Sympatric occurrence of forest and savannah morphotypes of Simulium damnosum complex (Diptera: Simuliidae) in Osun State, Nigeria

Abstract

Simulium damnosum Theobald complex is a group of black flies which vector filarial worms that cause onchocerciasis in Africa. Studies were conducted to investigate the morphological composition of adult S. damnosum complex in three ecological zones of Osun State, Nigeria. Adult black flies were sampled between October 2014 and September 2016, and the wing tufts, antennae, fore coxae and other morphotaxonomic characters were observed and classified following standard methods. The results revealed a sympatric occurrence of both forest- and savannah-dwelling groups (morphotypes) of black flies at each zone with the Guinea savannah zone (Iwo) having significantly higher abundance of forest than savannah black flies. The derived savannah (Ede) had higher abundance of savannah than forest black flies while the rainforest (Obokun) had more forest than savannah black flies but there was no significant difference between them. In Iwo, the highest abundance of forest flies was obtained in October and June while savannah flies were highest in November. The monthly abundance of each morphotype of black flies was significantly different in Ede but not in Obokun. Wing tuft colours among forest flies varied significantly in Iwo and Ede. This study indicates that there is substantial morphological diversity among sibling species of black flies which is useful for identification and could be exploited in black fly control. The presence of savannah flies in the three zones calls for surveillance for potential incursion of blinding parasite strain which migrant savannah flies could introduce to the communities.