Diversity and community turnover of floodwater arthropods in irrigated rice

The diversity and community turn over of floodwater ASD 18, ADT 43, IR 50 and ADT 36arthropods in weeded and partially weeded conditon were studied in a rice field planted with four rice varieties at Madurai, Tamil Nadu. The study indicated that 23 species containing 12, 2, 6 and 3 species of Odonata, Ephemeroptera, Hemiptera and Coleoptera were recorded, respectively. Among them, Agriocnemis femina femina Brauer (damselfly), Dineutus sp., Crocothemis servilia (Drury), Pantala flavescens (Fabricius) and Diplocodes trivialis (Rambur) (dragonfly) were the dominant species under both the conditions but were significantly dominant in partially weeded rice plot. The other species viz., Agriocnemis pygmaea Rambur, Ishnura sp of damselflies, Neurothemis tullia (Drury), Traemea limbata (Desjardin) (dragonflies), Beatis sp. of mayfly, Laccotrephes ruber (Linnaeus) (water scorpion), Hydrometra freeni Kirkaldy (water measurer), Anisops cavifrons Brooks (back swimmer), Dytiscus sp. (diving beetle) and Hydrophilus sp. (water beetle) were less prevalent and observed under both the conditions. The dragonflies viz., Trithemis sp, Rhyothemis variegata (Linnaeus), Anax guttatus (Burmeister) and the giant water bug, Lethocerus indicus (Lepeletiller and Serville) were absent in weeded rice ecosystem and were present only in partially weeded rice ecosystem. The diversity of floodwater arthropods indicated that diving beetle, whirligig beetle, water beetle, water measurer, water scorpion and water strider expressed perfect similarity (1.00) throughout the season. The community turnover indicated that turn of taxa generally increased during tillering stage of rice crop. The succession rate of taxa in floodwater fauna was higher in partially weeded rice than in weeded rice plots. Partially weeded plots had the highest turnover of 70.96, 70.58, 72.22 and 71.05 per cent at 58 days after transplanting (DAT), respectively. The turnover of flood water arthropods had a declining trend in weeded plots and the increasing trend in partially weeded plots through out the season.

Author : M. Kandibane