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The value of the larval head pattern for differentiating Simulium exiguum s.l. and S. gonzalezi (Diptera: Simuliidae) in the onchocerciasis focus of Ecuador

Published online by Cambridge University Press:  10 July 2009

M. Charalambous ,
C. A. Lowry ,
S. Lowell ,
A. J. Shelley  and
M. Arzube
M. Charalambous
Affiliation:
Medical and Veterinary Division, Department of Entomology*, The Natural History Museum, Cromwell Road, London SW7 5DB, UK:
C. A. Lowry
Affiliation:
Medical and Veterinary Division, Department of Entomology*, The Natural History Museum, Cromwell Road, London SW7 5DB, UK:
S. Lowell
Affiliation:
Medical and Veterinary Division, Department of Entomology*, The Natural History Museum, Cromwell Road, London SW7 5DB, UK:
A. J. Shelley
Affiliation:
Medical and Veterinary Division, Department of Entomology*, The Natural History Museum, Cromwell Road, London SW7 5DB, UK:
M. Arzube
Affiliation:
Instituto Nacional de Higiene y Medicina Tropical, “Leopoldo Izquieta Pérez”, Guayaquil, Ecuador
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Abstract

In the Esmeraldas focus of onchocerciasis in Ecuador, the larvae of the primary vector Simulium exiguum Roubaud are found in sympatry with the non-vector S. gonzalezi Vargas & Díaz Nájera. Distinguishing the pre-ultimate stage larvae of these two species usually relies on the pattern of markings on the cephalic apotome. These patterns appear either as dark spots against a pale cuticle (positive head pattern) or as pale spots within a darkened area of the cuticle (negative head pattern). Larvae of S. exiguum s.l. usually exhibit positive or no head patterns whilst those of S. gonzalezi usually have negative head patterns. The purpose of this paper was to investigate head pattern variation (scored in one of six categories) in (polytene) chromosomally identified larvae of the two species and cytotypes of S. exiguum from three collection sites in Ecuador (including one in the onchocerciasis focus). The head patterns of a total of 1183 larvae were studied. Chromosomal identification of penultimate instar larvae revealed only the presence of the Cayapa and Quevedo cytotypes of S. exiguum (n=208). Both cytotypes exhibited a wide range of head patterns from positive to negative. The results indicate that negative head patterns cannot be used to reliably distinguish between larvae of S. exiguum s.l. and S. gonzalezi. All except one larva with negative head patterns were females (n=53), suggesting that head pattern in this species complex might be a sex-linked character.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 87 , Issue 1 , February 1997 , pp. 19 - 24
Copyright
Copyright © Cambridge University Press 1997

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References

Charalambous, M., Ready, P.D., Shelley, A.J.Arzube, M. & Lowry, C.A. (1993a) Cytological and isoenzyme analysis of the Bucay and Quevedo cytotypes of the onchocerciasis vector Simulium exiguum (Diptera: Simuliidae) in Ecuador. Memorias do Instituto Oswaldo Cruz 88, 39–48.CrossRefGoogle ScholarPubMed
Charalambous, M., Shelley, A.J. & Arzube, M. (1993b) Distribution and taxonomic status of chromosomal forms of the onchocerciasis vector Simulium exiguum in central Ecuador. Medical and Veterinary Entomology 8, 299–303.Google Scholar
Conn, J., Rothfels, K.H., Procunier, W.S. & Hirai, H. (1989) The Simulium metallicum complex (Diptera: Simulidae) in Latin America: a cytological study. Canadian Journal of Zoology 67, 1217–1245.CrossRefGoogle Scholar
Coscarón, S. (1991) Fauna de agua dulce de la Republica Argentina. Insecta Diptera (Fasciculo 2 Simuliidae) 38, 5–304 [+ unnumbered figure pages].Google Scholar
Crosskey, R.W. (1960) A taxnomic study of the larvae of West African Simuliidae (Diptera: Nematocerca) with comments on the morphology of the larval black-fly head. Bulletin of the British Museum (Natural History) (Entomology) 10, 1–74.CrossRefGoogle Scholar
Golini, V.I. & Rothfels, K. (1984) The polytene chromosomes of North American blackflies in the Eusimulium canonicolum group (Diptera: Simuliidae). Canadian Journal of Zoology 62, 2097–2109.Google Scholar
Kelly, J.E. (1993) Morphological analysis of the Quevedo and Cayapa cytotypes of the Simulium exiguum complex in Ecuador. 42 pp. Unpublished Msc thesis. London School of Hygiene and Tropical Medicine, University of London.Google Scholar
Millest, A.L. (1990) Differences in the larval head patterns and body coloration of members of the Simulium metallicum species complex (Diptera: Simuliidae) from Mexico. Bulletin of Entomological Research 80, 191–194.CrossRefGoogle Scholar
Moulton, J.K. & Adler, P.H. (1995) Revision of the Simulium jenningsi species-group (Diptera: Simuliidae). Transactions of the American Entomological Society 121, 1–57.Google Scholar
Okazawa, T. & Onishi, O. (1980) Description of a new species of Simulium (Simulium) Latreille and redescription of Simulium (Simulium) metallicum Bellardi from Guatemala (Diptera: Simuliidae). Japanese Journal of Sanitary Zoology 31, 167–179.Google Scholar
Procunier, W.S., Shelley, A.J. & Arzube, M. (1985) Sibling species of Simulium exiguum: the primary vector of onchocerciasis in Ecuador. Revista Ecuatoriana de Higiene y Medicina Tropical 35, 49–59.Google Scholar
Sawyer, J. (1991) A comparision of taxonomic techniques in the identification of sibling species of South American Simuliidae. 216 pp. Unpublished PhD thesis. University of Salford, UK.Google Scholar
Shelley, A.J. & Arzube, M. (1985) Studies on the biology of Simuliidae (Diptera) at the Santiago onchocerciasis focus in Ecuador, with special reference to the vectors and disease transmission. Transactions of the Royal Society of Tropical Medicine and Hygiene 79, 328–338.CrossRefGoogle Scholar
Shelley, A.J., & Arzube, M. & Couch, C.A. (1989) The Simuliidae (Diptera) of the Santiago onchocerciasis focus of Ecuador. Bulletin of the British Musuem (Natural History) (Entomology) 58, 79–130.Google Scholar