The Simulium and S.Metallicum species complexes in Mexico: identification, distribution and relation to onchocerciasis

Both S.ochraceum and S.metallicum, which are vectors of <br/>onchocerciasis, are now known to be species complexes <br/>(Hirai et in preparation; Conn, 1988). <br/><br/>Larval collections were made in a variety of streams in <br/>the three onchocerciasis foci in Mexico and identified by <br/>cytotaxonomic criteria. S.ochraceum cytotype A was found in <br/>the Soconusco focus, cytotype B in the Oaxaca focus and <br/>cytotype C in the Chamula focus. Cytotype C was recorded in <br/>Mexico for the first time. S.metallicum cytotypes A, B, H <br/>and I were found in all three of the foci. Cytotypes B, H <br/>and I were recorded in Mexico for the first time. In <br/>addition a new cytotype, named X, was discovered in the <br/>Oaxaca focus. Attempts to analyse chromosomes of <br/>S.ochraceum adults were unsuccessful. <br/><br/>The larval head patterns and body colouration of <br/>different cytotypes of S.metallicum were examined and <br/>variations were found between them, Cytotypes A, B, H and I <br/>could be distinguished in the majority of cases on these <br/>morphological differences. Cytotype X however resembled <br/>cytotype B. <br/><br/>Cuticular hydrocarbon analysis by gas liquid <br/>chromatography, a technique to distinguish adult members of <br/>species complexes, was attempted on S.ochraceum and <br/>S.metallicum specimens. Some separation was achieved <br/>amongst S.ochraceum cytotypes A, B and C. <br/><br/>The distributions and abundances of the larvae of <br/>different members of the S.ochraceum and S.metallicum <br/>species complexes and other Simulium species were <br/>investigated in relation to selected environmental <br/>variables, by multivariate analyses. Different cytotypes of <br/>each vector complex were found to be associated with <br/>characteristic stream conditions. <br/><br/>The distribution of the different cytotypes of <br/>S.ochraceum and S.metallicum in relation to onchocerciasis <br/>is discussed.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

1989

Author dc:creator

• Millest, Alice Lucy