AGRICULTURAL ENTOMOLOGY AND PEST CONTROL
S. PRADHAN Head of the Division of Entomology Indian Agricultural Research Institute New Delhi
ICAR
Published by
Directorate of Knowledge Management in Agriculture
Indian Council of Agricultural Research New Delhi
First Published First Reprint Second Reprint Third Reprint
Project Director (DKMA)
Incharge (English Editorial Unit)
Chief Production Officer Officer (Production)
Technical
May 1983 May 1991 June 2002 January 2013
Dr Rameshwar Singh Dr R P Sharma Dr V K Bharti Kul Bhushan Gupta
All rights reserved Š 2013, Indian Council of Agricultural Research, New Delhi
ISBN : 978-81-7164-120-8
Price : Rs 150
Published by Dr Rameshwar Singh, Project Director, Directorate of Knowledge Management in Agriculture, Indian Council of Agricultural Research, Krishi Anusandhan Bhavan-I, Pusa, New Delhi 110 012 and printed'at M/s Chandu Press, D-97, Shakarpur,
Delhi 110 092.
CONTENTS Foreword
iii
About the Author
iv
1.
Place of Entomology in Relation to Man
1
2.
Dominance of Insects
8
3.
Insects Useful to Man
18
4.
Origin of Insect Pests
40
5.
Estimation of Insect Population
52
6.
Assessment of Losses due to Insect Pests
75
7.
Insects’ Adaptations to Arid Conditions
105
8.
Effect of Temperature on the Dynamics of Insect Development
123
Principles of Insect Control
177
10.
Pesticide Hazards
198
11.
Revolution of Pest Control
212
12.
Importance of Protection Research in Tropics
223
13.
Integrated Pest Control
239
Epilogue
260
Index
261
9.
CHAPTER 1
PLACE OF ENTOMOLOGY IN RELATION TO MAN
THE word insect has its root in the Latin word insecare (to cut into) and is equated with ‘insectum’. Entomology, the science of insects, has its origin in the Greek word temno (to cut). The Sanskrit word keet may have a similar sense and root. Thus, the most prominent physical cha¬ racteristic of insects which seems to have impressed the early observers who coined these names, is the division of the insect body into 3 promi¬ nent regions, namely, head, thorax, and abdomen; this single feature has had the most spectacular impact on the etymology of entomology. The second important character of an insect is its 3 pairs of legs; this is the basis of the term Hexapoda, meaning 6-legged, coined by Latreile in 1825 for the zoological class Insecta (Fig. 1.1). The corresponding Sanskrit
ANTENNA
HEAD
FORELEG THORAX
m
OCELLI
EYE
t
2
FORE WING
3
MIDDLE LEG
II
2
L~£5 ABDOMEN
HIND WING
6
7
HIND LEG
8 9 10
CERCUS
Fig. 1.1 A typical representative of class Insecta.
2
AGRICULTURAL ENTOMOLOGY AND PEST CONTROL
term Schatpada, also meaning 6-legged, was there in Amarkosh as early as the first century A.D. when that dictionary was compiled. The third character, which almost completes the definition of this class of animals, is the chitinous body wall, which also serves as skeleton and is called exoskeleton or outer skeleton; actually it is a characteristic of the larger group, the phylum Arthropoda, to which insects also belong. Thus, an insect may be defined as an animal which at some stage of its develop¬ ment possesses the combination of these 3 major characters, (i) chitinous exoskeleton, (ii) 6 legs, and (iii) body prominently divided into head, thorax and abdomen. In other words, insects are arthropods having a combination of the last 2 characters. In zoological classification insects constitute just one of 5 major classes of the phylum Arthropoda, which in turn is just 1 of 15 major and several minor phyla of the animal kingdom. From the economic point of view there are several groups which are important enough to have led to the development of different branches of study, such as Ornithology (birds), Ichthyology (fishes), Helminthology (worms), as well as economic departments such as those of poultry, fisheries, dairying. There is, how¬ ever, hardly any other class of animals or plants which has such vast potentialities, both for good and for bad, and such remarkable degree of even purely academic interest, as the class Insecta. The importance of insects consists in (i) the damage they cause to field crops, orchards, forests, stored products and household materials; (ii) their interference with man’s health and comfort; (iii) their value as (a) pollinators and agents of fruit setting in orchards and crops, (b) suppliers of products like silk, honey and lac, (c) scavengers, and (d) useful parasites and predators; (iv) their remarkable suitability and utility as material for purely scien¬ tific studies, e.g., (a) genetics and inheritance, of which Drosophila is the hero, (b) sociology and population growth, for which ants, termites, wasps and bees have been in the forefront, and (c) adaptability, mimicry, etc., for which the leaf butterfly Kallima and the stick insect are the classical examples. All these and many others represent the diverse ways in which insects are intimately associated with man. Fundamental versus applied Entomology. In practice the term ento¬ mology has an applied significance. Hence, it is necessary to understand at this stage the implications of applied science. The pairs of opposites generally used are ‘fundamental versus applied aspects’, ‘fundamental versus developmental aspects’, ‘academic versus applied approaches’. For a clear understanding, it should be divided into academic and applied aspects. The motto of the academic approach should be, as it has always been, ‘knowledge for the sake of knowledge’. Any aspect which is not known ought to be known, irrespective of and undeterred by any idea
PLACE OF ENTOMOLOGY IN RELATION To MAN
3
about the utility, futility, or even harmfulness of the knowledge thus gained. Any lacuna in knowledge must be filled. This has been rightly the approach of the traditional universities. The approach of the applied institutions, such as the agricultural research institutes or the recently established agricultural universities, has to be rather different; they have to engage themselves in problem-oriented research activities. They have to be sure- that if they are successful in obtaining an information as they expect, it will be definitely useful as planned. First they have 'to identify the problems carefully, and then to analyse them in detail so as to expose clearly the lacunae which must be filled for proper solution of the pro¬ blems. This may call for only some adaptive research for successful ex¬ ploitation of an already known principle under a specific situation, or it may call for a fundamental probe. Hence, the applied aspect should be further divided into fundamental and developmental; the former may be designated as ‘fundamentals of applied aspects’. Alternatively, the science of entomology can first be divided into ‘fundamental and developmental aspects’, and then the fundamental aspect can be subdivided into ‘academic and applied approaches’, the former resulting from the motto ‘knowledge for the sake of knowledge’ and the latter meant to fill up a fundamental lacuna for the solution of a well-identified applied problem. For organizational facilities and for quick scientific solutions of pro¬ blems the former dichotomy is more useful, for it provides better co-ordi¬ nation between developmental and fundamental aspects necessary for the solution of any problem. Science of Entomology
Applied aspects
Academic aspects (Motto : Knowledge for the sake of knowledge)
(Motto : Problem-oriented scientific pursuit)
Fundamental aspects (Aim : To fill up a fundamental lacuna in knowledge for the solution of a wellidentified problem)
OR
Developmental aspects
(Aim : Adaptive research for proper exploitation of a known principle or phenomenon)
4
AGRICULTURAL ENTOMOLOGY AND PEST CONTROL Science of Entomology
Fundamental aspects (Aim : To fill a fundamental lacuna in knowledge)
Applied aspects
Academic aspects (Motto : Knowledge for the
sake of knowledge)
Developmental aspects (Aim : Adaptive research for proper exploitation of a known principle or phenomenon)
(Motto : To fill a fundamental lacuna for the solution of a well-identified problem)
Entomology as an Applied Science
In applied biology, when the aim is economic exploitation of any species, it has to be studied in almost equal depth whether we want to exploit it in a positive or a negative way; i.e. to culture it for increasing its produce as in the case of crop plants or to check its multiplication as in the case of pest species. The number of species of insects is so large (more than 1 million) that the preliminary item of their identification itself is one of the most tedius jobs, for which no single organization in the world is fully equipped. This is an indication of the work load in¬ volved in the solution of pest problems. The entomologist’s interest in various forms of life has to be as varied as the insects he has to deal with, as will be evident from the following examples. 1. Class Mammalia. The dairy, wool and livestock industries are based on this class. Monkeys, jackals, bats, squirrels and rats are serious pests of agriculture. Insects are so much responsible for dis¬ eases of man and livestock that there are separate branches of medical entomology and veterinary entomology. 2. Class Aves. The poultry industry is based on this class. Fruit¬ eating birds such as parrots are serious pests, but some other birds eating in¬ sects are useful. Information on their diet and economic importance is very useful. Entomologists are also interested in insect parasites of poultry. 3. Class Reptilia. A number of reptiles including snakes are very useful in keeping the insect pests under check. 4. Class Amphibia. Some members of this class, e.g. frogs, are useful; they eat insects. 5. Class Pisces. Some fishes eat insects; Haplochilus lineatus
PLACE OF ENTOMOLOGY IN RELATION TO MAN
5
destroys mosquito larvae and has been recognized as definitely useful in the control of malaria. Ophichthy boro, which is a long, flat eel living in tidal streams, has been reported to do considerable damage by burrowing into and making wide passages across the bunds, thus connecting paddy fields containing fresh water with salt-water channels. 6. Class Chilopoda. Centipedes feed on insects and are beneficial although sometimes they inflict very painful bites on man. 7. Class Diplopoda. Some species of millipedes attack growing crops and become serious pests in fields and greenhouses although many feed on decaying vegetable matter. Those that are pests feed on roots or leaves near the ground. 8. Class Arachinda. The spiders (Order Araneida) feed on several injurious insects, and have venomous jaws which poison insects. Sometimes their bites cause serious results. On the whole they are beneficial. Mites and ticks belong to the order Acarina. Some species of mites injure plants, some are parasitic on insects (locusts and grasshoppers). Some are predatory on some insects and mites. While certain species of ticks are parasitic on men, livestock and other animals, some transmit
diseases. Scorpions (Order Scorpionida) bear sting at the tip of the abdomen. They are the best known stingers. Their pedipalps are much more developed and carry a pair of pincers which are used to grasp the prey. They are , predatory in habit. Despite the sting, they may be considered beneficial. 9. Class Crustacea. Crabs, prawns, lobsters and sow bugs are some¬ times injurious in greenhouses. Crabs are known to damage paddy crops, although several species are carnivorous. 10. Phylum Mollusca. Snails and slugs are often serious pests of plants in greenhouses and in fields. 11. Class Nematoda : Roundworms are becoming so important as plant parasites that separate departments of Nematology are coming into
existence. Colossal Damage by Insects
The one facet of insects’ life economy about which, we are seriously concerned is their potentiality for doing immense harm to man’s interests. There is hardly anything that man would like to call his own and insects will not challenge his claim. Taking for example the insect damage to economic plants and plant products, a rather conservative and commonly accepted estimate has been that the average loss caused by insect pests is about 10%. To the nation this means an annual loss of Rs 500 crore 10% of Rs. 5000 crore, which used to be our average annual income from agricultural and forest resources. The great harm done to human
—
6
AGRICULTURAL ENTOMOLOGY AND PEST CONTROL
and livestock health is incalculable, as also its repercussion on the national activity. In spite of their causing colossal losses in various fields of human activity, the minute size of many insects misleads us to a false sense of complacency towards insects in general. If a lion enters a town, the whole town will get thoroughly shaken up, and every effort will be made to kill it immediately, although its potentiality of damage may be only a few deaths. But if a house fly carrying cholera germs enters a restaurant, it can flit about from dish to dish and many people may not even move their finger to scare it away, even though its potentiality for harm may be many deaths through an epidemic of cholera. The dangers from the insect world are often underestimated, and it is seldom realized that in spite of the usefulness of some groups the insects as a class constitute enemy number 1 of the human race. It- is interesting to note that there are ample references even in the most ancient records to the 3 main groups of useful insects which have been providing honey, silk, and lac; and man has preserved them for these valuable commodities. In comparison with such sound study of useful insects the knowledge about harmful insects at that time was surprisingly poor. It is amply clear from various hymns in the Vedas and other ancient literature that, although the pest problems were quite serious, the knowledge about them and their control was meagre. In fact, realization of the dangers from the insect world has been extremely slow all over the world, and the science of entomology came into being more as a result of the hobby of amateur insect collectors than from the labours of professional economic scientists. In India this realization has been even slower, probably because of the religious beliefs and abhorrence of destroying life and certainly because of little interest in insects even as a hobby. In this connection it is instructive to recall the Mahabharata story of sage Mandavya who developed the habit of collecting and pinning insects; for this crime he had to pay the penalty of his life by being himself impaled on the point of "a crowbar. Our public is still unsympathetic to activities of entomologists and expects only simple, harmless and cheap methods of keeping away from their crops and crop produce what they would like to call mere insect nuisance. Thus, there exists a puzzling, yet interesting, anomaly. I wonder if any attempt has ever been made to appreciate and explain this anomaly. Careful scrutiny of the whole situation suggests 2 explanations. The first is somewhat simple. The pest problems of agriculture, for example, arose with the origin of agriculture, and became aggravated with the intensification of agriculture. Therefore, one can say that pest problems could not have been so serious when agriculture
PLACE OF ENTOMOLOGY IN RELATION TO MAN
7
itself was in its infancy. Similarly, epidemiological studies on insects of medical and veterinary importance have shown that the incidence of insect-borne diseases increases with increase in population density of human beings and livestock. Thus, one can also say that the harm done even by such insects might not have been so serious in the early days of human civilization. These arguments only partly explain the anomaly but provide full and convincing answer to the query why insect problems are multiplying with increase in the number of entomologists. The other subtler explanation is that insects have been exploiting their characteÂŹ ristic minuteness for dodging humanity and their other enemies and cutting them in a sort of complacency or false sense of security against them. In this way the- insects have been ensuring the success of their struggle for existence. Generally, however, insects are neither so minute as to be invisible to the, naked eye and thus to create a sort of blind awe, nor large enough to create a visual impression about the magnitude of their seriousness, except under certain special circumstances, e.g. locust
invasion.
CHAPTER 2
DOMINANCE OF INSECTS
INSECTS came into existence, according to various estimates, 250~500 million years ago. The antiquity of this can be gauged from the fact that man came on the scene only 1 million years ago. Ever since such an early geological epoch insects have held their own against all odds and, as a result of their struggle for existence for so long, today they constitute the most dominant class of the animal kingdom. They also represent the culmination of evolutionary development in terrestrial arthropods. Size of the class Insecta. Insects constitute the largest class not only of the animal kingdom but also of the whole living world. The number of known species of infects is much more than that of all other species of the animal kingdom put together. Estimates of both the absolute number of insect species and their relative proportion vary from 700,000 to 1,500,000 species, and from 70% to 90% of all known species of the animal kingdom. According to Metcalfe (1940),* the knowledge about animals has been growing during the last 200 years. In 1758, when Linnaeus established the binomial nomenclature, he described only 312 genera and 4,203 species of animals of all classes. Of these, 74 genera were of insects, with 2,102 species. In 1902, Sherbom listed all animals described between 1758 and 1800, and his list included 3,234 genera and 58,833 species. Since 1850 the annual publication ‘Zoological Records' is quite a reliable source of in¬ formation. On counting the number of new species published in these records every 10 years it was found that on an average 10,542 new species of insects and 7,253 ©f other animals were described annually. If these averages are correct, they give a total of 948,780 species of insects des¬ cribed between 1850 and 1940, and 652,770 species of animals other than insects. This appears to be the most reliable of the available estimates, although Metcalfe tried 2 other methods, and found the average of the 3 estimates to be 1,500,000 species of insects. Size of Individual Insects. Insects as a class are very small individuals. In fact, they include the smallest forms of animals with free and active aerial life. No other animal group has been able to evolve forms so small in size as some of the insects and yet be capable of leading a free aerial existence. There are some microscopic spores, of both animal and plant origin, but they are non-active resting stages which are blown about by the wind. All the same, the size of insects varies widely. An appealing *
Metcalfe, Z. P. 1940. Ent. News 51 : 219-222.
9
DOMINANCE OF INSECTS
statement about the size variation in insects is that some are smaller than the largest Protozoa, the phylum which contains the smallest, singlecelled animals; and some are larger than the smallest Yertebrata, the phylum which contains the largest animals. The following are some of the insects which represent these extremes.
1. The largest insects Coleoptera Megasoma elephas
— — — up
120 mm Macrodontia cervicornis 150 mm
Orthoptera
Pharnacia serratipes to 260 mm (length) Hemiptera Belostoma grande up to 115 mm (length) Lepidoptera Erebius agripinna 280 mm (wing span) Attacus atlas 240 mm (wing span) Odonata Moganeura (fossil from Upper Carboniferous Strata) 600 mm 2. The smallest insects Coleoptera Trichopterygidae 0.25 mm Hymenoptera Mymaridae smaller than Trichopterygidae
—
— —
—
more than
—
—
Population of Individual Species Nobody has attempted to assess the population of the various insect species Sn the world. It is, however, interesting to note that whereas the population of human beings is 3 to 4 thousand million in the world it is negligible in comparison with the population of any species of insect pest. For example, the population of aphids in a mustard crop was esti¬ mated as more than 40 million of individuals per acre. Thus, of the 3 criteria, viz. the size, the variety, and the population density, the insect class can unquestionably claim dominance on the basis of the last 2. In size of individuals, the insects may seem to be at a dis¬ advantage, but small size is highly advantageous for survival in the struggle for existence.
Secrets of Insects’ Inherent Strength and Dominance Apart from their small size, insects as a class have acquired many structural, developmental and behaviouristic perfections not found in any
10
AGRICULTURAL ENTOMOLOGY AND PEST CONTROL
other group of animals or in plants; the significance of these has yet to be fully appreciated even by entomologists. The following are the cha¬ racteristic features that contribute to the insects’ dominance as a class. Structural Perfections
Exoskeleton. This is a characteristic of all arthropods, but insects seem to have fully exploited the mechanical advantage of their exoskeleton; for it not only provides! a much larger area for the attachment of muscles but also protects the muscles from mechanical injury. Moreover, it affords an excellent mechanism to protect insects against desiccation. But for the very effective waterproofing efficiency of the exoskeleton, probably such minute animals as most insects are could not have evolved so successfully even as terrestrial forms, much less as aerial ones. No other form of life with such minute size has been able to lead active aerial existence. The main disadvantage of small size is the comparatively large surface area per unit body weight; this means greater vulnerability not only to mechanical injury but also to desiccation. Insects have successfully over¬ come both these difficulties by virtue of their exoskeleton. In addition, the exoskeleton has turned the appendages into good tools for digging, preying, and oviposition. Lastly, the exoskeleton maintains the shape of the body much more efficiently than the endoskeleton; old age is unable to affect the form of adult insects, and even death does not necessarily deface the beautiful shape of the live insects. How far this advantage has contributed to insects’ success in the struggle for existence is difficult to assess, but it has certainly made the job of insect collectors easy. Some important corollaries mentioned below have followed the development of the waterproof exoskeleton. (i) Small size : The evolutionary course followed by insects has led to the development of a large number of smaller individuals rather than a small number of larger individuals. Undoubtedly, this immensely increases the chances of survival of the species; for the larger the number, the greater the survival chances; and the smaller the size, the easier for indi¬ viduals to subsist on small quantities of food and to take refuge in small niches against the vicissitudes of weather and against adverse biotic agencies. With larger numbers resulting from smaller size the chances of variability and mutation also increase, thus making it possible for nature to conduct a larger number of trials in evolution. Lastly the smaller size leads to greater efficiency. It is one of the biokinetic principles that the contractile power of muscles depends on their cross-section, i.e. area as square of a linear dimension, or a unit with 2 linear dimensions; the weight on the other hand depends on the cube, i.e. on a linear dimension raised to the power 3, or a unit
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