“Phages (viruses that infect bacteria) can be used as vectors in the genetic engineering of bacteria, so viruses which attack plant cells should open up the possibility of doing the same in plants”(Using Viruses, Biological Science 2, Taylor, Green and Stout). This technique is still being developed. Biotechnology is engineering man-made viruses to target only certain pests. These viruses are harmless to other species, and will later self-destruct.
Chemicals can be synthesised, such as those produced by insects to warn their fellow insects of danger, used by farmers to scare them away from crops. Chemicals used by insects to attract a mate have been synthesised to attract insect pests into traps. Some chemical compounds in use are totally synthetic, but others derive from natural chemicals that are the enhanced and developed by scientists.
Fungi pathogens are controlled by the use of specific chemical fungicides, for instance, the rice blast and rice blight were both stopped by the use of a specific chemical. New compounds are being developed to stop fungi pathogens from adapting. Strobilurins are also being developed. These are based on naturally occurring fungi, and are toxic to other fungi pathogens.
Old weed killers (such as 2,4D) are still in use because they are much cheaper than newer herbicides. However, a lot more is required to be effective in the killing of plants. Old weed killers are very good at killing a wide range of different weeds. However, many wanted plants may also be killed in the process. If it is washed into rivers or lakes, pondweed and other underwater plants will be killed, removing the source of food for many fish and insects. New herbicides have a much shorter persistence and will break down in soil into harmless elements.
Chemical insecticides are strictly controlled in most countries because of harm caused to beneficial insects such as bees and beetles. Insecticides have been developed less than any other pest control because they are poisonous and some, such as DDT, are stable. This means they cannot be broken down or excreted, so are passed on to other animals that eat something containing DDT. Insecticides are sprayed onto crops. When insects eat the plant they also eat some insecticide. If other animals eat the insect it accumulates. Eventually the pesticide concentrates in larger animals, such as otters, and kills them. Large animals at the top of the food chain find it harder to recover as they have less offspring and their food source has been removed.
Most pesticides lose their effectiveness over time. Chemical pesticides do not usually kill the entire population of pest in that area. The ones that survive have resistant genes and their offspring will inherit this resistance to pesticide and so be harder to kill in future. To develop alternative pesticides is expensive and the same thing could easily happen again.
Biological pest control is generally cheaper and “some biological control measures can actually prevent economic damage to agricultural crops”(). They are usually specific and do not affect other insects or animals. There is less danger of impact on the surroundings.
However, Biological control can take, months rather than weeks to become effective. The results are not as dramatic or quick as the results of chemical pesticide use. On building sites, rail tracks and motorways you may want all plant life to be killed. In these circumstance it would be better to use a chemical that will not break down or only kill certain pests.
Generally, biological pest control is better than chemical control as it doesn’t pollute the environment or affect other plants or animals. However, there are some circumstances when it would be more sensible to use a chemical.
Bibliography
- ipmwww.ncsu.edu/biocontrol/introduction.html
- Encarta 99 Encyclopedia
- ‘Biological Science 1’, by Stout, Green and Taylor
- ‘Biological Science 2’, by Stout, Green and Taylor
- ‘Advanced Biology’, by Kent
- encarta.msn.co.uk/find/search
