The unceasing struggle between man and his insect enemies started even before the dawn of civilization. Inspite by the numerous advances made by man in evolving newer and deadlier weapons to fight the war against insects, he has not succeeded in eradicating even one of the thousands of serious pests which damages his food and other agricultural products, destroys his possessions and even attack himself and injure his domestic animals.
There generally exists an uneasy truce between the insects pests and man , and this is termed as 'balance in nature'. This balance is the result of two opposing phenomena, the 'biotic potential',i.e.,the tremendous capacity of insects to reproduce and multiply and the environment resistance which keeps their numbers under check. The environment resistance results in the death of adults before oviposition, in the mortality of eggs, larvae or pupae of the insects because of desiccation, starvation, parasites, predators, diseases and other adverse environmental conditions. Even any slight slakening of any of the processes of 'environment resistance' results in a population explosion of an insect species and the consequent epidemic.
The change in 'environment resistance' may take place owing to a number of causes, either natural of operated by different agencies. Man is perhaps the single most important agent, who has, from time to time, disturbed the 'balance of nature' and this has caused numerous pest problems and pest epidemics. The nature too, plays an important role in causing pest epidemics. Favourable conditions which reduce the natural mortality and bring down the rapid development of the insect coupled with the conditions unfavourable to the natural enemies of that insect, often result in the rapid increase of its population leading to a sudden pest out-break.
PRINCIPLES OF INSECT-PEST CONTROL
Once it is established that an insect is causing economic losses, it becomes necessary to control it.
The first princlple undelying the control of an insect is its correct identification. When it is correctly identified, we can refer to the available information on the biology and the habits of the insect and determine its most vulnerable stage, the appropriate time and the most suitable method or methods to control it.
The knowledge and understanding of the ecological factors, both biotic and abiotic, affecting the population of the insect pest is necessary for planning the proper strategy for controlling it. A lot of attention is paid to this aspect now and elaborate procedures and 'models' have been evolved to pinpoint the 'key factors', dominantly affecting the development and multiplication of a particular pest.
The choice of the proper method or methods of control becomes easier, when the above mentioned information becomes available in respect of a particular pest. Some of the important methods for control of insect pests are discussed below.
- Physical and Mechanical control
This is one of the oldest methods, and has been in use since time immemorial. It includes measures like, collection of egg masses and other inactive stages, the removal of infested parts or whole plants, the beating of drums or tins or trenching. This method can prove to be effective during the initial stage of the pest incidence and when practised as a concerted effort by a large number of farmers in a particular area.
This is a preventive method which is inexpensive and may prove more efffective and efficient, if employed after acquiring a through knowledge of the life history and habits of a pest. Deep ploughing after harvesting the crop ( to expose the hiding and resting insects), the removing and destroying of the suitable and other trash, adjusting the time of sowing (toavoid the peak incidence period), clean cultivation, the removal of alternative wild hosts, catch crops & suitable rotations are some of the important measures included under this method of control.
Host plant resistance has generally been considered one of the components of cultural method, but because of its importance, it desrves an independent status as a major method of protecting crops against insect damage. The method involves the utilisation of the inherent property of certain strains or varities of crops, of being less infected or less dameged than other strains or varities of same crop. Enormous economic benefits have been achieved by using this method in the case of crops, e.g. wheat,maize, cotton and alfalfa.
Very little attention has so far been paid in India to the exploitation of this method. However under the various co-ordinated projects on the improvemnet of any crop, special attention is being given to the evolvement of varities resistant to major insect pests. It is realised that the success of this method requires the close co-operation of entomologists, geneticists and plant-breeders.
Practically every crops pest has its natural enemies in the form of parasites, predators and disese causing organisms. The biological control involves a large scale multiplication of and liberation of such agents, or creating conditions under which the naturally occuring agents can act effectively. This type of control cannot be undertaken by individual farmers and has necessarilt to be carried out by specialised agencies.
Some very outstanding successes have been achieved by using this method, but the method suffered a set-back owing to the large-scale and indiscriminate use of insecticides. The approach at present is to evolve methods by which the biological and chemical methods can be intergrated, so that the harmful effects of insecticides do not interfere with the activities of the natural enemies.
- Legislative or regulatory method
Legislative or regulatory method is a method mainly employed to prevent the introduction of pests from other countries or to prevent the spread of a pest from one area to another. The method is operated through specific regulations known as palnt-quarantine laws. In India some states have special pest acts, by which it becomes obligatory on the part of the cultivators and govermental authorities to take appropriate steps to control a particular pest when it appears in an epidemic form.
After the discovery of the insectisides properties of DDT in 1939 by Paul Muller, the chemical control of insects has become most popular. As a matter of fact, the method has become so popular that most of the cultivators and extension workers speak only about insecticides, whenever the question of insect control is raised. The main reason for its popularity is the spectacular and immediate results obtained by the ude of such chemicals.
Hundereds of insecticides are noe available to control diffrent insect pests. These are mainly used as dusts, sprays or granules on the crops; dust and granules can also be incorporated into the soil for the control of soil inhabiting insects. In recent years, the soil application of some of the systemic insecticides has proved to be effective in controlling insect attacking crops in the early stages of their growth.
Some of the serious limitations of the insecticides have been highlighted in recent years. Out of these, the problems of insecticides residues on crops and other products used as food and fodder and on pollution of environment have been agitating the minds of people in developed and developing countries of the world. This realisation has resulted in certain extremist quarters demanding the banning the use of the most of the insecticides. However the sensible approach suggested and generally accepted is for a judicious and restricted use of insecticides. It is strongly felt that in the near future, there is no possibility of replacing the chemical method of controlling insects entirely by any other method.
SOME OTHER METHODS OF INSECT CONTROL
In addition to the major methods of controlling insects described above, there are number of other methods, which have either been employed successfully for controlling certain specific pests, or are still in the experimental and developmental stages. Increased attention is being paid now to the incorporation of such methods in the programmes of insect control. Some of these methods are : the use of attractants, repellants and anti-feeding compounds, radiations for sterilization (the well known example of eradicating the screw-worm by using sterile-male technique), chemosterilants, juvenile and sex hormones. These methods can in future replace or supplement the use of insecticides.
THE SELECTION OF PROPER METHODS FOR CONTROLLING DIFFERENT PESTS
The guiding principles for selecting an appropriate method or methods of control should be that the method chosen must be economical, free from creating any other problem, immediately or in future , it should not harm the natural enemies of the pest and should be easy to operate and be readily available to an ordinary cultivator.
The choice of the proper method (or methods) of control becomes easier when the biology and the habits of the pests are known and its most vulnerable stage has been determined. However so far the general tendency among those who are responsible for carrying out the control operations is to employ an easy method, giving quick results and disregarding other unfavourable consequences which may follow the completion of the operations.
Keeping in view the guiding princlples in the selection of pest-control methods, it is generally realized that any single approach to the problem of insect control is not feasible. Each method has its own advantages as well as its disadvantages and also has limitations under a particular set of conditions. The current thinking all over the world is to suitably synthesize the use of as many methods as possible to control the insect pests effectively, economically and without any adverse after-effect. This approach is now popurlarly known as 'Integrated Pest Control'.
Despite a number of serious limitations from which insecticides suffer, it is felt that the use of these chemicals in the control of insect pests will continue for a long time to come and in the strategy for 'Integrated Pest Control', this method will occupy an important place as a curative methods for reducing losses because to pests.
However, the emphasis is to be laid on the judicious and proper use of insecticides, so that this method may not impair the efficacy of other methods and create other problems. Keeping this point in view, some more information on insecticides and their proper use is given in the following pages.
