Identification of members of the Simulium ochraceum species complex in the three onchocerciasis foci in Mexico

Larval collections of Simulium ochraceum Walker (Diptera: Simuliidae) were made in a variety of streams in the three onchocerciasis foci in Mexico and identified by cytotaxonomic criteria, based on the banding pattern of polytene chromosomes in larval salivary gland nucleii. S. ochraceum cytotype A was found in the Soconusco focus, cytotype B in the Oaxaca focus and cytotype C (not previously recorded in Mexico) in the Chamula focus. Attempts to analyse chromosomes of adult specimens were unsuccessful. A preliminary study of the cuticular hydrocarbons of adult specimens by gas liquid chromatography provided evidence that this technique may be suitable for separating the cytotypes.