Size and fecundity of adult Simuliidae (Diptera) as a function of stream habitat, year, and parasitism

Abstract

Adult Prosimulium mixtum, Cnephia ornithophilia, and Stegopterna mutata, whose larvae develop during the winter, varied in size and fecundity between streams, within the same stream, and between years. In P. mixtum the greatest variation in the same year between sites was a fivefold difference in the mean fecundity, and between years at the same site a twofold change was observed. Size of males and females of P. mixtum and C. ornithophilia were equally affected by the environment. Effects of mermithid nematodes in the Simulium venustum complex and an ovarian fungus in St. mutata were also investigated. The fungus and one mermithid population did not affect the size of the female flies while the second mermithid population with a different development pattern did decrease the size of the flies. These results are discussed in relation to the ecology and control of Simuliidae.