Identification of larval and adult Simulium yahense and Simulium sanctipauli based on species-specific enzyme markers and their distribution at different breeding habitats in Central Liberia.

Human-biting adults and late instar larvae of the Simulium damnosum complex from four ecologically different simuliid breeding habitats in the Firestone Rubber Plantation at Harbel, Liberia, were identified morphologically and the monthly species composition of each site was recorded. Samples of the predominant species found at each site were assayed electrophoretically for species-specific variants of phosphoglucomutase (PGM) and trehalase (TRE). Enzyme identifications of flies and larvae were compared with morphological identifications to determine the accuracy of field identifications relying upon morphological characters. Enzyme identifications confirmed the accuracy of over 98% of the adult female identifications. S. yahense was found to be the predominant human-biting species at each site over the 10 months of sampling, with S. sanctipauli comprising a small percentage of the biting fly population. Species-specific larval enzymes confirmed the accuracy of more than 96% of the larval identifications. S. yahense was the predominant larval species found in smaller, more shaded, cooler breeding waters, while S. sanctipauli predominated in the single large watercourse that was sampled. Normally allopatric, mixed populations of these two larval species were found to exist at all sites, but sympatry occurred primarily during the wet season months of May-October. Biting activity of S. sanctipauli was found to be greatest during wet season months, and generally reflected the increase of S. sanctipauli in the larval populations of habitats dominated by S. yahense. The low human-biting activity of S. sanctipauli at all sites and during times which fostered large populations of S. sanctipauli larvae may be an indication of this specie's zoophilic tendency. Circumstantial evidence of hybridization, the expression of PGM and TRE species-specific variants for both species, was found in adults and larvae morphologically identified as S. yahense. The frequency of this "hybrid" condition, based upon PGM and TRE, was calculated to be comparable to the frequency of hybridization as determined by larval chromosome inversions.