Virgin mayfly
Ephoron virgo (Olivier, 1791)
Polymitarcis virgo (Olivier, 1791): Russev, 1957: 555.
Order Mayflies (Ephemeroptera)
Family Pale burrowing mayflies (Polymitarcyidae)
Conservation status: in Bulgaria: Extinct EX.
General distribution. Spain, France, Belgium, Germany, Italy, Austria, Hungary, Romania, Bulgaria, Southern Russia.
Distribution and abundance in Bulgaria. It is known from 18 localities in the interior rivers (few specimens between 1950 and 1987) and from about 20 localities along the Bulgarian section of the Danube (more numerous subpopulations) [1, 2, 3, 4]. For the last time, it was recorded in the Bulgarian section of the Danube in 1971 [5]. In the interior rivers, it has occurred in tributaries of the Danube (Ogosta, Iskar, Osam, Yantra), in Tundzha (and its tributary Popovska River) and rivers from the Black Sea basin (Kamchiya, Sredetska, Veleka). The last records of the species are from Southeastern Bulgaria: Popovska River near the village of Dobrich in the area of Elhovo, in June 1987, Sredetska River at Debelt Village near Grudovo in June 1987, Veleka River at Gramatikovo Village near Malko Tarnovo in August 1983. During current investigations of these rivers and localities, the species has not been recorded [6, 7, 8, unpublished data].
Habitats. The larvae are burrowing. Typical inhabitants of large rivers with clay-sandy bottoms [1], they prefer a mixed substrate composed of larger and finer materials [9]. They live on or in the river sediment where they dig out U-shaped tunnels.
Biology. One generation yearly. In winter, the eggs are in diapause that terminates in the spring with the rise of the temperature [10]. The nymphs feed on detritus and algae that they filtrate from the water. After their development to the last instar, they swim out onto the surface and fly away, developing into a subimago and then into an adult. The adults swarm over the rivers after dusk (August and September) [1]. They mate in flight, after which the females lay about 2000-3000 eggs on the surface of the water [11].
Similar species. Palingenia longicauda. It differs in the shape of the elongation of mandibula, which in Ephoron virgo is wedge-like, drawn out forward.
Negative factors. Pollution of the Bulgarian Danube tributaries and of the Danube with domestic and industrial waste waters. The extraction of inert materials from the bottoms of rivers.
Conservation measures taken. None.
References. 1. Russev, 1957; 2. Russev et al., 1984; 3. Russev et al., 1991; 4. Russev et al., 1994; 5. Russev & Uzunov, 1991a; 6. Janeva, 1991; 7. Janeva & Russev, 1989; 8. Janeva & Russev, 1985; 9. Schleuter et al., 1989; 10. Greve et al., 1999; 11. Kureck, 1996.
Author: Yanka Vidinova
