Faunal Diversity in India: Acari
This is an extract from
FAUNAL DIVERSITY IN INDIA
J. R. B. Alfred
A. K. Das
A. K. Sanyal.
Zoological Survey of India,
( J. R. B. Alfred was
Director, Zoological Survey of India)
The phylum Arthropoda includes a group of animals which, unlike the insects or myriapods, have neither antennae nor mandibles. These are known as chelicerata, of which the class Arachnida makes up the largest part.
Of the nine living orders under Arachnida, the Acari comprising the mites and ticks form a most important group. The acari differs from most arachnids in that somatic segmentation is generally inconspicuous or absent. The mouth parts are contained in a discrete anterior gnathosoma and portion of the body on which legs are inserted (the podosoma) broadly joined to the portion of the body behind the legs (the opisthosoma) to form the idiosoma. Idiosoma bears legs, genital and anal openings. The legs are five segmented with variously modified claws at the tip.
Most of the acarines are oviparous. The eggs are laid singly or sometimes as in ticks, in batches of several hundred eggs. The first stadium called larvae bears three pairs of legs. The later stadia named proto-, deuto-and tritonymphs possess four pairs of legs. Almost all mites complete several generations in a year. The ticks usually have a generation of several months and some may have an annual life cycle.
Unlike other assemblages in the class Arachnida, many acarine groups have evolved far beyond primitive predation. Some are exclusively phytophagous, while others have developed complex parasitic relationships with invertebrate and vertebrate animals. Many are also beneficial to man as decomposers and predators. The mites and ticks may be found in virtually any environment including severe desert and tundra situation, mountain tops, deep soil layer, subterranean caves, hot springs and ocean floors. The mites have colonized almost every terrestrial, marine and fresh water habitat known to man. The high degree of habitat diversity illustrated by the mites and ticks is no more remarkable than is their range of form, size, structure and behaviour. The size of mites vary from 1.5 to 16 mm and ticks from 1.7 to 12.7 mm. Engorged individuals of tick may attain 20-30 mm.
The fossil evidence of Arachnida in general or of the Acari in particular indicates that a major adaptive break through occurred in Acari during the late Mesozoic and early Cenozoic era. The acarine radiation may have been stimulated by an "evolutionary synergism" between radiating biota during the late Mesozoic period. During this time, tremendous development of angiosperm plants and a concomitant speciation "explosion" of the insects, a group with which the Acari have close ecological ties had occurred. Most of the acarologists believe that the Acari evolved from some primitive arachnid stock and branched into two separate entities as Acariformes and parasitiformes.
Status Of The Taxon
Global and Indian Status
The existence of mite was referred to as early as 850 B.c. by Homer. The term 'Akari' or mite was originated in 1650. The first consolidated list of mite was given in the book 'Systema Naturae' by Linnaeus (1758). Later this group of arachnid was extensively studied by hundreds of workers throughout the world. The earlier record of the study of mites in India was made as far back as 1868 when Peal discovered prostigmatid mites on tea in Assam and named it as red-spider. The Indian ticks were taken up for research as early as 1758 by Linnaeus. Later more than thousand of papers on taxonomy, ecology, bionomics, physiology, management and other aspects of acarina have been published by nearly hundred acarologists in India.
Though no attempt has been made by anyone to estimate the total number of species from the world but it is presumed that the total acarine species known from the world is not less than 30,000 (Krantz, 1978). The total number of acarine species so far known form India is estimated as 2,186 distributed over 643 genera and 207 families (Table 1). Of these, the prostigmatid mites occupied the highest position in respect of number of species and genera. This is because this suborder contains species that are of significant economic importance. The other suborders in descending order of number of species are Mesostigmata, Cryptostigmata, Astigmata and Metastigmata (Table 1). Nearly 45% of the species so far known from India are described as new to science. Further it is noted that almost all the astigmatid species found in India are cosmopolitan in distribution.
The distribution of acarine species in different States in India is shown in Table 2. It indicates that West Bengal alone represents 19.4% of Indian fauna and occupies highest position among the other States. The second highest number of species occurs in Karnataka. The other States in order of number of species are Tamil Nadu, Maharashtra, Kerala, Delhi, Uttar Pradesh, Tripura, Orissa, Punjab, Assam, Haryana, A & N Islands, Himachal Pradesh, Bihar, Manipur, J & K, Madhya Pradesh, Meghalaya, Andhra Pradesh, Sikkim, Rajasthan, Arunachal Pradesh, Nagaland, Pondichery, Goa, Daman and Diu and Mizoram.
The suborder-wise distribution of species shows that highest number of prostigmatid mites is known from Tamil Nadu followed by Maharashtra and Karnataka. Similarly, maximum numbers of mesostigmatid, astigmatid and cryptostigmatid mites and metastigmatids (ticks) are recorded from West Bengal and Kamataka, respectively. No mite species is so far known from Mizoram and only few ticks have been reported from the States. Several species of cryptostigmatid mites and a few species of metastigmata are known from Sikkim. No variation in present and past distribution of this taxon is observed. The pattern of distribution shown here does not reflect the actual picture as extensive and systematic surveys have not yet been done in many States of the country.
Table -2 Distribution of acarine species in different states of India
Biological Diversity And Its Special Features
A wide range of biological diversity has been observed in this taxon. The class has been divided into five suborders, viz., Prostigmata, Astigmata, Mesostigmata, Cryptostigmata and Metastigmata. The first four suborders include the mites and tick is the sole member of the last suborder. These suborders are further divided into several families, subfamilies, tribes, genera and species, the numbers of which are given in Table 1. The taxon may be divided into eight major groups (Plant associates, soil associates, invertebrate associates, vertebrate associates, storage associates, nest associates, dust associates and water associates) on the basis of habitat preference. Maximum number of genera and species are found to occur in association with plants. The acarines living in soil, occupied the second position in terms of number of species known from India. The total number of species known from vertebrate and water associated groups showed third and fourth position, respectively.
As the acarine fauna of majority of the States of India still remain unexplored (except plant mites) and whatever distributional data available are insufficient, it is rather difficult to make any comment on the degree of endemism in this taxon. However, on the basis of data so far available, it may be noted that the Indian acarine fauna has a number of endemic genera and species. More than 45% of the total species known from India are considered to be endemic. The endemicity is more pronounced in Prostigmata, in which the distribution of nearly 48% of the species known from India are restricted to this country only.
Since the acarines are soil inhabiting animals and associated with agricultural crops, stored products and also parasitic to animals, the chances of their being transperted/introduced from outside cannot be ruled out. The discontinuous or restricted distribution of many genera/species of mites or description/record of speices based on solitary specimen rais doubts about their establishment in India. But there is no record of species introduced in India.
The acarines have achieved tremendous value because of their manifold beneficial as well as harmful effect in agriculture, medical and veterinary sciences, public health and poultry. There are mites which are recognised as very serious pests of agricultural, horticultural and commercial crops. They suck the plant sap and also act as vectors of many plant viral diseases. All these effects reduce the yield as much as 50-80% resulting in economic loss to the extent of several crores of rupees in India. Mites of different families are known to infest stored grains and other stored products. They feed on the germ tissues and surrounding endosperm of the grains, causing serious losses every year. Most of the animals in nature are attracted by different species of mite. These mites either suck blood from the host body or feed on the tissue material, resulting in loss of health and ultimately death of the animal. These mites cause serious loss in poultry and apiculture. There are several mites which are a serious problem to man, for they cause harm to livestock and other domesticated animals. They cause severe mange in cattle, dog, cat, pig and horse. Various helminth diseases caused by anoplocephaline cestodes in cattle and domesticated animals are transmitted by different species of mites. These tiny creatures are also responsible for scabies, tumors, nodules, thickening of skin and other allergic dermatitis, loss of hair, anaemia, pneumonia, scrub typhus, respiratory allergies including bronchial asthma, rhinitis to man, etc.
However, not all mites are enemies of man as there are many who are friends too. Many species of mites are definitely known as efficient and useful predators of the plant feeding mites and can successfully supress their population below economic injury level. Few species also act as predators of soil nematodes. Many of the predatory mites are used as biotic agents for control of housefly and other insect pests. The soil inhabiting mites have drawn special attention because many of these are related to the process of humification of organic matter resulting in increase of soil fertility. The decomposition process of forest litter and the resultant fertility is due mainly to this group of mites. Likewise, there are some water mites which are known to feed upon mosquito larvae and thus check their population.
The other member of the order acarina-the ticks live as ectoparasites of vertebrates and feed obligatorily on the blood of mammals, reptiles and birds. They surpass all other arthropods as transmitters in the number and variety of diseases of man and domestic animals. These acarines cause paralysis and anaemia and serve as reservoirs and vectors for many infective viruses, rickettsias, bacteria, sporozoans and spirochaetes. Ticks are the main vectors of kyasanur forest desease in man and monkeys in Karnataka State. Other arboviruses like Kaisodi, Ganjam and Bhanja are also present in ticks in India.
Most of the acarine species are harmful to human beings, and there is no question of threat for those species. But the economically important species of mites are really in threat due to their habitat destruction. The land is being polluted by pollutants and gradually degraded due to massive felling of trees. As the degraded lands or wastelands contain no orvery little moisture content, the mites inhabiting there are died. Further, excessive and indiscriminate use of chemical pesticides and fertilizers causes the loss of the predatory mites, which control the population of phytophagous mites in nature.
Conservation Strategies And Future Studies
As the population of mites of economic importance is considerably high, the loss of these tiny creatures has not yet attracted the attention of conservationists. But it is high time to formulate strategies for conservation of the taxon for the role they play in maintaining the ecological balance specially in soil ecosystem. So, the destruction of habitat of the beneficial acarines should be checked and the use of poisonous chemicals either in the form of pesticides or fertilizers and discharge of industrial effluents must be controlled.
The studies in the fields like taxonomy of soil mesostigmatid and astigmatid mites, bionomics and ecology of both the mites and ticks are urgently needed. These studies will certainly find out the ways for effective and useful conservation strategies needed for this taxon.
Cook. D. R. 1967. Water mites from India. Mem. Amer. Ent. Inst., 9 : 411 pp. Evans, O. G. 1992. Principles of Acarology. CAB International, UK, 563 pp. Gupta, 5. K. 1985. Handbook: Plant mites of India. Z.5.1., Calcutta: 520 pp.
Gupta, 5. K. 1988. Fauna of India (Acari : Mesostigmata) Family Phytoseiidae, Z.5.1., Calcutta : 350 pp.
Prasad, V. 1974. A cataloglle of Illites of India. Indira Acarology Publishing House, Ludhiana : 320 pp. Prasad, V. 1982. Tile lIistory of Acarology. Indira Publishing House, Michigan, U.s.A. : 472 pp. Sanyal, A. K. and Bhaduri, A. K. 1986. Checklist of Oribatid mites (Acari) of India. Rec. zool. SIITV. India, Occ. Pap. No. 83 : 79 pp.
Sanyal, A. K. and Bharudi, A, K. 1988. The present state of knowledge of Oribatid taxonomy in India. In : Progress in Acarology (eds. Channa Basavanna, G. P. & Viraktamath, C. A.). Oxford & IBH Publishing Co. Pvt. Ltd., New Delhi, 1 : 295•300. Sharif, M. 1928. A revision of the Indian Ixodidae, with special reference to the collection in the Indian Museum. Rec. Indian MilS., 30 (3) : 217•344.