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GORTERIA JOURNAL ISSN: 0017-2294 K. T. Sidheek Comparative studies on odonata diversity in mangroves and paddy field ecosystems of Malappuram district, Kerala, South India. Abstract: Abundance and diversity of odonates were studied in two different ecosystems of Malappuram district, Kerala, in varying seasons, pre-monsoon, monsoon, and post- monsoon, during March 2019 to February 2020. The ecosystems studied were paddy field and mangrove ecosystem. Paddy field was located in Kottakkal and mangrove ecosystem was located in Kadalundi. In both ecosystems a total of 34 species of odonata including 15 Anisoptera (Dragonflies) and 19 species of Zygoptera (Damselflies) were recorded, which accounts 22.07% of total species of odonates found in kerala. The Libellulidae is the dominant family among Anisoptera. Among Zygoptera the dominant family was Coenagrionidae. The study was carried out by recording dragonflies observed using the line transect method. The study mainly aims the extent of pollution in two different ecosystems because odonates act as indicator of pollution. In two study areas, Kottakkal is more urbanised than Kadalundi. From this study we can observe that 66.6% species (Damselflies and Dragonflies) are observed from Kadalundi and 33.3% are observed from Kottakkal. This study shows the effect of environmental pollution and other human interferences on odonates. Key words: Odonata, paddy fields, mangrove ecosystem, diversity indices. VOLUME 34, ISSUE 4 - 2021 Page No: 150 GORTERIA JOURNAL ISSN: 0017-2294 INTRODUCTION Biodiversity is defined as the variety of and variability in flora and fauna in an ecosystem. Since rapid species extinction occurs in India, documentation of biodiversity is a necessary step to be taken. Basic tool for the study of biodiversity is the taxonomy. Making taxonomy, a combined study will help experts and non-biologists to take identification of species as a hobby, passion and love for nature with support coming from trained scientists (Pisupattu 2015). Generally biodiversity studies are given to higher forms like mammals, birds, reptiles, amphibians and fishes, while lower forms like insects are neglected. Insects constitute 75% of the global faunal biodiversity. Among all the wide variety of insect life on planet, Dragonflies (Anisoptera) and Damselflies (Zygoptera) are the ancient groups to develop wings for first time and venture into air. Both are included in order Odonata. Biodiversity of an insect in an area depends on the nature of the particular area. Insects in order Odonates are found near water ponds, lakes, canals, streams, rivers and swamps. Nowadays the biodiversity of insects declines gradually. The main cause for this declination is pollution. Urbanisation is one of the main drivers of ecosystem change. From rural to urban, the gradient of pollution increases, thereby the diversity of dragonflies and damselflies also varies in different areas. Urban areas are well developed in which density of human interferences like houses, buildings, roads, bridges and railways. Rural area is open land with less human interference. And there is another area semi urban which is partly urban; between urban and rural. The area is somewhat but not wholly characteristics of urban area. So as the human manipulation increases in agricultural lands, water resource, it results in the pollution rate increase and thereby the biodiversity in that area get destructed. So it affects the diversity of dragonflies and damselflies also. The term Odonata, which came from the Greek word ‘odonto’ which means strong teeth found on the mandible of adult. They first appeared during the Carboniferous era, about 250 million years ago. In the pre historic times they were as big as hawks. In those times they had a wingspan of thirty inches and were the largest insects ever to have lived (Boyd, 2005). VOLUME 34, ISSUE 4 - 2021 Page No: 151 GORTERIA JOURNAL ISSN: 0017-2294 Based on morphology, dragonflies and damselflies can easily be distinguished in the field. Damselflies are similar to dragonflies except possessing equal wings that are normally held open when at rest, comparatively weak fliers and eyes are well separated. However, in the larval stage they can be easily distinguished from dragonflies due to the presence of three externally visible gills on abdomen and having cylindrical, fragile body. Odonates vary in their habitat requirements. The life history of odonates is closely linked with water bodies. The larvae tend to reside in flowing as well as in standing waters (Corbet, 1962). The adults are generally found at or around fresh water, although some species roam widely and are possibly found far from their breeding sites. Even though most species of odonates are highly specific to a habitat, some have adapted to urban areas and make use of man-made water bodies. Odonates are Hemi metabolous (i.e. incomplete metamorphosis) insects with three stages- egg, larva (naiad) and adult. Odonates lay their eggs in a wide range of aquatic habitats, from damp soil to waterfalls. Females select the egg-laying site mainly by physical characters. Many dragonflies lay their eggs either in flight or by perching on an overhanging vegetation or rock. Eggs are rounded or spindle shaped, pale yellowish in appearance, which are deposited in plant tissues, floating debris and in submerged or partially submerged vegetation. Eggs are laid in successive batches: a damselfly lays about 100-400 eggs and dragonflies, usually about several hundreds to thousands per batch. Eggs hatch in 5-40 days in the tropics. Damselflies insert their elongate and cylindrical eggs into aquatic plants. Their elaborate ovipositor is serrated and adapted for making incisions in the tissues of plants and placing the eggs in them. The larva is a sophisticated predator. Their cryptic colouration and keen eyesight make them an effective predator. Larvae are a generally silent predator that is they wait for their prey to come close before striking. But some systematically stalk their prey much like birds of prey or as tigers do. When they are in the striking range they shoot-out their formidable jaws which virtually attack the prey. Last instar larvae of bigger species are known to catch even small fishes and tadpoles. In dragonflies, rectum is modified into foliations or rectal gills which are the respiratory organs. In damselflies, foliaceous lamellae are at the end of the abdomen. The number of larval instars is variable within and between species and is usually 9-15. When they are ready to moult, VOLUME 34, ISSUE 4 - 2021 Page No: 152 GORTERIA JOURNAL ISSN: 0017-2294 stop feeding and crawl up to emergent vegetation or rock. This usually happens after sunset and the larvae moult into adults just before sunrise. The newly emerged adults are wet and delicate, and as the day warm up, they become dry and fit for their first flight. Newly emerged odonates leave their emergence site and inhabit nearby landscape. Damselflies complete their maturation period in about a week or less whereas dragonflies take approximately two weeks. During the maturation period, sequential changes occurring the colour of the body and wings. Adult dragonflies are aerial predators and catch insects like mosquitoes, midges, butterflies, moths, bees and odonates on flight. Most of the dragonflies are day flying but a few actively hunt during twilight hours. In this, they resemble insectivorous birds like flycatchers and swifts respectively. They feed in flight, using the legs to capture the prey and transfer it to the jaws. The legs are highly specialized for this purpose, particularly with regard to its position, relative length, articulation and complement of spines. Their vision is well developed and as far as dragonflies are concerned, most of the head is made up of compound eyes. Odonates flying skill is diverse from all other groups of insects. Odonates have uncoupled wings, that are forewings and hindwings are unattached to each other and they beat independently. The powerful thoracic muscles help them in long sustained flight. Odonates can hover and turn 180° while in flight and can fly backwards. Dragonflies are stronger fliers than damselflies and they can reach a speed up to 25-30 km per hour. The difference in flying abilities influences their dispersal and geographic distribution. Some weak fliers are dispersed by wind. Like many other organisms, dragonflies also migrate. One of our most common species, Pantala flavescens migrates immediately after the monsoons. Most odonates are sexually dimorphic when they mature. Males acquire bright colouration as they become sexually mature. Sexually matured dragonflies return to breeding habitat from their foraging. Usually males mature earlier than females and reach the breeding habitat first. They hold a territory and these resident males show aggressive behaviour towards conspecific males, which enter their territory. A receptive female adopts a characteristic posture towards a potential male and pairing follows immediately. The last abdominal segments of the male have claspers, which are used to hold the female by her prothorax. During copulation or just before that, the male transfers his sperms into an accessory genital organ at the second abdominal segment. Both the VOLUME 34, ISSUE 4 - 2021 Page No: 153 GORTERIA JOURNAL ISSN: 0017-2294 partners curve their abdomens so that the genitalia of female become attached to the male’s accessory organ, by doing this; they make a characteristic wheel position. Odonates are unique among all the other insects on the basis of their mating style with this specialized wheel position. Odonates have been a focus of extensive research in many countries. They are one of the few insect orders that have been intensively studied in the tropics (Woodward, 2001). In 1987, Elzinga reported 5000 species of Odonata around the world. But this record was updated by Trumann and Rowe during the year 2001, according to them there are approximately 6500 named species of Odonata so far described all over the world.

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