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Studies on the Life‐history and Breeding of Ecdyonurus venosus (Ephemeroptera)

1939; Zoological Society of London; Volume: B109; Issue: 3-4 Linguagem: Inglês

10.1111/j.1096-3642.1939.tb00722.x

0370-2774

Ruth Rawlinson,

Fish Ecology and Management Studies

I. A brief survey of the British members of the genus Ecdyonurus is given. II. A special study is made of the Ecdyonurus population of the River Alyn, Denbighshire. III. An examination of the presumed specific differences of the nymphs and imagines of E. venosus (Fab.), E. venosus var. queesitor, E. longicauda, and E. forcipula, together with a study of the Alyn Ecdyonurus population, lead to grave doubts concerning the recognition of these flies as true species. Two suggestions are made–either E. venosus (Fab.), the Alyn venosus, E. longicauda, and E. forcipula are local varieties, races, or seasonal forms which will in future be found to grade into one another, or the Alyn Ecdyonurus population is incompletely separated into the species described from elsewhere as distinct. IV. The author regards the Alyn E. venosus as a variety of E. venosus (Fab.) which comes within the possible range of variation in this species. Until the true status of the various forms has been settled, the Alyn E. venosus is referred to throughout as E. venosus to distinguish it from E. venosus (Fab.). V. The life-history of the Alyn form of E. venosus–pairing, oviposition, and the development from the egg to the imago–has been described. There are at least two broods a year. VI. The external features, habitat, and habits of the imagines and nymphs of this form are described. The mode of feeding of the nymphs is also described. VII. A study of weekly samples of the nymphal population during the summer and monthly samples during the winter shows a marked seasonal difference in the rate of nymphal growth and the presence of two definite broods of flies a year. The first swarms appear in June, the second from July to October. The early summer eggs hatch and emerge as flies within two months, whereas the autumn ones grow much more slowly and emerge the following June. VIII. An analysis of the population samples collected between May 1937 and May 1938 is given.