Community Turn Over of Flood Water Arthropods in an Irrigated Rice Ecosystem of Tamil Nadu, India

An investigation on the community turn over of flood water arthropods in weeded and partially weeded rice ecosystems was carried out in a rice field trial conducted at the wetlands of Agricultural College and Research Institute, Madurai, Tamil Nadu during kharif 2000 on four ruling rice varieties. The study revealed that in the first week, the turn over rates of 40.00, 41.17, 33.33 and 47.05 per cent were recorded in weeded plots. But, in partially weeded plots the turn over rates were 42.10, 48.00, 42.85 and 50.00 per cent in MDU 5, ADT 36, ADT 39 and ADT 43, respectively. In the weeded plots there was a decline of community turn over of arthropods, where as the increased trend of turn over was recorded from the first to the last week in partially weeded plots. A total of 23 species of flood water arthropods containing 12, 2, 6 and 3 species of Odonata, Ephemeroptera, Hemiptera and Coleoptera were recorded, respectively, in both the ecosystems. A total of 18 weed species were recorded in partially weeded rice ecosystem. Among them, Cyperus iria, C. rotundus, C. diformis, Ehinochloa colonum, E. crus-galli, Panicum repens, Brachiaria mutica and Eclipta alba were dominant.