Mayflies (Ephemeroptera) of the Concho River, Texas

Abstract

The mayfly fauna of the Concho River, Texas, consisted of 17 species in 7 families as determined from 12 collecting sites sampled at least once monthly for two years for both aquatic nymphs and aerial adults. Nymphs were reared to adults for positive association. Leucrocuta maculipennis (Walsh) is reported from Texas for the first time. Adult descriptions of Leptohyphes packeri Allen and Leptohyphes vescus Allen, previusly known from only the nymphal stage, are presented. Prior to this study only two species of mayflies had been reported from the Concho River, Texas, Callibaetis montanus Eaton and Isonychia sicca Eaton (Traver, 1935). Although a number of species of mayflies are reported from Texas, their distributions in the streams of the state are largely unknown. Only two studies of the mayfly fauna in Texas' rivers have been made. Moore (1950) listed the species collected in Dallas County and in the major rivers between Dallas and San Antonio. Due to the poor taxonomic knowledge of the mayfly nymphs at that time his survey is of limited value. Peters (1977) provided a study of the nymphs of the Guadalupe River in central Texas. STUDY AREA-The Concho River is part of the upper Colorado River drainage basin. Permanent streams are located in Concho, Tom Green, and Irion Counties of Texas. The area is a transition zone containing parts of two biotic provinces, the Balconian and Kansan (Blair, 1950). Elements of the Chihuahuan Province are also present. The river system is divided into three sections. Five streams, the South Concho River, Middle Concho River, Dove Creek, Spring Creek, and Rocky Creek are included in the upstream section to the west and south of San Angelo (Fig. 1). The streams originate as springs and seeps along the eroded northwestern margins of the Edwards Plateau from Cretaceous limestone and resemble other springfed streams of the Edwatds Plateau. Stream flow alternates between shallow pools and riffles with the substrate varying from cobble and gravel to limestone bedrock. Eight sampling sites were located in this section of the system. Water from these streams flows into a manmade impoundment, Twin Buttes Reservoir, located just southwest of San Angelo. The middle section of the system includes Twin Buttes Reservoir, Lake Nasworthy, and the series of impoundments produced by small dams through the city of San Angelo. No regular sampling sites were established in this section because of the paucity of mayflies in this disturbed, urbanized area. In addition, no regular sampling sites were located on the North Concho River. The river flow is intermittent; it is dependent upon rainfall rather than springflow. The Concho River from San Angelo to its junction with the Colorado River flows through an area known as the Lipan Flat. It is largely an alluvial outwash plain of Pleistocene age and is extensively cultivated. The river still alternates between pools and riffles but deposition of sediments in pools and behind numerous small dams is increased. Three sampling sites were located in this section. An additional site was located on the Colorado River downstream from the junction of the Concho River. METHODS AND MATERIALS-Collections were made at least once monthly at all collecting sites (Fig. 1) from May 1979 to March 1981. Nymphs and adults were collected. Nymphs were preserved in 90% ethyl alcohol and adults in 70% ethyl alcohol. Nymphs were obtained by hand picking and by use of an aquatic dip net. Positive association between nymphs and adults was This content downloaded from 157.55.39.170 on Sat, 23 Jul 2016 04:45:24 UTC All use subject to http://about.jstor.org/terms FIG. --Study area and location of primary collection sites. er I D