The synthesis for integrated pest control has to be done in the following stages: 1. Pest-Wise Integrated Schedule. 2. Crop-Wise Integrated Schedule. 3. Region-Wise Integrated Schedule. 4. Large-Scale Campaigns.
Stage # 1. Pest-Wise Integrated Schedule:
The general attitude in the past has been to select the most suitable of the control measures for each pest species. To this end, there has been quite a good deal of comparison of the different methods of control. The attitude of thinking entomologists is to work out the integration of as many of these methods as necessary for the effective control of any one or a group of pest species of a crop. Such a synthesis is often quite rational. A good illustration is the control of internal feeders like the stalk borers of maize and sorghum.
The importance of these pests is increasing every day with the introduction of hybrids and other improved varieties. The methods of control of such internal feeders are far from satisfactory. Once the larvae enter the plant tissue, they get beyond the reach of contact insecticides and stomach poisons, and often the insecticides used, instead of killing the pests, continue to kill their parasites which otherwise would have destroyed a proportion of the larvae inside the stems.
More than 30 species of parasites have been recorded from the different stages of the stalk borer of maize and sorghum, and a dozen of them have been found to attack the immature stages of this pest in different parts of India. Some of them are reported to be effective in reducing the populations of the borer where climate and other conditions are favourable. The biology and habits of the important larval parasites have been studied in the laboratory, and techniques for mass breeding have been developed for a few, e.g., Glyptomorpha deesae and Trichogramma evanescens minutum.
Thus, studies have been in progress to develop a combined ecological and toxicological approach to solve this problem, and now the stage has reached when an integrated control schedule on the following lines can be confidently suggested.
The moths of these pests lay their eggs on the plant, and the larvae hatching from the eggs crawl on the plant surface for a specified period, which can be determined by actual observations on each species. Eventually the larvae enter the plant tissue and get out of the reach of ordinary insecticidal dusts and sprays.
Hence, it is suggested that spraying against these first-stage larvae should coincide with the hatching of the eggs, which can be easily determined with the help of a biometer. The spraying should be carried out just when the early hatching is expected; variation in the hatching period should determine the persistence of the insecticidal formulation and its strength, which has to be selected. The strength of the insecticides has also to be such as to ensure that the first-stage larvae will pick up the lethal dose of insecticide during the few minutes when they crawl over the plant surface.
If these specifications are taken care of, most of the newly hatched larvae will be killed before they are able to do appreciable damage. Persistence of the insecticide will last for the specific period needed to kill the first- stage larvae and no more. Parasites of the different stages of larvae and pupae can be released at a time when the stage against which they are effective reaches its peak; this can be determined with the help of the biometer.
These biological control operations against larvae and pupae can thus be integrated with chemical control directed against first-stage larvae. Lastly, the peak emergence of the moths can also be determined with the help of the biometer, and at that stage we can use the latest technique of controlling the development of the next generation with the help of the sterile male technique. Efficiency of the sterile male technique is maximum at the lowest population density of the pests.
Hence, it is quite rational to reduce the pest population from its peak at the egg stage to the lowest level at the adult stage by means of chemical and biological control, the efficiency of both of which is higher at higher population densities of the pest, and then to use the sterile male technique at the low population level of the pest at which it is most effective.
For the integrated control schedule it is necessary to take cognizance of some recent developments in entomological research.
These are:
(i) Invention of the biometer which can pointedly indicate the peak period of such phenomena as larval hatching, pupation, emergence of adults, and egg-laying,
(ii) Evaluation of a technique of bioassay for determining the relative toxicity to newly hatched larvae coming in contact with insecticide films for a minimum period (separately determined for each species) for which these larvae invariably crawl about on plant surface before boring in,
(iii) The sterile male technique, and
(iv) The latest thinking on biological control. The bioassay results indicate the insecticide and the strength to be used against particular species, and the biometer indicates exactly when chemical control, biological control, or sterile male technique should be applied.
Stage # 2. Crop-Wise Integrated Schedule:
The main study required in this integration is to find out the widest common spectrum in the control of different pests and to work out the schedule of operations, each expected to control the most important pests infesting the crop at any moment. In fact, whenever a chemical control operation is carried out it does bring about varying degrees of control of different pests present at that time, although the operation might have been only against the most important or spectacular one.
This spectrum can be enlarged and the control of different pests improved substantially if the insecticide and its time of application are chosen by taking most of the pests into consideration. Even more integration effort is needed in non-chemical control. For example, in the case of sugarcane the collection of egg-masses of both Pyrilla and top borer is suggested and removal of dead hearts is also recommended in the case of several borers.
It is best to collect the egg-masses of top borer and of Pyrilla, the shoots affected by top borer, and the dead-hearts caused by the stem and root borers in one campaign, particularly in the early season of the crop when infestation of all these pests starts.
Stage # 3. Region-Wise of Integrated Control:
Integrated pest control is a novel concept, but its theoretical simplicity masks its novelty. Even in recent years, although there has been quite a good deal of talking and writing and the idea has been catching fast, comparatively few concrete suggestions have been coming forth. The result is that some of those entrusted with the direction of practical pest control feel this concept to be Utopian.
The existence of such diametrically opposite views, the immense potentialities of this concept, the practical feasibility of evolving integrated schedules for protecting a number of crops, and the inevitability of the approach under Indian conditions, have created the urgent scientific necessity for carefully and forcefully analysing the philosophy and feasibility of integrated control.
The concept of integrated pest control was originally meant to bring about a compromise between chemical control and biological control. Before the advent of the chemical age in pest control there was no serious conflict between these two approaches. But following the discovery of DDT there was such a rapid influx of new insecticides that these poisonous chemicals began not only to bring about indiscriminate annihilation of insect fauna but also to kill the very science of entomology.
Some agricultural scientists began to feel that it was not necessary even to identify the pest trouble. Such unscientific ideas, however, did not last long and basic phenomena, such as the development of resistant strains of insects, upsetting of balance in nature, increasing hazards to human beings and livestock, began to exert their effects seriously. All the same, at the level of the individual cultivator it is still quite a difficult job to drive home a balanced view.
For any orchardist or grower of a valuable crop it is difficult to decide not to apply a pesticide in the hope that parasites and predators will keep the pest under check. In the apple orchards of Kashmir even experiments on biological control of San Jose scale became difficult because orchardists would not oblige by desisting to spray their orchards. Thus, it is desirable that entomologists should concentrate on formulating rational integrated control schedules in which both chemical and biological control find their due place, each exerting its optimum beneficial effects.
It is feasible to affect not only a compromise between chemical control and biological control but also a workable integration of all the methods of control of different pests affecting the same crop or commodity as well as those affecting different crops in a particular area. Thus, the concept of integrated control is rapidly bringing us to the threshold of reliable unified approach to our pest problems as a whole.
Recent Need for Integrated Control:
There are so many instances in the world where dependence on chemical control alone first created health hazards and upset the balance in nature, and then began to fail in controlling the pest. It is to forestall these serious limitations of chemical control that integrated pest control is now being seriously considered. Another recent consideration necessitating integrated control is that agriculture has been following a progressive trend towards narrowing the germ-plasm in the field.
Agriculture originated in the practice of monoculture in place of mixed vegetation, thereby leading to the origin of insect pests. Now these monocultures of mixed germ-plasm are being replaced with those of narrower and narrower germ-plasm in the form of pure varieties.
These are further leading to adverse effects so far as pest control is concerned. These adverse side- effects of modern agriculture can be minimized to a large extent by replacing single-approach pest control with diversified pest control, which should be properly integrated and scheduled.
Genetic-Cum-Statistical Basis for Integrated Control:
The novelty of this method lies in the basic principle on which the superior efficacy of integrated control has to depend. It is a fairly well known genetic-cum-statistical principle that in any natural population there is individual variation in almost all biological characters, and the frequency distribution of a particular character generally follows a normal curve, a majority of the individuals occupying the central region below this curve and small minorities lying at two extreme ends.
Thus, in the diagram (Fig. 13.1 B) illustrating the distribution of the individual susceptibility and resistance (IS and IR) of an insect population to an insecticide there is a small proportion of highly susceptible individuals (IS) occupying a small portion of the area on the extreme left and also a small proportion of highly resistant individuals (IR) on the extreme right, with majority of the individuals of normal susceptibility and resistance in the major portion of the middle region.
Hence, when the population is treated with the dosage (D1) of the insecticide, practically the whole population will get wiped out except the portion (IR) which, if all other conditions remain normal, will multiply in the next generation; and if this is repeated for a number of generations a resistant strain will emerge. In another diagram (Fig. 13.1 A) illustrating another distribution of individual capacity of the same insect population to escape predator attack.
There will be a few high susceptible individuals (PS) becoming prey to a very low population density of the predator occupying a small area in the extreme left of the diagram, and also a few requiring quite a high density of predator population to succumb occupying the extreme right-hand area of the diagram (PR); majority with normal susceptibility to predators will occupy the major portion of the middle area. If this insect population is exposed to a predator population density (D 2), the entire population will succumb except (PR).
It has to be appreciated that individuals belonging to PR group (Fig. 13.1 A) and those belonging to the group (IR) in diagram B are expected to be randomly distributed in Fig. 13.1 A. Hence, when the population is treated by the insecticide dose D 1 most individuals of group PR are likely to be killed, and when the population is exposed to the predator population density D 2 practically all group IR will succumb.
Thus, if the same population is exposed successively to both the treatments, i.e., chemical control and exposure to predator population, both IR and PR groups will be practically wiped out and development of a resistant strain will be considerably delayed. If the 2 insecticidal applications are replaced with 1 insecticidal application and 1 exposure to predators, the amount of insecticide used will be considerably less, with the least health hazards and upset of the balance in nature.
There are some advantages of integrated pest control schedules.
They are:
1. They fit well in the national economy, and are desirable for developed countries, these are but mentable for developing countries. Our pest control activities at present are mainly based on the applications of chemical pesticides, large quantities of which have to be imported. Our plans for plant protection are also based mainly on pesticides. The expenditure runs into crores of rupees even when only 1 or 2 pesticide applications are envisaged.
On the other hand, experiments on high yielding varieties show that many more pesticide applications are required. This means that as the acreage under high-yielding varieties increases, it will be impossible to meet the demand for pesticides if we continue to depend wholly on them. Thus, a time has come when integrated pest control is not only advisable but also inevitable.
2. They offer more efficient and cheaper control. In integrated control schedules an effort is made to utilize various methods of control including use of pesticides, but at times and in some cases it is feasible to nip the trouble in the bud even by mechanical control, e.g., destruction of egg- masses of some pests early in the spring. This means much saving of pesticides, money and of foreign exchange.
Very often, pesticides are applied when the pest has already done considerable damage. This can be easily taken care of in an integrated schedule of which the successive steps need to be taken only if the previous steps have not been very effective.
3. They avoid upsetting the balance of nature. Chemical control has often been reported to upset the balance in nature, at times leading to the upsurge of new types of pest troubles. The seriousness of mites as pests of several crops has resulted from the use of DDT in many parts of the world. It is confidently expected that such adverse side-effects will be much less with integrated control schedules.
4. They will avoid or delay considerably the development of pesticide resistant strains of pests. Development of pest strains resistant to pesticides has been the most disconcerting experience of pest control scientists and technicians. From all that is known to date it is certain that this phenomenon is the result of killing out of the susceptible portion of pest population, leaving the resistant individuals to multiply free from any competition.
However, it is not likely that individuals resistant to one method of control are equally resistant to another method, and it is possible that those resistant to a pesticide are susceptible to a biological control agent. Hence, if biological control follows chemical control, the undesirable screening effects of the pesticide application can be nullified. In this way the more the methods of control are diversified and practised as components of a well-planned integrated schedule, the less will be the chances for the development of resistant strains of pests.
5. They will considerably minimize residue hazards of pesticides. It is obvious that in an integrated control schedule the use of pesticides will be considerably reduced. Hence, the pesticide residue hazards will be automatically minimized.
6. Pesticide industry will get a boost instead of being harmed. Despite what has been stated in the foregoing paragraphs, the pesticide industry will not lose but actually gain as a result of integrated control coming in vogue. In conclusion, therefore, it may be stated that a time has come when we should stop debating whether integrated control should be accepted or not and instead try to formulate integrated control schedules with existing knowledge. The main aim should be clearly understood as planned diversification of control methods so as to checkmate the pest, as in warfare.
Stage # 4. Large-Scale Organized Campaigns:
There are points in favour of and against co-operative farming, and it is considered to be one of the most controversial subjects under Indian conditions. All the same, for pest control co-operative endeavour is essential. The most spectacular peculiarity of insects is that they have an effective and efficient capacity for free flight. There is no other form of life which is so minute in size and yet able to undertake active flight for a long distance. Bacterial and other spores are carried about with the wind but passively and at the mercy of the wind.
Besides the development of wings the secret of this extraordinary capacity for free flight in insects is that they have developed very effective water-proofing mechanism against dangers of desiccation, which acts as a limiting factor in the evolution of smaller size in other free-living terrestrial and aerial fauna; for the smaller the size of the animal, the more the exposed surface area per unit body weight and the more the dangers of desiccation of active aerial existence.
Insects have evaded this general principle by developing special anti- desiccation mechanisms. The implication of this functional and structural superiority of insects over other forms of life is that they cannot be easily controlled unless the control operations are carried out over as large an area as possible and also as simultaneously as possible. Otherwise the good effect of control operations is diluted or nullified by the migration of insect from the surrounding untreated areas.
Hence, it is absolutely necessary that progressive farmers should try their best to carry with them their less enlightened colleagues in pest control operations. In any case, special efforts are necessary to organize large-scale pest control campaigns as depicted diagrammatically in Fig. 13.2 Such planning is very necessary in case of eradication campaigns, but it should also form the basis of large-scale control campaigns for ensuring optimum benefits.
The idea is that a suitable compromise has to be worked out between intensiveness and extensiveness of each individual campaign, depending on the nature and distribution of the pest, its mode of dispersal, crop season, etc.
The strategy depicted in Fig. 13.2 consists of selecting a spot or spots (A, B, C, etc.), at which the pest is specially serious, as centres or sub- centres of pest control operations. Thereafter, the required intensity of the operation has to be carefully decided as the first step, and its economics has to be calculated.
Then, depending on the available resources a circle of manageable dimensions should be drawn with the chosen spot as the centre, and during the first season control operation should be concentrated within that circle to bring down the pest population to the desired level (or for eradication, if this is the aim).
As a result of this intensive operation during the first year it is expected that the pest problem in the following year will be much milder within the treated circle. Hence, next year the control operation can be extended to a bigger circle around that of the first year. In this way the area under control can be increased year after year, and it can be ensured that the control achieved in the inner treated area is not nullified by migration of pests from the surrounding untreated area.
Where more than one spot has been selected to start the campaign, as shown in Fig. 13.2, the expanding concentric circles around the different spots (A, B, C, etc.) will in due course meet one another, and the areas left untreated between these circles can be taken care of in subsequent years.
Thus, a much bigger circle of the treated area will emerge. In this way the effect of the control campaign can be saved from being diluted or nullified by migration. The area has to be treated in circles instead of squares or rectangles to ensure uniform borer effect around the treated area.
These are some of the special requirements of pest control as distinct from other operations of crop husbandry. A pest control campaign is best organized by such government of other agencies as can ensure 100°C coverage of the area. This can be accomplished only with insurance against pest infestation or with what may be called Plan Health Scheme, somewhat on the lines of the Central Government Health Scheme, so that some levy can be charged and freedom from pest reasonably assured.
Otherwise, the good effect of piecemeal control is bound to be diluted or nullified, depending on the areas over which it has been carried out and on the migration propensities of the pest concerned. The idea of crop insurance is slowly catching public imagination. It is not, however, urgently and inevitably needed for pest control.