You can deploy other organisms to reduce pest
numbers which can act as predators or parasites.
e.g. cane toads were introduced into
Australia to eat beetles causing crop damage.
These biological methods can be
more sustainable than chemical pesticides, so less harmful to the
They do not involve toxic chemicals
that can poison harmless organisms and accumulate in food
chains and passed on from one trophic level to the next.
This means less pollution, less risk
to people and other wildlife!
BUT, there is often a 'but' e.g. the cane
toads are now a 'pest' because they poison native animals that
Quote from Wikipedia: "The long-term
effects of toads on the Australian environment are difficult to
determine, however some effects include the depletion of native
species that die eating cane toads; the poisoning of pets and
humans; depletion of native fauna preyed on by cane toads; and
reduced prey populations for native insectivores." - not good!!!
Introducing one organism to control
another can lead to unintended consequences.
You can control aphids (greenfly and black
fly) by employing a predatory insect - can be very effective in the
confines of a large greenhouse.
e.g. ladybirds will eat greenfly,
Parasitic wasps can be introduced to
control aphid populations that feed on fruit crops - the wasps
lay their eggs inside the aphids, which die when the larval
wasps hatch out.
The wasp parasites act as a vector' when
introduced to control pests e.g. another example is flies laying their eggs on
slugs to kill them.
Bacteria can be used to deliberately infect
caterpillars with diseases.
BUT, there are always risks in adding
another organism to an existing ecosystem, you can never be sure
of 'unintended' long term effects!
Some of these biological methods of pest
control are used in large scale greenhouses and hydroponics units -
these are good methods of 'factory farming' plants - see sections
(h) and (i).