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Simulium guianense Wise is a Latin American vector complex of black flies associated with transmission of the causal agent of human onchocerciasis (river blindness). An analysis of the chromosomal banding patterns of 607 larvae of S. guianense s. l. revealed a high level of variation involving 83 macrogenomic rearrangements across 25 populations in Brazil, French Guiana, and Venezuela. The 25 populations were assigned to 13 cytoforms (A1, A2, B1–B4, C, D, E1–E4, and F), some of which are probably valid species. Based on geographical proximity, a member of the B group of cytoforms probably represents the name-bearing type specimen of S. guianense and the primary vector in the last-remaining onchocerciasis foci in the Western Hemisphere. Cytoform B3 in Amapá State is implicated as an anthropophilic simuliid in an area currently and historically free of onchocerciasis. Distributions of cytoforms are associated with geography, elevation, and drainage basin, and are largely congruent with ecoregions. Despite extraordinarily large larval populations of S. guianense s. l. in big rivers and consequent production of female flies for dispersal, the cytoforms maintain their chromosomal distinction within individual rivers, suggesting a high degree of fidelity to the specialized breeding habitats—rocky shoals—of the natal rivers. © 2017 Adler et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Simulium guianense Wise (Diptera: Simuliidae) is the main vector of the nematode Onchocerca volvulus (Leuckart) (Spirurida: Onchocercidae), which causes onchocerciasis in the Amazonian focus of the disease. We present the first report of the presence of S. guianense in the Parnaiba River basin, its oviposition behavior, and its number of instars. Immatures were found in high density on bedrock, on leaves of Podostemaceae and other aquatic plants, and on branches and leaves of riparian vegetation. Larvae and pupae were collected in 9 rivers: 8 in the state of Piaui and 1 in the state of Ceara. Six instars were determined for a population in Piaui. Oviposition behavior was of the dabbing type. Ants (Solenopsis sp.; Hymenoptera: Formicidae) preyed on larvae and pupae stranded when the river receded.

Simulium guianense sensu lato es el vector de Onchocerca volvulus en el foco amazónico de oncocercosis, al sur de Venezuela. En esta nota presentamos la primera identificación geográfica, caracterización ecológica y descripción del paisaje del hábitat acuático de las formas pre-adultas de este complejo de especies, en el área de transmisión de esta parasitosis. Las larvas y pupas de esta especie fueron muestreadas sobre plantas Podostemaceas presentes en un raudal de aguas claras (pH= 7, conductividad = 158 umhos/cm, y caudal = 0.12 m³/s) del río Orinoquito, en el área de la Reserva de Biosfera del Alto Orinoco-Casiquiare. El paisaje del área de muestreo correspondió a un bosque húmedo ombrófilo macrotérmico y el raudal del río estudiado fluye sobre una planicie aluvial de sustrato de arena y gravas de cuarzo. El presente hallazgo contribuirá con la estratificación epidemiológica de la endemia y orientará las medidas de eliminación de la oncocercosis al sur de Venezuela. Simulium guianense sensu lato is the main vector of Onchocerca volvulus in the Amazonian onchocerciasis focus, southern Venezuela. Here, we present the first report of the pre-adult aquatic habitat spatial distribution as well as the landscape and the habitat ecological characterization of this species complex within the endemic area. Larvae and pupae were collected on submerged aquatic plants (Podosteamaceas) located in a waterfall (pH = 7, conductivity = 158 umhos/cm, discharge = 0.12 m3/s) of the Orinoquito river, in the Upper Orinoco-Casiquiare Biosphere Reserve. These results will help with the epidemiological stratification and control program of the onchocerciasis in southern Venezuela.

We describe the hourly patterns of parous biting activity of the three main simuliid vectors of human onchocerciasis in the Amazonian focus straddling between Venezuela and Brazil, namely, Simulium guianense s.l. Wise; S. incrustatum Lutz, and S. oyapockense s.l. Floch and Abonnenc. Time series of the hourly numbers of host-seeking parous flies caught in five Yanomami villages during dry, rainy, and their transition periods from 1995 to 2001 were investigated using harmonic analysis (assuming an underlying circadian rhythm) and periodic correlation (based on Spearman's r). Parous S guianense s.l. showed a bimodal activity pattern, with a minor peak in mid-morning and a major peak at 16:00 h. S. incrustatum exhibited mainly unimodal activity during either early morning or midday according to locality. S. oyapockense s.l. bit humans throughout the day mainly between 10:00 and 16:00 h but also showed bimodal periodicity in some localities. Superimposed on the endogenous, species-specific daily cycles, parous activity showed variation according to locality, season, air temperature and relative humidity, with biting being promoted by warmer and drier hours during wet seasons/periods and reduced during hotter times in dry seasons or transitions. The results are discussed in terms of their implications for blackfly biology and ecology as well as onchocerciasis epidemiology and control.

The objectives of the present study were to broaden the survey of simuliid species in French Guiana and to cytologically analyze the species in the Simulium perflavum species group. Twelve species of Simulium were collected from which S. goeldii, S. quadrifidum, S. trombetense, S. near incrustatum, S. metallicum (s.l.) sp1, S. metallicum (s.l.) sp2 and S. ochraceum (s.l.) are reported for the first time for this region. The only species collected in the S. perflavum group was S. rorotaense; 34 larvae of this species were cytologically analyzed, all of which had the standard sequence. S. metallicum (s.l.), S. ochraceum (s.l.), S. guianense (s.l.) and S. oyapockense (s.l.) are involved with transmission of onchocerciasis in Central and South America, however, in French Guiana these species were not found biting humans during the sampling period. With the few collections made during this study, we increase the number of simulid species known in French Guiana from 6 to 13. It is clear that more simuliid species can be expected to be found when more sampling is done, including collections in other ecoregions in French Guiana.

The male, female, pupa and larva of Simulium litobranchium n. sp. are described and illustrated. This new species has 12 gill filaments, as do S. duodenicornium Pepinelli, Hamada & Trivinho-Strixino, S. guianense Wise, S. hirtipupa Lutz, S. perplexum Shelley, Maia-Herzog, Lunas Dias & Couch and S. scutistriatum Lutz, but it can be distinguished from these other species by a combination of characters observed at the pupal and adult stages. DNA barcoding showed that Simulium litobranchium n. sp. exhibits more than 4% nucleotide divergence in cytochrome oxidase I from three other closely related species in the Neotropical subgenus S. (Thyrsopelma). The new species was collected in the Brazilian states of Goiás and Minas Gerais and inhabits rivers 30–40 m in width in the Paraná River hydrographic basin. Females were not observed engaging in anthropophilic behavior.

Experimental and natural infections with Onchocerca volvulus were studied in several anthropophilic blackfly species present in the endemic area of the Upper Orinoco region of Venezuela. When fed on four different Yanomami volunteers in the Sierra Parima, the total infection rate was 31.4% for Simulium guianense in comparison with 7.5% for S. limbatum. The proportion of ingested microfilariae that entered the thorax during the first 24 hours and completed development to the infective stage was also much lower in the latter than in the former species. There was no larval development of O. volvulus in S. antillarum, but one female harboured in its head six infective larvae of a zoonotic filaria. When S. oyapokense s.l. was fed on an infected volunteer in the Upper Orinoco most flies ingested few microfilariae, and further development reached only the L1 stage. Natural infection and infectivity rates for S. guianense in two localities of the Sierra Parima were 0.2-4.0% and 1.3-10.2%, respectively, more than 50% of the L3 larvae being in the head. The corresponding data for S. oyapockense s.l. in the Upper Orinoco were 0.1-0.5%, although the only L3 larva found did not correspond to O. volvulus. It is suggested that S. guianense is the main vector of onchocerciasis in the Sierra Parima and that S. limbatum could play a secondary role. Simulium oyapockense s.l. replaces them in the Upper Orinoco and may maintain a degree of transmission, but its epidemiological importance remains to be assessed.

Simulium perplexum, new species, is described from the male, female and pupa and compared with the closely related S. guianense Wise. The distribution and biology of the new species are discussed. The confusion between S. perpelxum and S. guianense has hitherto prevented accurate identification of the primary vector of human onchocerciasis in highling, hyperendemic areas of the Amazônia focus of Brazil and southern Venezuela. Macho, fêmea e pupa de Simulium perplesum sp. n. são comparados com sua espécie próxima S. guianense Wise. Discutimos sua biologia e distribuição. A identidade incerta de S. guianense impedia a correta identificação do vetor primário da oncocercose humana nas áreas elevadas e hiperendêmicas do foco amazônico brasileiro e venezuelano.