Is the use of pesticides an acceptable form of pest control?

A pesticide is any substance or mixture of substances intended for preventing, destroying, or repelling any pests. Pests can be insects, mice and other animals, unwanted plants (weeds), fungi, or micro-organisms like bacteria and viruses. The different types of pesticides include herbicides (weed killers), fungicides, insecticides and other chemical substances.

Pesticides use a variety of different chemical substances (such as organophosphates and organochlorines) which can be classified into the following groups: Contact pesticides where the pesticide is sprayed directly onto the crop and usually absorbed by the insect through tiny gas-exchange pores along it’s body.

They are inexpensive but often have to be reapplied.

Systematic pesticides are also sprayed directly onto the crop and absorbed by the leaves, but the pesticide then transports itself around the plant. Therefore if a sap-sucking insect such as an aphid should feed onto the crop plant, it takes in the pesticide and is poisoned.

This type of pesticides is effective because it is not necessary for the spray to come into contact with every insect. They are selective in their action. They affect only certain pests.

They are also inexpensive and also need to be reapplied often.

Residual pesticides are sprayed onto the soil or treated to the seeds before the crop is planted. This means they stay active in the soil and will kill any spores, eggs and larvae as well as weed seedlings as they germinate.

These are inexpensive too but don’t have to be reapplied, as they remain active in the soil for long periods of time. [Bill Indge et al, published in 2000, “A New Introduction to Biology”, page 211-212]

Unfortunately there are hazards to using chemical pesticides. The World Health Organization estimates that pesticides poison at least three million people each year. In some parts of South East Asia 7 to 15 % of farmers experience poisoning at least once in there lives.

In some parts of South America, agricultural workers have shown inhibition of the blood enzyme, cholinesterase, which is a ...

This is a preview of the whole essay

In some parts of South America, agricultural workers have shown inhibition of the blood enzyme, cholinesterase, which is a sign of organophosphate poisoning. These poisonings have often lead to death. (In Venezuela, there were 10,300 cases of poisoning with 576 deaths occurred between 1980 and 1990.) []

Even in parts of the UK, farmers and their families are being diagnosed with illnesses, which are associated with pesticide poisoning. Such conditions as Multiple sclerosis are occurring to many of the farmers, especially in the cases where they use sheep dipping as part of their work. [World in Action video, Organophosphates]

Pesticides can also adversely affect wildlife through changes in the food web, via direct and indirect poisoning.

In the 1960s, wildlife biologists were puzzled when the gannet population in Quebec, Canada began to shrink. The shells of the gannets' eggs were too thin to protect the embryos, therefore when the mothers tried to turn the eggs; they were too fragile and so cracked very easily killing the young inside.

When the eggs had been analysed, the scientists identify the culprit DDT, which had been bio-concentrated through higher levels of the food web. The fish in the sea had been poisoned and this passed to the gannet populations. The populations of other predatory birds such as eagles and peregrine falcons were also affected in the same way.

[]

Wildlife habitat is also affected as the birds and mammals, which depend on specific habitats, were no longer able to live in their natural environments due to the use of the herbicides in the soil they occupied. Their predators were also affected, as there are no prey left for them to feed on.[ ]

An alternative method to chemical pesticide use is using biological pesticides or Bio-pesticides. Bio-pesticides are certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals.

An example of this is using other animals to get ride of pests.

Examples of include using ladybirds to control aphids, using cactus moths to control prickly pear cactus, using the parasitic wasp Encarta to control whitefly in greenhouses, using myxomatosis to control rabbits in Australia etc.

Advantages of these would be that they are specific as they only target the pest species, the pest are unlikely to develop a resistance to the predator and once introduced, there is no need for further reintroduction.

However there are slight disadvantages, as research is needed to ensure that the control agent will control only the pest and not other closely related species and that they would survive in the environment that they are introduced into.

It is also essential that a different pest be not fit into the ecological niche left by the pest (i.e. if you get rid of one pest, which feeds on a crop to find that another pest feed on the same crop)

[Class notes from AQA exam board]

Integrated Pest Management (IPM) can be used as a compromise to using chemical pesticides, where the crops are treated as an ecosystem, and different methods are used to control the pests within it.

The principle of INP is that it is only undertaken when pest populations are at, or near, "economic thresholds" which may threaten a crop's commercial value.

IPM uses biological controls wherever possible, but it also uses other techniques if necessary including limited, specific applications of a chemical pesticide. The integrated approach actually tolerates some pests, so long as the damage they cause remains minor. In fact, small pest populations are welcome, since they ensure that the pest's natural enemies will also survive in the system.

IPM can allow for the growth of the right crop for the conditions, e.g. soil type, climate.

It allows crops to be grown with natural resistance to pest in the area.

Using IPM, farmers can depend on a method called "crop rotation" to control pests. A variety of crops are planted and then rotated to different fields each year. Pests that attack one variety will die off when that variety is replaced by a different crop the following year. In many cases, removing their preferred food and shelter can control pest populations.

Overall it can said that pesticides prevent crops from being destroyed by pests, however pesticides can also cause serious illness and often death to both humans and animals alike. Using bio-pesticides as well Integrated Pest Management, can limit the amount of pesticide use by combing both the use of chemicals and nature together.

Bibliography