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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 91, Num. 6, 1996
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Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 91(6),
Nov./Dec. 1996,
RESEARCH NOTE
The Need for an Integrated Approach to the Taxonomy of
Neotropical Simuliidae, with Special Reference to Larval
Colour
S Luz/+, AJ Shelley, M Maia-Herzog*
Department of Entomology, British Museum (Natural History),
Cromwell Road, London, SW7 5BD, U.K. *Departamento de
Entomologia, Instituto Oswaldo Cruz, 21045-900 Rio de Janeiro,
RJ, Brasil
+Corresponding author. Fax: +55-21-290.9339
Received 5 February 1996, Accepted 15 July 1996
Key words: Neotropical Simuliidae - taxonomy- morphology-
cytology
Code Number: OC96130
Sizes of Files:
Text: 6.0K
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The taxonomy and identification of Simuliidae, a medically
important family of Diptera with a worldwide distribution, is
largely based on the morphology of adult flies and their pupae
and larvae. Amongst the major identification characters used
in the identification of morphospecies (species that are able
to be identified on morphological characters) is the
coloration of adults and larvae and this character has been
widely used in both local and regional identification keys in
the Afrotropical region [P Freeman & B de Meillon 1953
Simuliidae of the Ethiopian region, London, British
Museum (Natural History), 74 pp]. A taxonomic study of the
larvae of West African Simuliidae (Diptera: Nematocera) with
comments on the morphology of the larval black-fly head was
developed by RW Crosskey (1960 Bul BMNH Entomol
10: 1-74). In the Neotropical region adult coloration
and larval head patterns were used as important characters (S
Coscaron 1991 Insecta Diptera 2 Simuliidae. Fauna de agua
dulce de la Republica Argentina 304 pp.) and both head
pattern and coloration of larvae were used for species
recognition in the Santiago onchocerciasis focus of Ecuador,
although variations were detected in these characters in some
species (AJ Shelley et al. 1989 Bul BMNH Entomol 58:
79-130).
The examination of polytene chromosomes from the silk glands
of larvae for the identification of cytospecies
(morphologically identical species that are only
distinguishable on chromosomal banding patterns) in complexes
of vectors of onchocerciasis in Latin America has led to more
detailed examination of the morphological characters of
larvae. Using a combination of head pattern and body
coloration in larvae some of the cytotypes of the 12 recorded
for the Simulium metallicum complex, which contains
vector cytotypes of human onchocerciasis in Mexico, Guatemala
and Venezuela, could be distinguished from one another
although geographical variation in these characters was
thought to exist (J Conn et al. 1989 Can J Zool 67:
1217-1245, AL Millest 1990 Bul Entomol Res 80:
191-194).
The head pattern character had previously been used in the
Santiago onchocerciasis focus of Ecu-ador to distinguish
larvae of the S. exiguum complex, the primary vector of
the disease there, from the sympatric non vector species S.
gonzalezi. Shelley et al. (loc. cit.) found that
S. gonzalezi always had a negative head pattern (dark
areas with pale spots on cephalic apotome) while in the S.
exiguum complex this condition was rare, the normal
pattern being positive (dark spots on cephalic apotome). In
order to further test the validity of this interspecific
character samples of the S. exiguum complex from
localities both within and outside the onchocerciasis focus
were cytotyped and scored for head pattern (M Charalambous et
al. 1996 Bul Entomol Res in press). Variations from
positive to negative were found in the Cayapa and Quevedo
cytotypes of S. exiguum to a varying degree in each
locality, thereby negating head spot pattern as the main
character for separating S. exiguum from S.
gonzalezi. This would be of major significance in any
future control campaign using larvicides since it will be
impossible to accurately determine species distribution and
target only the vector S. exiguum.
Integrated morphological and cytological studies on S.
exiguum cytotypes in Ecuador also revealed that the
character of larval colour varied in the Aguarico cytotype. In
this form a sex-linked colour dimorphism (green and brown) was
observed. Similar variations of brown, green, blue or pink
bands have been observed in the primary lowland vector species
complex S. guianense in the Amazonia focus of Brazil
and preliminary indications are that one of the colours may be
sex linked and that coloration is probably not cytotype
specific (M Charalambous et al. 1996 Med Vet Entomol in
press).
An integrated study of the primary vectors of onchocerciasis
in lowland areas of the Amazonia focus of Brazil, S.
roraimense and the S. oyapockense complex, has
provided preliminary evidence for the failure of colour
variation as a sound interspecific morphological character. In
these species, which both only have a positive head pattern,
colour variations include pure white to white with grey, brown
or green bands in both species. Studies continue to assess the
variation in different populations of S. roraimense and
cytotypes of the S. oyapockense species complex, taking
into account the added criterion of larval diet which is
thought to also affect coloration.
In conclusion, it is necessary to obtain large samples of
larvae for both morphotaxonomic and cytotaxonomic studies to
determine whether head pattern and body coloration may be a
locally important interspecific character or not, since they
are now known to be too variable for use over the wide species
range of several vectors of onchocerciasis in Latin America.
Copyright 1996 Fundacao Oswaldo Cruz
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