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Report 3 of 3: Cottoning
On - India
India produces 2.5 million tons of cotton each year and this crop sustains the livelihoods of over 17 million people, most of whom are poor farmers with less than two hectares of land. For many, cotton is the only source of income. Unfortunately, cotton is attacked by pests, especially the cotton bollworm caterpillar which also eats food crops. Over recent years, the cost of controlling the pests by spraying with chemical insecticides has increased so that it can now amount to up to 40% of the costs of production. Due to the over-use of pesticides, the cotton bollworm has become increasingly resistant to the chemicals available and farmers have resorted to ever more toxic sprays in an attempt to protect their crops but their effectiveness has continued to decline. This has led many farmers deeper into debt to the pesticide suppliers. Many have gone bankrupt because, when the crop fails, they are unable to pay and some have even been driven to suicide.
Cotton bollworm caterpillar
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Integrated Pest Management
A group of scientists from the Natural Resources Institute (NRI) in the UK, the Tamil Nadu Agricultural University (TNAU) and the Thailand Department of Agriculture worked with the farmers to develop and test an Integrated Pest Management (IPM) system for controlling the pests. As part of the system, the pests’ natural predators were encouraged and laboratory tests were carried out to find out when the bollworm was most easily killed by insecticides so that spraying could be restricted to use only when absolutely necessary. The use of natural pest control using viral biopesticides was also introduced.
Biopesticides
In order to explain how these are made and work, it is necessary to look into some technicalities. The subject is extremely complex and the successful application of scientific research in this area depends on a very deep understanding of the part of the scientists. Fortunately, however, the effects are easier to understand.
The bollworm, like all other living things, is susceptible to attack by viruses and the natural biopesticide used in this project makes use of this fact. One particular virus attacks only the bollworm and a few of its close relatives so it can be used to kill the pest without doing damage to other insects, animals or humans. It is, therefore, extremely safe and can be used with other parts of the IPM package.
The particular groups of viruses of interest for use in insect control are rod-shaped and so are called baculoviruses (the old Greek word baculo means "rod") and about 30 different commercial products based on these are registered as insecticides. The group used in this case is called nuclear polyhedrosis viruses (NPV) and the particular virus (because it only attacks the bollworm – Helicoverpa armigera) is known as the Helicoverpa armigera NPV - (HaNPV)
Viruses are extremely small and can not normally be seen with an ordinary microscope so they are difficult to identify without the use of sophisticated equipment such as the electron microscope. However, one of the very useful features of HaNPV is that, at one stage of its life-cycle, the individual virus particles collect together in bundles of about 30, protected by a kind of crystalline skin, so that they can be seen and identified under an ordinary microscope. It is also at this stage that the virus is highly infectious to the insect but it is also very stable and it can remain infectious in this form for many years.
In order for the virus to attack, the clusters, called occlusion bodies (OBs) must be eaten by the bollworm caterpillar so must be put onto the cotton plant. Once inside the insect, the crystalline skin dissolves and the virus begins to multiply and infect the whole of the caterpillar’s body. Over a period of days more of the OB form is produced and some are left by the caterpillar on the cotton plant while it is feeding. The infection eventually kills the caterpillar but by this time more than 1,000 million OBs will have been produced in each insect. It is this astonishing rate of production of the virus which makes it attractive to use as a biopesticide.
In order to make a supply of pesticide, dead insects are collected and ground up. This releases many millions of virus OBs which can be used to make up a spray for use on the cotton plants. Even if the caterpillars filled with OBs are eaten by predators such as birds, the OBs will pass through the birds without harming them but will still remain infectious to the bollworm, so the birds help to spread the pest control over wider areas.
Effects of the IPM programme
The programme of insect control, which was supported by the Crop Protection Programme of the UK government’s Department For International Development, has made it possible for farmers themselves to make use of NPV pesticides by developing a simple way of mass-producing the virus. A manual on the laboratory methods for the production of the virus has been produced and training courses have been held in India to enable 15 commercial producers to make biopesticide products based on NPVs.
The practical results of the work in the field have been spectacular. In Tamil Nadu itself, the use of chemical insecticides has fallen by 46% while the cotton yield has increased by 17%. The initial results provoked great interest throughout India and the work has been taken up by the Indian Ministry of Agriculture which is funding the promotion of IPM in 20 major cotton growing districts.
Where the IPM programme has been taken up in Maharashtra, the use of chemicals has fallen by 95% but the yield of cotton has increased by 70%. The reduction of production costs resulting from the IPM programme package, combined with the increase in yields from the cotton crop, greatly improved the income of the farmers involved in the project, with profits increasing by up to five times.
As well bringing financial benefits, the use of IPM also provides a great reduction – around 85% - in the health hazards associated with the excessive use of toxic chemical insecticides.
For further information on this work can be obtained from:
Programme Manager
Crop Protection Programme
Natural Resources International Ltd
P O Box 258
Chatham
Kent
ME4 4PU
United Kingdom
Intermediate Technology would like to thank Mr D Russell of NRI who supplied the background information from which this brief was prepared.
This document is an output from a project funded by the UK Department For International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.
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