Insecta: India
Contents |
Faunal Diversity In India: Insecta
This is an extract from FAUNAL DIVERSITY IN INDIA Edited by J. R. B. Alfred A. K. Das A. K. Sanyal. ENVIS Centre, Zoological Survey of India, Calcutta. 1998 ( J. R. B. Alfred was Director, Zoological Survey of India) |
Introduction
The insects are by far the largest group among animals and plants in the world. They are referred to as Patanga, Shalabh, Bhramar, Pipilika, Makshika, Shadpada, Laksha Keet , etc., in ancient Sanskrit writings. It is commonly believed that 75-80% of the total animal species on this planet are insects. They are found everywhere, except in seas and oceans. In this context, factors such as their minute size, high fecundity, capacity for flight and dispersal, ability to feed on variety of materials, water retention capability, presence of chitinous exoskeleton, etc., are important for their survival in different type of ecosystems with success. Thus, both in quality (number of species) and quantity (number of indiViduals) they outnumber all other biota. Insects are related to spiders, crabs, prawns, centipedes and millipedes. Generally their body is composed of three parts: head, thorax and abdomen, with two pairs of wings and three pairs of legs (hexapoda) on the thorax. Mouth parts are either piercing and sucking type, or cutting and chewing type. Head has a pair of antennae and two kinds of eyes-simple and compound. Abdomen is segmented, with last segments modified into genitalia. Sexes are separate. Obviously, there are variations of all kinds and form, as reflected in Table 1. Even some of the common insects may not appear typical. Immature stages (larva) are altogether different in shape and generally worm-like. The life cycle of insects is either (i) egg~ nymph~ adult, or (ii) egg~ larva~ pupa~ adult.
Status Of The Taxon
Global and Indian Status
Insects are predominant biota on all continents including Antarctica. Estimates vary from 600,000 to one million species of insects identified so far which, authorities believe, are a fraction only since a large percentage is yet to be discovered and reported. The beetles alone include some 350,000 species. VARSHNEY: Insecta Insects are believed to have appeared on this planet in the Devonian Period, some 200 million years ago and since survived the glacial periods and evolved into myriad forms. The insect fauna of India is vast. In an old estimate, Lefroy & Howlett (1909) in the monumental book 'Indian Insect Life' reported 25,700 Indian species. Beeson (1961) estimated 40,000 and Menon (1965) 50,000 Indian species. Roonwal (1989) opined that insects constitute two-thirds of the total fauna in India and comprise nearly 100,000 species, of which about half remain yet to be studied. In a recent estimate Varshney (1997) has reported 589 families and 51450 species of insects from India (modified after Jairajpuri, 1991). However, the current corrected figures are given in Table 2, showing 619 families and 59353 species of insects from India.
Distribution
India provides wide range of ecological, climatic and vertical distribution of the insect fauna. The altitudinal variations from sea level to the snowline and above ir\ the Himalaya present a series of zones. The insect distribution is influenced by these vertical zones on account of their vegetation, rainfall, temperature, etc. Right from Mountain Highlands in Jammu & Kashmir, Himachal Pradesh, Uttar Pradesh, West Bengal and Arunachal Pradesh, to desert areas of Rajasthan, Gujarat and Ladakh (cold desert), to tropical Humid Forest areas in Kerala, Tamil Nadu, and N.E. India and to Insular Biomes of Andaman, Nicobar and Lakshadweep groups of Islands, a great variety of insects are known to occur.
The tropical evergreen forests of eastern Himalaya and hills of the north-eastern India harbour maximum number of species. This could be due to the type of vegetation, hot and humid climate and the geographical location of the area, which is a meeting place of the Indian Peninsular, Malaysian, Chinese and Palaearctic regions. A second such rich area is the hills of South India, viz., the Nilgiri, Annamalai, Palni, Caradamom, etc., and the Western Ghats. A third such rich habitat of insects is the western Himalaya, covering foot¬hills and mountainous areas of Jammu & Kashmir, Himachal Pradesh and Kumaon and Garhwal of Uttar Pradesh. With temperate climate and forests of oak, pine, birch, cedar, etc., these areas provide niches for many rare species. It is evident that in the elevated, colder and forested areas of the country, the insect fauna is much varied, colourful and plentiful. Some localities like the Khasi Hills, Sikkim, Darjeeling, Yercaud, Simla, Mussoorie are famous type-localities of a larger number of insect species including some unique ones. The Great Indian desert is comparatively poor than moist deciduous forests. About 20 orders of insects are known from the former area (Roonwal, 1982). There are still areas that have not been adequately explored for its insect wealth. These include Pangi Valley (Himachal Pradesh), Valley of Flowers (Uttar Pradesh), Neora Valley (West Bengal), Tirap (Arunachal Pradesh), Agasthyamalai and Eravikulum (Kerala), etc.
Biological Diversity And Its Special Features
The insects are classified into about 25-30 orders (number varying with different authorities). Some of the Insect orders and the common insects included in them are indicated in Table 1. Table -1 Insect orders with common examples Name of Order Insects included (common names) (arranged alphabetically) Coleoptera Collembola Dermaptera Dictyoptera (Blattaria and Mantodea) Diptera Diplura Ephemeroptera Embioptera Hemiptera Hymenoptera Isoptera Lepidoptera Beetles, Weevils, Fireflies, Ladybirds, Wood Borers Spring tails Earwigs Praying mantids, Cockroaches Flies, Mosquitoes, Gnats, Midges Mayflies Web-spinners Bugs, Leafhoppers ijassids), Aphids, Coccids (Scale insects, Mealybugs), Cicadas, Bedbug Bees, Wasps, Ants, Bumblebees, Sawflies White ants (Termites) Moths, Butterflies VARSHNEY: Insecta Table -1 (contd.) Name of Order Insects included (common names) (arranged alphabetically) Mecoptera Neuroptera Odonata Orthoptera Phthiraptera Phasmida Plecoptera Protura Psocoptera Strepsiptera Siphonaptera Thysanura Thysanoptera Trichoptera Scorpionflies Lacewing flies, Ant lions Dragonflies, Damselflies Grasshoppers, Locusts, Katydids, Crickets Lice Leaf insects, Stick insects (Walking sticks) Stoneflies Psocids, Book lice Stylops Fleas Silver-fishes, Bristle tails Thrips, Fringe-Wings Caddisflies Biological diversity is expressed in the large number of insect species reported from India. Current estimate shows that about 59353 species are already recorded from India, which form merely 6.83% of the world insect fauna (Table 2). It may be pointed out here that two insect orders, Grylloblattodea and Zoraptera do not occur in India, hence left out from this Table. Table -2 Number of Insect Families and Species in India
Table -2 (contd.)
Plecoptera 7 113 2100 5.38 Orthoptera 30 1750' 17250 10.14 Phasmida 8 146 2262 6.45 Dermaptera 7 320 2000 16.00 Embioptera 2 33 200 16.50 Blattariae 12 186 5000 3.72 Mantodea 6 162 2310 7.04 Isoptera 7 253 2000 12.65 Psocoptera 16 90 2500 3.60 Phthiraptera 8 400 3000 13.33 Hemiptera 77 6500 80000 8.12 Thysanoptera 5 693 6000 11.55 HOLOMETABOLA Neuroptera 13 335 5000 6.70 Coleoptera 104 15500 350000 4.42 Strepsiptera 4 18 554 3.25 Mecoptera 2 15 350 4.28 Siphonaptera 8 52 2000 2.60 Diptera 87 6093 100000' 6.09 Lepidoptera 84 15000 142500 10.52 Trichoptera 19 812 7000 11.60 Hymenoptera 65 10000 120000 8.33 TOTAL 619 59353 867391 6.83 This large number of species of insects occur in a variety of habitats. In fact, some habitats have become indicator of respective insect orders, as depicted in Table 3. Table -3 Habitat-wise distribution of some insect Orders Habitat Insects therein
Table -3 koncId.)
Habitat Insects therein
2. Under stones; bark and crevices Protura, Dermaptera, Embioptera, of trees; decaying logs; leaf litter Psocoplera, Coleoptera
3. Drains; godowns; domestic dark and food comers
4. Soil; humus; snow
5. Soil; moss; rotten wood
6. Logs; mud mounds; under stones; ant's nests; wood work in buildings
7. Open grasslands; foliage; crops; on light
8. Book shelves; on wall, behind hanging pictures
9. Near or in water-bodies
10. Garbage
11. Parasitic on other insects
12. Parasitic on skin of mammals and birds
Dictyoptera (Blattaria) Collembola Diplura Isoptera Orthoptera, Hemiptera, Neuroptera, Lepidoptera Thysanura Ephemeroptera, Odonata, Trichoptera, Plecoptera, Aquatic Hemiptera, Aquatic Coleoptera Diptera Hymenoptera, Diptera, Mecoptera, Strepsiptera Phthiraptera, Siphonaptera, a few Hemiptera It will be interesting to note that insects have adapted to the flowering plants (which evolved later than earliest insects) in a big way. A large number of insects feed on plants, including economically important plants and crops. The latter are thus termed as pests. It is for this reason that insects have been called man's worst enemy. A brief indication is given in Table 4 of the insect groups which generally occur on a typical plant part.
Table -4 Insects on a typical plant Part of plant Insects therein Root Stem Leaves Flowers Fruits Grain Different kinds of larvae; beetles; aphids; coccids Stem borers of moths and beetles; other insects on or under bark Bugs of various kinds, including aphids, coccids and hoppers; leaf minerS; caterpillars; ants Honeybee; bumble bee; butterflies; beetles; thrips; syrphid flies Fruitfly and other flies; larvae of moths and beetles; coccids Store-grain-beetles, moths, cockroaches, ants Besides these habitats, insects are also found on fungi, algae, moss, lichen, rotten wood, leaf litter, under logs, under stones, carrions, dung and other excreta, under bark, in books and papers, wood piles, godowns, haystacks, granaries, on or below snow; on electric light; in running and stagnant waters; in clothes and burrows in ground. Some insects make galls and mines in different parts of the plants and live there.
Endemicity
So far there has been no indepth and standard study of the enumeration of endemic taxa of insects in India for many reasons. Firstly, the number of genera and species to be handled is extremely large; secondly, there has still not been thorough surveys conducted for all groups of insects in the entire country; thirdly, a good number of genera and species are "known from their original record only", giving the impression that they are endemic there, which mayor may not be true due to insufficient surveys; and fourthly, the detailed taxonomic studies of all orders and families occurring in India could not be completed for want of experts. Thus, only some superficial estimation have been made on the endemicity. One such attempt was made by the scientists of the Zoological Survey of India in the beginning of this decade, the results of which were published by Ghosh (1996). The number of endemic genera and species given therein is modified and shown in VARSHNEY: Insecta Table 5, based on recent estilllates published in the preceeding articles of the present document. Table -5 Number of endemic genera and species of insects in India. Order
1. Thysanura
2. Diplura
3. Protura
4. Collembola
5. Ephemeroptera
6. Odonata
7. Plecoptera
8. Orlhoptera
9. Phasmida
10. Dermaptera
11. Embioptera
12. Blattariae
13. Mantodea
14. Isoptera
15. Psocoptera
16. Phthiraptera
17. Hemiptera
18. Thysanoptera
19. Neuroptera
20. Coleoptera
21. Strepsiptera
22. Mecoptera
23. Siphonaptera
24. Diptera
25. Lepidoptera
26. Trichoptera
27. Hymenoptera Total
Endemic Endemic Genera Species 12 23 3 12 4 16 22 45 72 6 115 66 77 200 70 3 117 14 14 60 24 86 170 15 16 579 2421 92 520 13 262 923 3100 15 2 15 107 2135 100 1500 5 650 516 9000 2500 20717 Based on Table 5, it may be pointed out that endemic genera are not reported from all insect orders present in India, as has been erroneously stated by Ghosh (1996). Faunal Diversity in India
Threatened Species
Some insect groups in India are now considered endangered and these have been included in the revised lists of 'Schedules' to the Wild life Protection Act, 1972, which have come into force from 2.10.1980 (Anonymous, 1992). These are shown in Table 6. Table -6 Insects in Indian Wild Life Schedules Schedule No. Insect No. of species Group included
1. Schedule I : Part IV Butterflies 126 Dragonfly 1
2. Schedule II : Part 11 Beetles 37 Butterflies 304
3. Schedule IV Butterflies 19
Brief particulars of these insects, order-wise are as follows : Odonata :There is an intermediate suborder between Anisoptera (dragonflies) and Zygoptera (damselflies), called the Anisozygoptera. It is represented in India by a single relict species, Epiopltlebia laidlawi. It was reported from Darjeeling district in the Eastern Himalaya, where it inhabits pools of hill streams. There is no report of it since last 80 years from India, though it has been found in Nepal. Lepidoptera : Species included in the 'Schedules' belong to the butterfly families Amathusiidae, Danaidae, Lycaenidae, Nymphalidae, Papilionidae, Pieridae, Satyridae, Riodinidae and Hesperiidae.
Earlier Varshney (1986) reported that there are 363 rare and 144 very rare species and subspecies of Indian butterflies. Besides butterflies, some large and beautiful moths like the atlas moth (Attaclls atlas) and the moon moth (Actias selene) and their sister species should also be protected. At present, no species of moths is included in the 'Schedules' It is known that some beautiful butterflies and moths are exploited commercially. Coleoptera: Species included in the 'Schedules' belong to the beetle families Carabidae, Chrysomelidae, Cucujidae and Inopeplidae.
Since detailed population studies have not been carried out on majority of invertebrate animals, including insects, it is not possible to clearly demarcate the species threatened with extinction. However, some insect groups are definitely getting rare. Phasmida (stick and leaf insects) are superb examples of mimicry in nature. This group has become exceedingly rare. Other such interesting insects in India include the rare snake fly (Inocellia crassicomis) (Neuroptera), and the curious mole-cricket (Schizodactylus monstroslls) (Orthoptera) with its curled long wings. Among butterflies, two most beautiful ones, the oakleaf butterfly (Kallima) and the Kaiser-e-Hind {Teinopalpus), have been included in Schedule-II. These require inclusion in Schedule -I. The largest Indian butterfly, the birdwing (Troides), has not even been included in the list. To conclude, it is feared that with further environmental degradation such as increasing deforestation, increasing use of chemicals in agriculture, pollution, etc., several taxa of Indian insects will be endangered soon and eventually lost forever if not protected.
Introduced Species
A number of insect species have been introduced in the country knowingly or unknowingly. Whereas some insects have been imported for the biological control of some other insect pests and weeds, there the unintentional introduction of insects often takes place alongwith the transportation of grains, fruits, animals and other goods. One early example of the import of an insect in India is that of the lantana bug, Teleonemia scrupulosa (Hemiptera). This species was introduced about 50 years back for the control of lantana bushes. However, the insect was found to be a threat to the teak plants as well, hence, its culture was stopped but by the next few decades it has spread over the major part of country. In recent times, the erstwhile Indian Station of the Commonwealth Institute of Biological Control introduced a number of parasitic Hymenoptera species and some lady bird beetles for the control of severe coccid and aphid pests. The Department of Plant Protection and Quarantine has intercepted periodically some uninvited insects alongwith the different consignments received at various ports in the country.
Value
Insects are pests of significance on all important crops of cereals, pulses, fibre crops, oilseeds, sugarcane, tea, coffee, vegetables and fruit plants. They cause at least 10% loss to the agricultural and horticultural plants and forest products annually. A rough estimate shows that the country is losing an exchequer of worth Rs. ten hundred crores per year due to injurious insects.
Besides, insects are carriers of diseases in men and domestic animals. For the spread of number of serious diseases like malaria, filaria (elephantiasis), yellow fever, dengue, etc., the insects are primarily to be blamed. However, the beneficial side is no less valuable, as the insects are the pollinators of plants, thus they play an important role in the nature. They serve as food for other insects, spiders, fishes, birds, etc., forming a vital link in the food chain. Among the beneficial insects, three are foremost-the honey bee, the silk moth and the lac insect. There are four kinds of silks produced in the country from different silk moths. India produces the largest quantity of lac in the world, most of which is exported out in one form or other.
For biological control, some insect species which are either predaceous or parasitic on other insect or mite pests have been utilized the world over. Some other insect species have been found useful in the control of weeds like Lantana, 0plIlltia and Parthenillm. There are several other kind of values applicable to the insects in scientific, ecological, economic, ethical and educational fields, too many to be enumerated here.
Conservation And Future Directions
While nature is taking care of its majority biota in its own way, some thought ought to be given by the planners to the protection and conservation of threatened species of insects in various ecosystems. For this purpose, the exploration and inventorisation is a primary step.
Conservation of habitat is equally important in case of insects as in the cases of other animals. Since many insects are forest dwellers, afforestation can help in saving some of the insect species from the danger of extinction. Protection of wetlands from pollution and other human interference will be helpful in safeguarding aquatic insect populations. Insectories as places where insect cultures are maintained, and Insect Galleries of the museums, can be highly educative. For example, bees, wasps and white ants, with their various castes and with actual specimens to observe, can provide a very useful demonstration on the life of social insects.
Nature Clubs can take up the preparation of lists of insects in their area. Such lists are available for every County in England. Films on the role of insects in spreading disease, or on the succession of populations of pest species, or on the apiculture, sericulture and lac culture can prove quite useful. Insects may be minute in size, yet they are big enough not to be ignored on the issues of interaction with man and environment.
Selected References
Anonymous, 1992. The Wildlife Protection Act, 1972 (as amended upto 1991). Second updated ed., Nalraj Publishers, Dehra Dun : 138 pp. Beeson, C.F.C. 1961. The Ecology and Control of the Forest Insects of India and the Neighbouring countries. First reprint ed., Forest Research Institute & Colleges, Dehra dun: 767 pp.
Ghosh, A. K. 1996. Insect Biodiversity in India. Oriental Ins,. Gainesville, 30 : 1-10, Jairajpuri, M.S., 1991. An Overview. In : 'Animal Resources of India: Protozoa to Mammalia : Stale of the Art' Zoological Survey of India, Calcutta : xi-xxvii. Lefroy, H. M. & Howlett, F. M., 1909. Indian Insect Life. Thacker, Spink & Co., Calcutta : 786 pp. Menon, M. G. Ramdas, 1965. Systematics of Indian insecls. In :' Entomology in India (Supplement)' Entomological Society of India, New Delhi: 70-87. Roonwal, M. L., 1982. Fauna of the Great Indian desert. In : 'Desert Resources and Technology' (Ed. A. Singh). Scientific Publishers, Jodhpur: 1-86. Roonwal, M. L., 1989. The imporlance of insecllaxonomy in India. Hexapoda (Insecta Indica), Madras, 1 : 1-2. Varshney, R. K., 1986. Threatened butterflies of the Indian region. In: 'Wildlife wealth of India' (Ed. T. C. Majupuria). Tecpress Service L.P., Bangkok: 104-116. Varshney, R. K., 1997. Species biodiversity. In : 'An assessment manual for Faunal Biodiversity in South Asia' (Eds. J. R. B. Alfred, R. K. Varshney and A. K. Ghosh), SACEP, Colombo: 9-15.
