Four new cytotypes of the onchocerciasis vector blackfly Simulium guianense in Brazil

Abstract

Simulium (Trichodagmia) guianense is an important Amazonian vector of onchocerciasis. Examination of the polytene chromosome banding patterns of larvae from five sites in Brazil revealed the occurrence of four cytotypes, designated A, B, C and D. The chromosomal standard, Simulium guianense A, occurred at two localities in Goias State (on the Rio Tocantins and Rio Mucambão) where it was the only cytotype. The other three sites examined yielded one different cytotype from each: B from Rio Oyapoque in Amapa State, C from Rio Tocantins in Maranhão State, and D from Rio Xingu in Para State. All cytotypes differed by at least two fixed inversions, but a sex determining system was not evident in any cytotype. As the cytotypes have been found allopatrically it is not certain that they represent sibling species; sampling of sympatric populations would resolve this. During certain times of the year, voracious anthropophagy by S.guianense sensu lato occurs at the localities sampled for cytotypes A, C and D (biting data are not available for the cytotype B locality). In some other areas, however, S.guianense s.l. is entirely zoophilic. Further studies are needed, therefore, to elucidate the biting habits, vectorial capacity, geographic distribution and taxonomic status of these four, and perhaps additional, cytotypes comprising the S.guianense complex.

Isolation by distance and a chromosomal cline in the Cayapa cytospecies of Simulium exiguum, the vector of human onchocerciasis in Ecuador

“…were morphologically identified using the key in Shelley et al (1989). The three giant polytene chromosomes (I, II and III; 2n ¼ 6) of penultimate instar larvae were stained using feulgen and analysed (using methods in Charalambous et al, 1996) to identify the chromosomal forms at each collection site. Only the Cayapa cytospecies and the Bucay and Quevedo cytotypes of the Bucay cytospecies were found.…”

“…In Brazil, the different cytotypes of the vector, S. guianense s.l. occupy different river systems (Charalambous et al, 1996). In Ecuador, the Cayapa cytospecies of S. exiguum is known to have a northerly distribution whilst the more southerly Quevedo and Bucay cytotypes of the Bucay cytospecies are, respectively, parapatric and allopatric with the Cayapa cytospecies (Charalambous et al, 1993b).…”

Cytotaxonomy of Simulium cauchense Floch & Abonnenc and Simulium quadrifidum Lutz (Diptera: Simuliidae) in Brazilian Amazonia

“…In Brazil, numerous black flies have been investigated cytotaxonomically (e.g., Campos et al 1996, Charalambous et al 1996, Hamada & Adler 1999, Luz 1999, Ríos-Velásquez et al 2002, Pereira 2004. While chromosomal studies are often essential in revealing sibling species and resolving relationships, the strongest taxonomic and phylogenetic resolution of black flies comes from a combined chromosomal-morphological approach.…”

Chromosomal comparisons among and within populations of Simulium (Chirostilbia) pertinax (Diptera, Simuliidae)

“…Despite the medical and socio-economic importance of some black fly species in Brazil, few cytological studies have been published (Charalambous et al 1996, Campos et al 1996, Hamada & Adler 1999. The objective of the present study was to compare the banding patterns of larval polytene chromosomes of six Simulium (Chirostilbia) pertinax populations in the absence or presence of selection pressure caused by regular treatment with the larvicide temephos.…”