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MICROBES IN HUMAN WELFARE
and harmful life forms indiscriminately, this is a holistic approach that
seeks to develop an understanding of the webs of interaction between the
myriad of organisms that constitute the field fauna and flora. The organic
farmer holds the view that the eradication of the creatures that are often
described as pests is not only possible, but also undesirable, for without
them the beneficial predatory and parasitic insects which depend upon
them as food or hosts would not be able to survive. Thus, the use of
biocontrol measures will greatly reduce our dependence on toxic chemicals
and pesticides. An important part of the biological farming approach is
to become familiar with the various life forms that inhabit the field,
predators as well as pests, and also their life cycles, patterns of feeding
and the habitats that they prefer. This will help develop appropriate means
of biocontrol.
The very familiar beetle with red and black markings – the Ladybird,
and Dragonflies are useful to get rid of aphids and mosquitoes,
respectively. An example of microbial biocontrol agents that can be
introduced in order to control butterfly caterpillars is the bacteria Bacillus
thuringiensis (often written as Bt). These are available in sachets as dried
spores which are mixed with water and sprayed onto vulnerable plants
such as brassicas and fruit trees, where these are eaten by the insect
larvae. In the gut of the larvae, the toxin is released and the larvae get
killed. The bacterial disease will kill the caterpillars, but leave other insects
unharmed. Because of the development of methods of genetic engineering
in the last decade or so, the scientists have introduced B. thuringiensis
toxin genes into plants. Such plants are resistant to attack by insect pests.
Bt-cotton is one such example, which is being cultivated in some states
of our country. You will learn more about this in chapter 12.
A biological control being developed for use in the treatment of plant
disease is the fungus Trichoderma. Trichoderma species are free-living
fungi that are very common in the root ecosystems. They are effective
biocontrol agents of several plant pathogens.
Baculoviruses are pathogens that attack insects and other arthropods.
The majority of baculoviruses used as biological control agents are in the
genus Nucleopolyhedrovirus.
These viruses are excellent candidates for
species-specific, narrow spectrum insecticidal applications. They have
been shown to have no negative impacts on plants, mammals, birds, fish
or even on non-target insects. This is especially desirable when beneficial
insects are being conserved to aid in an overall integrated pest
management (IPM) programme, or when an ecologically sensitive area is
being treated.
10.6 MICROBES AS BIOFERTILISERS
With our present day life styles environmental pollution is a major cause
of concern. The use of the chemical fertilisers to meet the ever-increasing