Biology of snail-killing flies from Africa and southern Spain (Sciomyzidae: Sepedon)

Abstract

Sepedon h. hispanica was collected in freshwater marshes in southern Spain and reared through its entire life-cycle in the laboratory.Larvae of this species differ from those of the twenty-one other reared species of Sepedon in not normally invading water, feeding as parasitoids throughout the first half of larval life (that is, permitting their food snails to live for several days), and in restricting their diet to the genus Succinea during that time.Each newly hatched larva of S. h. hispanica crawls between the mantle and foot of a living Succinea elegans, S. pfeifferi or S. putris and remains there while developing into or completely through the second larval instar.After the death of the first food snail the larva becomes predatory and loses its host specificity. Then it attacks a wide range of pulmonate snails, kills each victim quickly, and destroys a series of individuals belonging to species of Succinea, Lymnaea and Physa.Adults of S. ruficeps and S. scapularis were reared from larvae and pupae collected in Ethiopia.The larvae of both African species are aquatic predators which kill and consume various pulmonate snails unselectively. They are equivalent ecologically to all other larvae of Sepedon previously described.The egg, three larval instars, and puparium of S. h. hispanica, and the mature larvae and puparia of S. ruficeps and S. scapularis, are described and figured.A key is presented to immature stages of the Palaearctic species of Sepedon.We wish to thank Dr W. C. Frohne, Alaska Methodist University, Anchorage, Alaska for collecting and rearing Sepedon ruficeps and S. scapularis. Dr E. Morales Agacino, Instituto Espanol de Entomologia, Madrid; Dr M. Mendizabol, Dr J. Verdejo and D. J. Paris Lopez, Instituto de Acclimatacion, Almeria; and Professor Dr I. Docavo Alberti and Dr B. Llopis Minguez, University of Valencia, aided during the senior author's field-work in Spain. We thank Dr J. Verbeke, Institut royal des Sciences naturelles de Belgique, for determinations and distributional data; Mr L. W. Stratton, Harpenden, England, and Dr H. J. Walter, Dayton, Ohio, Museum of Natural History, for determinations of Gastropoda; and Mrs L. Lyneborg, Zoological Museum, Copenhagen, for Fig. 25.