Pests reduce the yield of plants in various ways. They can have a direct effect by damaging the leaves of the plant. Aphids feed by inserting their mouthparts into plant cells, this often results in leaves curling up and becoming distorted. Considering the leaves of a plant are the places where the majority of the photosynthesis takes place, it follows that a plant with stunted leaves will not photosynthesise effectively. As a result there will be smaller amounts of sugars available to be transported to other parts of the plant such as the fruits, seeds and roots.
There are already a significant number of successful biological control methods and many other organisms are being investigated in order to see if they are suitable for using in the control of pests. The advantages of the biological control method of pest management are -
- Using organisms would be safer for the environment, as opposed to chemicals.
- There is minimal threat to non-target animals.
- Once a biological control organism is introduced, it does not have to be re-introduced. Chemical pesticides must be used repeatedly, therefore more expenses and time consumed.
- It is relatively inexpensive.
- It is significantly specific and only affects the pest.
- Pests do not become resistant to organisms used for biological control.
Despite the advantages, there are also numerous disadvantages of the biological control method of pest management, which are -
- Potential risk to non-target animals.
- An effective biological control programme keeps numbers of the pest at a low level, however it rarely exterminates the pest completely.
- Frequently there is some time between introducing the control organism and a substantial reduction in numbers of the pest. Chemical pesticides act much more quickly.
A very effective control programme would use a variety of methods. We refer to this approach as integrated pest management. It often involves making use of natural parasites and predators or biological and supporting this with the infrequent use of pesticides.
The Process
The majority of animals and plants are not native to the area in which they are pests. In their new environment there are often no predators or parasites to keep their numbers in check. Biologists search the area from the which the pest originally came for suitable predators and parasites to use in a biological control programe.
Trials are carried out to ensure that the control organism - will only attack the pest, does not carry diseases that may be spread to native animals or plants, can establish itself and maintain it's numbers in it's new environment. Great care must be taken to prevent the control organisms from escaping before the trials are complete.
The control organisms are bred or cultured in large numbers, they are then released. Scientists later collect the relevant information to find out if the programme has been a success.
References
A New Introduction To Biology – Bill Indge et al, Hodder & Stoughton
