Spatio-temporal distribution of aquatic insects and functional feeding groups in different stretches of River Jatinga, south Assam, India

The present study investigated aquatic insect community of River Jatinga, one of the major north bank tributaries of Barak River, North east India. The objectives of this study were to find out spatial and seasonal distribution of aquatic insects and their functional feeding groups (FFG). Aquatic insects were collected seasonally in five different stretches of the river. Parameters like taxa richness, insect density, diversity indices, FFG%, riverbed sediment texture and particles sizes were determined. Total 37 and 38 numbers of aquatic insect families belonging to eight orders were recorded in the first and second year, respectively. In both years, the upstream sites with rocky substratum showed higher taxa richness (15) in pre monsoon and density (47.33 +/- 8.5) in winter season than that of downstream sites with sandy substratum. The size of particles gradually decreased from upstream sites to downstream sites. Boulders, cobbles, pebbles and granules mostly dominated the upstream sites (US1 and US2) while boulders and cobbles were totally absent in both downstream sites. Trichoptera, Hemiptera, Ephemeroptera and Diptera were the major orders and the major families were Psephenidae, Elmidae, Baetidae, Hydropsychidae, Leptophlebiidae, Gerridae and Simuliidae. The number of FFG types was higher in upstream sites than that of midstream and downstream sites in both years indicating preference for heterogenous habitat. The predators being mostly tolerant occurred across sites and seasons while sensitive groups like scrapers, shredders were found only in the upstream sites. Predators showed highest percentage (97.56) followed by piercers-herbivores, predators/scrapers (83.33). Canonical correspondence analysis revealed distinctive association between the insect community and particle sizes.