rachel Carson advocates biological control as a superior method of controlling pests than pesticides in that there are fewer environmental side effects. She notes that some biological controls have achieved “brilliant success” (page 178, 2002 Edition). Is this always so?

Four main types of biological control organisms can be used against pests:

  • Predators include some beetles (such as ladybugs) and true bugs, wasps and spiders. Larger animals may be introduced as predators of pests – for example when carnivores like wolves are re-introduced to control herbivorous mammals like deer or rabbits.
  • Parasitoids are mostly wasps or flies, and their larvae kill the host pest by eating it alive.
  • Pathogens include bacteria, viruses and fungi.
  • Weed eaters include beetles (including weevils), butterflies and moths, and flies.

Specialist feeders are preferred as biocontrol agents because they attack only the targeted pest. Generalist feeders may attack other non-pest species.

Biological control is an area of increasing interest. There have been some great successes—but also some disasters. An introduced species can become a worse pest than the target pest. When successful however, biological control can be self-sustaining, low cost, and can have minimal side effects.