ODONATA ( INSECTA ) DIVERSITY OF RICE FIELD HABITAT IN PALAKKAD DISTRICT , KERALA

Our infonnation on the odonata (Insecta) fauna of Kerala state, south India has been confined to the works of Fraser (1933, 1934 & 1936) from Kerala part of the southern Western Ghats, Peters (1981) from the Thiruvananthapuram district, Rao and Lahiri (1982) from the Silent Valley National Park, Mathavan et. al. (1989) from the Periyar Tiger Reserve and Emiliyamma and Radhkrishnan (2000) from the Parambikulam Wildlife Sanctuary. There has been no comprehensive study on this insect group from the plains and wetlands of Kerala. In the present study we made an attempt to study the odonata fauna occurring in a paddy field habitat at Palakkad district of Kerala.


INTRODUCTION
Our infonnation on the odonata (Insecta) fauna of Kerala state, south India has been confined to the works of Fraser (1933Fraser ( , 1934Fraser ( & 1936) ) from Kerala part of the southern Western Ghats, Peters (1981) from the Thiruvananthapuram district, Rao and Lahiri (1982) from the Silent Valley National Park, Mathavan et. al. (1989) from the Periyar Tiger Reserve and Emiliyamma and Radhkrishnan (2000) from the Parambikulam Wildlife Sanctuary.There has been no comprehensive study on this insect group from the plains and wetlands of Kerala.In the present study we made an attempt to study the odonata fauna occurring in a paddy field habitat at Palakkad district of Kerala.
Rice fields are excellent habitats for the study of odoantes, as such areas are ideal foraging grounds, with more open environs, providing a large number of insect pests (prey-population) for the odonates to predate upon.Fraser (1933Fraser ( , 1936) ) mentioned 3 species of odonates from paddy fields of Bangalore.Kumar and Prasad (1977) recorded 10 species from the paddy fields of.Dehradun valley.Krishnaswamy et. al. (1984) reported 8 species of odonates predaceous on known insect pests of paddy from Assam.Recently Gunathilagaraj et. ai. (1999) listed 16 species from the rice fields of Coimbatore.Asaithambi and Manikarasagam (2002) recorded Thoiymis tillarga (Fabricius) from paddy field near Annamalai University area in Tamil Nadu.Talmale and Kulkarni (2003) have reported 19 species of odonata from the paddyfield of Bhandara district of Maharashtra.

STUDY AREA
Palakkad (Palghat) is known as the 'rice bowl' of Kerala.This district, centrally located in the state, with its close proximity to Western Ghats is having extensive paddy fields.The present

RESUL TS AND DISCUSSIONS
Altogether 21 species under 18 genera of 5 families were recorded during the study.Of these, 6 species are additions to the odonate fauna of the rice-field habitats of India.5 species were seen throughout the study.Maximum species richness was seen during the harvesting stage.Diversity and richness of species observed in three different stages of the paddy-crop are summarized in Table 1.

GROWING STAGE
When the plant is two-month old, most of the insect pests were found active, feeding on tender shoots and leaves of the paddy plants.5 species of damselfly and 8 species of dragonfly dominated at this time.The most common species found were Ceriagrion coromandelianum, Ischnura aurora aurora, Orthetrum sabina sabina, Brachythemis contaminata, Diplacodes trivialis and Pantala flavescens.During this stage, breeding of Ceriagrion coromandelianum was observed among the adjoining marsh-vegetation near paddy fields.Copera marginipes, Vestalis gracilis, Trithemis  paliidinervis, Tramea limbata and Tholymis tillarga were found in the habitat only during this stage.On many occasions, species such as Pantala flavescens, Tholymis tillarga and Diplacodes trivialis were found attracted to electric light adjacent to the paddy fields.Pseudagrion rubriceps and Copera marginipes were observed ovipositing on the submerged plants in the irrigation canal along the paddy fields.

HARVESTING STAGE
During this stage, 15 species of odonates were observed which include 7 damselflies and 8 dragonflies.Large swarms of Pantala flavescens were observed soaring over the mature paddy plants.Besides Pantala flavescens, the species commonly observed were Ceriagrion coromandelianum, Ischnura aurora aurora, Aciagrion occidentale, Lestes elatus, L. malabarica, Orthetrum sabina sabina, Brachythemis contaminata and Diplacodes trivia lis.During this stage Lestes elatus and L. malabarica were observed only for a brief period of time.Trithemis aurora, Neurothemis intermedia intermedia were found sparingly, only for a few days.Immediately after the monsoon, the waterlogged fields were found attracting many species of odonates for breeding and foraging.Frequent courtship flights of Ceriagrion coromandelianum and Aciagrion occidentale could be noticed during this stage.
Paddy fields being temporary wetlands with periodically changing microhabitat characteristics, the odonate community exhibits variation in species diversity, in accordance with the changes.
The community variation in odonates between stages of the crop indicates the seasonal fluctuation of the odonates frequenting the entire field.The present study shows that the species richness and abundance of odonates were maximum during the harvesting stage.The rain-fed field conditions and the abundance of prey species could be the reasons for the odonate diversity.
Multivolatine species such as Ceriagrion coromandelianum, Ischnura aurora aurora, Brachythemis contaminata, Diplacodes trivialis and Orthetrum sabina sabina were recorded throughout during all the stages of the crop.O. sabina sbaina was found to be the most voracious feeder of the insect pests as observed by Fraser (1936) and Gunathilagaraj et. ale (1999).According to Krishnaswamy et.al. (1984), O. sabina, P. flavescens, I. aurora, A. pygmaea and C. coromandelianum are predaceous odonates of rice-field habitats in Assam.
A perusal of literature and prsent study reveals that altogether 41 species of odonata occur in rice-field habitats of India (Table 2), which include 6 species recorded during the present study, for first time from a rice-field habitat.The data presented in Table 2 also reveal that the most frequent species of odonates in the rice-field ecosystem of the country are Ceriagrion coromandelianum, Ischnura aurora, Agriocnemis pygmaea, Orthetrum sabina, Brachythemis contaminata, Crocothemis servilia and Pantala flavescens.
study area Nanniode, a small village, situated at Perumatty Panchayat about 25 kms south-east of Palakkad town is located at a latitude of 10° 42' N. and a longitude of 76° 47' E. Due to the influence of the Western Ghats mountain ranges and the Palakkad Gap, the area experiences a characteristic climate of severe summer with gusty winds during March to May and plenty of rains during June to November received through the both the southwest and northeast monsoons.Traditionally, two yields of crops are taken annually.The lush green paddy fields, interspersed with banana crops, coconut and Palmyra groves, and bordered with herbaceous weeds along the field bunds, contribute good habi tats for the foraging odonates.METHODOLOGY During the current study, three field surveys spanning 20 days each were carried out in August-September, 1999 (First Harvesting Stage), December-January, 1999-2000 (Second Growing Stage), April-May, 2000 (Second Post Harvesting Stage).Only the adult odonates were collected from the paddy fields, adjoining water bodies and irrigational canals.The observations were categorized according to their abundance, as indicated below : A = Abundant-More than 30 examples observed.VC = Very Common 16-30 examples observed.C = Common 4-15 examples observed.R = Rare 1-3 examples observed.

Table 1 .
: Showing Odonata diversity in different stages of the Paddy at Palakkad.

Table 2 .
: Comparative biodiversity of odonates studied in rice-fields of various states in India.