Life cycle studies of Heptageniidae (Insecta: Ephemeroptera) in Kumbbakarai Stream of Western Ghats,Tamil Nadu, India

Abstract

Mayflies (Ephemeroptera) are abundant and diverse in most tropical Asian streams. They represent 30% of benthic populations (Dudgeon 1992) but little is known about their life history. Rawlinson (1939) gave a detailed account of breeding and life history of Ecdyonurus venosus. Harker (1952) studied the life histories of Ecdyonurus torrentis, Heptagenia lateralis and Rhithrogenia semicolorata and found that the last two forms have univoltine life cycle. Epeorus pleuralis was also found to have univoltine life cycle (Minshall 1967). McCafferty & Huff (1978) have given an account of the life cycle of Stenacron interpunctatum. Bengstsson (1981) and Olechowska (1981) described the life cycles of Heptagenia fuscogrisea and Rhithrogena loyolaea respectively. Dudgeon (1996), Salas & Dudgeon (2003) described the life cycles of Heptageniidae, Baetidae and Leptophlebiidae. This short communication deals with the life cycle pattern of Heptageniidae found in Kumbakkarai Stream of Western Ghats (11 0 N & 77 0 50'E) situated about 100km west of Madurai, on the eastern side of Palni Hills at an altitude of 400m. A perennial hill stream cascades as Kumbakkarai falls and water temperature ranges from 25 0 to 35 0 C. This area receives 175 to 210 cm rainfall per year. Materials and Methods Quantitative samples were collected bimonthly during January-December 2006 randomly from ten cobbles of uniform size, in a stratified manner across the stream habitats. Individual cobbles were transferred from the stream bed to a hand net (200μm mesh) positioned immediately downstream, washed inside the net. Larvae collected from all cobbles were pooled and preserved in 70% alcohol. Clifford (1969) method was followed and in the classification of stages, nymphs were grouped into four arbitrarily chosen developmental stages by appearance and development of the mesothoracic wing pads. Stage I nymphs lacked wing pads; stage II nymphs had wing pads but the lengths was shorter than the distance separating the two wing pads. Stage III nymphs had their wing pad length greater than the distance separating the two wing pads. Stage IV nymphs had darkened wing pads. Every stage is represented by several instars with the exception of stage IV, the last nymphal instar, where the tanned wing pads indicate impending emergence. Male and female nymphs were separated by looking at the genitalia and the nature of eyes. Eyes are very close in male; in female they are widely apart.