A Treatise on Dragonflies (Order: Odonata, Class: Insecta) of rice ecosystems in Eastern India

This study highlights the 75 species of dragonfly fauna associated with rice ecosystems in eastern India out of which 15 species were regular and rest were sporadic. From the general taxonomic point of view all the species were grouped under 5 families of under order Odonata. Comparing different body parts the double branching keys were prepared for easy identification of 15 common dragonfly species recorded in rice ecosystems of West Bengal. Each key begins with a couplet (a pair of alternative) and each of which leads to another couplet. Finally the reader reaches the specific identity of species. Free hand drawing of wings of the 50 dragonflies were also used for separate identification of these insect species. In addition to this, different studies were made on courtship and mating, egg laying habitats, nymphal development, longevity, flight capacity of dragonfly to make the study more interesting to the reader. The population build up of dragonfly, favors to certain altitude as well as availability of water which is reverse to the other group of insects. Three different localities were selected at 9.75 m (Chakdaha), 200 m (Cooch Behar) and 1250 m (Kalimpong) of which former two represent an unique physiographic ecological system in Eastern India characterized by extreme diversities of dragonfly inhabiting there. The studies on natural enemies of dragonfly along with their major threats indicated that about 2, 4 and 4 species were critically endangered, endangered and vulnerable in rice ecosystem of West Bengal. Dragonflies are very sensitive to changes in landscape and are reliable indicators of wetland health. Therefore the effective conservation of dragonfly depends entirely on conservation of their habitats. Different studies were made to estimate the role of dragonfly in integrated pest management of rice crop in West Bengal. An investigation was also carried out to find out the crop stage wise diversification of individual predator and found that dragonfly was more diverse during flowering to ripening stages of crop respectively. The values Simpson and Shanon diversity index showed that dragonflies are specific flowering to ripening stage of crop. Subsequently the value of Margalef index and Menhinick index also indicated that the aforesaid predators were more diverse in flowering stage of crop whereas it was least in vegetative stage of crop. From the Hill's diversity the number of abundant and most abundant species was calculated where maximum and minimum were obtained from dragonfly and staphylinid respectively. The studies on colonization and succession of major dragonfly taxa in the rice field indicated that it followed a uniform pattern in relation to growth stages as well different phases in the rice field. The studies on relative abundance of dragonfly in different ecosystems reflected that their population in fields could be conserved and enhanced through maintenance of rice weed flora on bund or allowing ratoon rice after the rice crop during fallow period. The fallow land has limited effect on incidence of insect predator in rice crop. The relative ranking chart of 50 important predators in rice ecosystem of West Bengal indicates that the insect belonging to Coleopteran (17) were top of the list whereas dragonfly was third (10). The validity of chart may increase over time and they will need to be updated periodically.