There is extensive research of the Ephemeroptera communities taxonomy and ecology in the Andean region of Colombia. However, other regions such as the Orinoquia have been insufficiently studied. From this region, in the Meta department, four species have been registered: Varipes lasiobrachius Lugo-Ortiz & McCafferty, Coryphorus aquilus Peters, Miroculis (Atroari) colombiensis Savage & Peters and Tricorythopsis rondoniensis (Dias, Cruz & Ferreira). The main objective of this study is to report for the first time for this region the species: Mayobaetis ellenae (Mayo), Hydrosmylodon primanus (Eaton), Haplohyphes baritu Domínguez, Camelobaetidus edmundsi Dominique, Mathuriau & Thomas and Nanomis galera Lugo-Ortiz & McCafferty.

Se corrigen las palabras clave así: Palabras clave: Distribución, Andina-Orinoco, pie de monte, taxonomía.

The mayflies are insects widely known as indicators of aquatic quality in freshwater systems, they are abundant and diverse in tropical streams. In this study, it was determined the influence of physical, chemical and bacteriological characteristics on the Ephemeroptera assembly in a period of low precipitation in the Ocoa river of Meta department. There were 5,332 nymphs belonging to 4 families, 10 genera and 3 species. Three new genera records and one species are presented for Meta: Cloeodes, Zelusia, Lumahyphes and Americabaetis alphus. The genera Camelobaetidius and Varipes were found associated with conditions of contamination by organic matter and water mineralization. Likewise, Americabaetis, Thraulodes, Lumahyphes and Tricorythodes were associated with contamination conditions, especially with nitrites and nitrates. Nanomis, Cloeodes and Zelusia showed greater sensitivity to the contamination condition and were related to high percentages of dissolved oxygen in the water and they were in the sampling stations of the upper part in the river. It is important to mention that there were not Ephemeroptera in most of the stations associated with the urban area. That reflects their high sensitivity to polluting conditions at low precipitation period.

Three species of Camelobaetidius Demoulin, 1966 have been reported from Colombia until now, based on nymphs. We describe a fourth species based on nymphs from the Colombian Orinoco river basin. The new species can be recognized by: 1) labrum narrowly rounded anteriorly; 2) segment II of labial palp with a short rounded distomedial projection; 3) incisors of right mandible with eleven denticles; 4) gills absent from the bases of coxae; 5) tarsal claws with ten denticles; 6) outer margin of forefemur with a row of about 23 long, spine-like setae; 7) posterior margin of tergum IV with truncate spines, and 8) terminal filament almost as long as cerci. [Zoobank URL: urn:lsid:zoobank.org:act:500CF998-8EF3-43E3-BA8B-F062B92768F3]

Hydroptilidae is one of the most diverse families of the order Trichoptera in the world. Neotropical fauna has 36 genera. In Colombia, 14 have been reported in the larval stage and 11 in the adultstage. In the present study, a Byrsopteryx larva is registered for the first time in Colombia. The larvawas found in the Orotoy River (919 MASL), a stream from the foothills of the eastern flank of the country’s Eastern Cordillera (Orinoquia) characterized as waterfall current with riffle on rocks and pebbles, preserved riparian vegetation with open canopy, and clay-loam soil. The water temperature was 19.7 ºC, pH 5.8, conductivity 15.6 uS/cm, and dissolved oxygen 9.1-9.7 mg/lO2. Given the high diversity of aquatic ecosystems and the limited knowledge of Hydroptilidae genera in Colombia, we hope to open the way for new research and discovery of more species in the country.