Reproductive Status of Several Members of the Simulium arcticum Complex (Diptera: Simuliidae) in Three Populations in Central Washington State

Abstract. Black fly larval collection sites at three rivers in central Washington state all possess taxa of the Simulium arcticum Malloch complex with the autosomal inversion, IS-1, in high enough frequency to test for Hardy-Weinberg equilibrium independently at each site. Such tests determine reproductive status of the taxa present. These situations in which the IS-1 autosomal inversion is in relative high frequency are rare. Moreover, earlier molecular comparisons suggest a single taxon for the S. arcticum complex and cytogenetic studies at the local level may or may not support earlier molecular work. Such knowledge could further our understanding of the proper taxonomy of these taxa, that is, whether they are good biological species or not. I scored the three genotypes of the IS-1 inversion in 247 larvae to test the reproductive status of populations of three members of the Simulium arcticum complex (Simulium brevicercum, S. saxosum, and the newly discovered cytotype (S. arcticum IIL- 81) at the Methow, Entiat and Wenatchee rivers of Washington state. In all three cases, larvae conformed to Hardy-Weinberg equilibrium, suggesting these populations were panmictic when the collections were made. Thus, these results support earlier molecular work and indicate that the three taxa at these sites can freely interbreed.