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At least 577 records · Page 32Linked to original sources
PubMed1998

A new species of the Simulium damnosum complex from Uganda, and comparative morphology of the tarsal claws in females of this complex.

The female, male, pupa and larva of Simulium (Edwardsellum) pandanophilum sp. nov. (Diptera: Simuliidae) from western Uganda are described. Diagnostic features are the shape of the tarsal claws of females and, cytogenetically, new intraspecific inversions on chromosomes I and II. Simulium pandanophilum is assigned to the Simulium damnosum complex. Different tarsal claw shapes of West African members of the S. damnosum complex are also described.

Animals↗
PubMed1998

Sibling species distributions of the Simulium damnosum complex in the west African Onchocerciasis Control Programme area during the decade 1984-93, following intensive larviciding since 1974.

During the decade from 1984 to 1993, nine species of the Simulium damnosum complex of blackflies (Diptera: Simuliidae) were identified from the area covered by the Onchocerciasis Control Programme. These were S. damnosum s.s., S. dieguerense, S. konkourense, S. leonense, S. sanctipauli, S. sirbanum, S. soubrense, S. squamosum, and S. yahense. Some of these species were found to consist of two chromosomal variant populations. These were S. konkourense 'Konkouré' and 'Menankaya' forms, S. sanctipauli sensu stricto and 'Djodji' form, S. soubrense 'Chute Milo' and 'Beffa' forms. The distribution of these twelve cytological taxa was assessed in relation to the two main vegetation zones of West Africa (forest and savanna), topography, river size and other factors. The range of each species was influenced by seasonal climatic changes in wind movement and river water level. The most widely distributed species were S. sirbanum and S. damnosum s.s., associated with savanna areas, recorded from all river basins. Simulium dieguerense was restricted mainly to Western Mali on the Rivers Bafing and Bakoye in the Senegal River basin. Simulium squamosum was identified from rivers draining mountainous areas in both the forest and savanna zones. Simulium yahense was found in small permanent rivers along a wide forested band parallel to the coast and was absent from the plains of Togo and Benin. Members of the S. sanctipauli subcomplex had restricted distributions except for S. sanctipauli s.s., which was widespread in large rivers of the forest zone from Sierra Leone to the Volta Lake in Ghana. Simulium soubrense 'Beffa' form occurred in Togo and Benin, S. soubrense 'Chutes Milo' form in Guinea, both 'Konkouré' and 'Menankaya' forms of S. konkourense occurred predominantly in Guinea and S. leonense in Sierra Leone. The relevance of the distribution maps and the importance of the data bank to vector control larvicidal operations are discussed.

Africa, Western↗
PubMed1999

Distribution of the Simulium metallicum complex in Mexico in relation to selected environmental variables.

Larvae of the Simulium metallicum complex (Diptera: Simuliidae) were collected from three foci of human onchocerciasis in Mexico. Specimens were separated into five different cytotypes, identified by morphological characteristics (head pattern and body colour) or polytene chromosome features. Differences were found between foci in the cytotype composition of the S. metallicum complex. Nearly all specimens were cytotype A in the Chamula (97%) and Soconusco (86%) foci. In the Oaxaca focus, however, cytotype I predominated (63%) with 14% cytotype A. Cytotype I comprised only 6% of specimens in the Soconusco focus and was very rare in the Chamula focus. Cytotypes B and H occurred only rarely in all three foci. Cytotype X was found only in Oaxaca. Environmental variables were measured at the collection sites and canonical correspondence analysis (CCA) was used to investigate the associations of cytotype distributions with the following factors: stream size, amount of shade, water clarity, pH, temperature and altitude. Members of the S. metallicum species complex were found to be differentially distributed according to stream conditions and there was a significant correlation between their distributions and the environmental variables. The most important factor in canonical axis 1 of the CCA was pH (t-value -4.38) with temperature (-2.48) and altitude (2.19) having some influence, but the other variables were unimportant. In the second canonical axis, pH (-3.52) was the only variable having a significant effect. Thus, cytotype A was associated with high pH, high temperature and low altitude; B was associated with similar sites but with higher temperatures and at lower average elevations. Cytotype H was found at the centres of the ranges of these variables, I at sites with the lowest temperatures and highest altitudes and X in rivers with the lowest pH.

Animals↗
PubMed1999

Identification of bloodmeals in haematophagous Diptera by cytochrome B heteroduplex analysis.

We developed a DNA assay for bloodmeal identification in haematophagous insects. Specific host cytochrome B gene sequences were amplified by PCR and classified on the basis of their mobility in a heteroduplex assay. In the blackfly Simulium damnosum s.l. (Diptera: Simuliidae), human cytochrome B DNA sequences were identifiable up to 3 days following ingestion of the bloodmeal. In the tsetse Glossina palpalis (Diptera: Glossinidae) collected from tsetse traps in Ivory Coast, bloodmeals were identified as taken from domestic pigs on the basis of their heteroduplex pattern and DNA sequence. Evidently the cytochrome B sequence shows sufficient interspecific variation to distinguish between mammalian host samples, while exhibiting minimal intraspecific variation. The stability of DNA in bloodmeals, for several days post-ingestion by haematophagous insects, allows PCR-HDA assays to be used reliably for host identification.

Animals↗
PubMed2000

Phosphoglucomutase and trehalase isoenzymes of Venezuelan simulium vectors of Onchocerca volvulus.

Phosphoglucomutase (PGM) and trehalase (Tre) isoenzymes of five species of Simulium blackflies (Diptera: Simuliidae), vectors of onchocerciasis in Venezuela, were investigated by means of a portable electrophoresis field kit. Tre differed between S. incrustatum and S. oyapockense s.l. Electrophoretic variation of Tre in other members of the S. amazonicum and S. incrustatum groups merit further investigation. PGM appears to be more useful for separating populations within species complexes. Multiple populations and/or seasonal changes in population structure of S. guianense s.l., S. exiguum s.l. and S. metallicum s.l. were inferred from elecrophoretic variation of PGM.

Animals↗
PubMed2000

Dispersal range of Simulium neavei in an onchocerciasis focus of western Uganda.

The dispersal range of the vector Simulium neavei Roubaud (Diptera: Simuliidae) was investigated in an onchocerciasis focus in Kabarole district, western Uganda, adjacent to the Itwara Forest Reserve, where the species breeds in phoretic association with the river crab Potamonautes aloysiisabaudiae (Nobili) (Decapoda: Potamonautidae). Biting rates were highest at the edge of the forest, but blood-seeking flies were collected up to a distance of about 4 km from the forest. Entomological data did not agree with the geographical distribution of onchocerciasis, which is hyperendemic in larger distances from the forest. The possible reasons are discussed.

Animals↗
PubMed2000

DNA in situ hybridization on polytene chromosomes of Simulium sanctipauli at loci relevant to insecticide resistance.

A DNA technique for in situ hybridization developed by Kumar & Collins (1994) for use on polytene chromosomes of adult Anopheles mosquitoes (Diptera: Culicidae) was modified for use with Simulium larval salivary gland chromosomes (Diptera: Simuliidae). Cloned fragments of several Simulium genes (coding for aspartate amino transferase, cytochrome P450 and DNA polymerase) were successfully mapped physically by assigning specific band locations in Simulim sanctipauli V. & D. This represents the first attempt at locating genes beyond the resolution of linkage to inversions in any blackfly species.

Animals↗
PubMed2000

An epizootic of patent iridescent virus disease in multiple species of blackflies in Chiapas, Mexico.

Simulium blackfly larvae (Diptera: Simuliidae) were collected from rivers and streams at 500-1500 m a.s.l. in Chiapas State of southern Mexico. Among 45 sites surveyed over an area of 2300 km2 (around 15 degrees 15'N 92 degrees 20'W), some Simulium larvae from three sites were opalescent violet-blue, interpreted as patent infection with invertebrate iridescent virus (IIV). Dissection confirmed the presence of putative Iridovirus particles, 130nm diameter, but no IIV isolates were obtained from homogenates injected into Galleria mellonella (L) larvae (Lepidoptera: Pyralidae). All Simulium with patent IIV infection died before metamorphosis, whereas approximately 60% of asymptomatic Simulium survived to adulthood in the laboratory. During 1997, standard monthly samples from two parallel rivers 42-50 km north-west of Tapachula comprised the following species proportions (and rates of patent IIV infection): 41.8% (47%) Simulium mexicanum Bellardi complex, 31.3% (31.4%) S. rubicundum Knab, 10.1% (13.1%) S. paynei, 6.5% (2.9%) S. callidum (Dyar & Shannon), 6.3% (5.1%) S. ochraceum Walker complex, 3.1% (0.7%) S. downsi Vargas et al., 0.7% S. samboni Jennings and 0.2% S. metallicum Bellardi complex, showing a strong correlation between blackfly abundance and the prevalence of patent infection. An epizootic of IIV in January and February (infection rates 41-100%) was followed by absence of larvae (March-August) until the end of the rainy season, when numbers collected on nylon strings rose to approximately 1/cm with patent IIV infection rates of 0-12.5% during September-December. Further investigations are underway to isolate this IIV and assess its potential usefulness for biological control of Simulium pests and vectors of onchocerciasis.

Animals↗
PubMed2002

Assessment of rDNA IGS as a molecular marker in the Simulium damnosum complex.

For five cytospecies of the Simulium damnosum Theobald complex of blackflies (Diptera: Simuliidae) from West Africa, both ends of the intergenic spacer region (IGS) of the rDNA have been sequenced with the aim of developing specific molecular markers. No specific differences in these two regions were detected between Simulium sanctipauli V. & D., Simulium sirbanum V. & D., Simulium soubrense V. & D., Simulium squamosum Enderlein and Simulium yahense V. & D., except in the number of A subrepeats at the 5' end of the IGS (two in S. squamosum and four or five in the others) and in position 310 of the 3' end (a C in S. squamosum and a G in the others). However, genetic distances within and between species overlapped. These DNA sequences had no strong phylogenetic signal, and the trees obtained were mostly unresolved. Although most sequences from S. squamosum clustered together, a few of them were more similar to those in other cytospecies. These results could be explained either by hybridization with genetic introgression or by ancestral polymorphism and recent speciation.

Africa, Western↗
PubMed2003

Mechanisms of resistance to DDT and pyrethroids in Patagonian populations of Simulium blackflies.

Mixed populations of the pest blackflies Simulium bonaerense Coscarón & Wygodzinsky, S. wolffhuegeli (Enderlein) and S. nigristrigatum Wygodzinsky & Coscarón (Diptera: Simuliidae) are highly resistant to DDT and pyrethroids in the Neuquén Valley, a fruit-growing area of northern Patagonia, Argentina. As these insecticides have not been used for blackfly control, resistance is attributed to exposure to agricultural insecticides. Pre-treatment with the synergist piperonyl butoxide (PBO) reduced both DDT and fenvalerate resistance, indicating that resistance was partly due to monooxygenase inhibition. Pre-treatment with the synergist tribufos to inhibit esterases slightly increased fenvalerate toxicity in the resistant population. Even so, biochemical studies indicated almost three-fold higher esterase activity in the resistant population, compared to the susceptible. Starch gel electrophoresis confirmed higher frequency and staining intensity of esterase electromorphs in the resistant population. Incomplete synergism against metabolic resistance indicates additional involvement of a non-metabolic resistance mechanism, such as target site insensitivity, assumed to be kdr-like in this case. Glutathione S-transferase activities were low and inconsistent, indicating no role in Simulium resistance. Knowing these spectra of insecticide activity and resistance mechanisms facilitates the choice of more effective products for Simulium control and permits better coordination with agrochemical operations.

Animals↗
PubMed2004

Vertebrate host specificity of wild-caught blackflies revealed by mitochondrial DNA in blood.

Blood-feeding blackflies (Diptera: Simuliidae) transmit pathogens, harass vertebrate hosts and may cause lethal injuries in attacked victims, but with traditional methods it has proved difficult to identify their hosts. By matching mitochondrial DNA (mtDNA) sequences in blood collected from engorged blackflies with stored sequences in the GenBank database, relationships between 17 blackfly species and 25 species of vertebrate hosts were revealed. Our results demonstrate a predominance of large hosts and marked discrimination between blackflies using either avian or mammalian hosts. Such information is of vital interest in studies of disease transmission, coevolutionary relationships, population ecology and wildlife management.

Animals↗
PubMed2002

Phylogenetic analysis identifies the invertebrate pathogen Helicosporidium sp. as a green alga (Chlorophyta).

Historically, the invertebrate pathogens of the genus Helicosporidium were considered to be either protozoa or fungi, but the taxonomic position of this group has not been considered since 1931. Recently, a Helicosporidium sp., isolated from the blackfly Simulium jonesi Stone & Snoddy (Diptera: Simuliidae), has been amplified in the heterologous host Helicoverpa zea. Genomic DNA has been extracted from gradient-purified cysts. The 185, 28S and 5.8S regions of the Helicosporidium rDNA, as well as partial sequences of the actin and beta-tubulin genes, were amplified by PCR and sequenced. Comparative analysis of these nucleotide sequences was performed using neighbour-joining and maximum-parsimony methods. All inferred phylogenetic trees placed Helicosporidium sp. among the green algae (Chlorophyta), and this association was supported by bootstrap and parsimony jackknife values. Phylogenetic analysis focused on the green algae depicted Helicosporidium sp. as a close relative of Prototheca wickerhamii and Prototheca zopfii (Chlorophyta, Trebouxiophyceae), two achlorophylous, pathogenic green algae. On the basis of this phylogenetic analysis, Helicosporidium sp. is clearly neither a protist nor a fungus, but appears to be the first described algal invertebrate pathogen. These conclusions lead us to propose the transfer of the genus Helicosporidium to Chlorophyta, Trebouxiophyceae.

Actins↗
PubMed2004

Efficiency of Simulium sanctipauli as a vector of Onchocerca volvulus in the forest zone of Ghana.

The role of Simulium sanctipauli Vajime & Dunbar (Diptera: Simuliidae) as a vector of Onchocerca volvulus (Leuckart) (Spirurida: Onchocercidae) in the forest zone of central Ghana was studied in the Upper Denkyira district, where onchocerciasis is hyperendemic. Simulium sanctipauli was found to be a highly efficient vector, with a mean of 377 infective (L3) larvae in the heads of 1000 parous and 122 in the heads of 1000 biting flies. The overall infection rate of 44% of the parous flies with L1, L2 and L3 stages of O. volvulus (identity confirmed by polymerase chain reaction) demonstrates marked anthropophily. Female flies dispersed over a wide area and can transmit onchocerciasis up to at least 10 km away from their breeding sites. Annual community-directed treatments with ivermectin did not have a noticeable effect on the infection rates and parasitic loads of fly populations, which were as high 2 months after as 3 months before the distribution of ivermectin. This failure can be attributed to poor coverage, with treatment taken by only 24.4% of the population of the six study villages.

Animals↗
PubMed2004

A new cytotype of Simulium squamosum from south-west Cameroon.

A new cytotype of Simulium squamosum Enderlein (Diptera: Simuliidae) (here named S. squamosum'D') is described from around Mount Cameroon in south-west Cameroon on the basis of sex-chromosome differences on the short arm of chromosome I. Two polymorphic inversions, IS-To (a new inversion) and IS-2, are partially Y linked. These inversions usually occur together, although IS-To has a higher frequency and is more strongly Y linked than IS-2. This sex-chromosome system has not been previously described and the occurrence and evolution of sex-chromosome systems in S. squamosum is discussed.

Animals↗
PubMed1988

Factors influencing silhouette trap captures of the blackfly Austrosimulium bancrofti in Queensland, Australia.

Three silhouette traps of novel design were used to investigate the trap finding ability of female Austrosimulium bancrofti (Taylor) (Diptera: Simuliidae) in southeast Queensland. The traps were 'upright', 'elongate' or 'square' in shape. Five highly significant factors: hour after sunrise, temperature, relative humidity, trap shape and distance between traps, were included in a model which generated fitted estimates of flies captured under defined conditions. The rate of increase and the level of maximum capture rate indicated that the elongate trap captured the highest numbers of blackflies. An interaction between hour after sunrise and temperature suggests a strong endogenous modification of trap finding activity. Numbers captured increased with increasing distance between traps and decreasing relative humidity. The importance of these results in understanding behaviour of A. bancrofti is discussed.

Animals↗
PubMed1992

Identification of members of the Simulium ochraceum species complex in the three onchocerciasis foci in Mexico.

Larval collections of Simulium ochraceum Walker (Diptera: Simuliidae) were made in a variety of streams in the three onchocerciasis foci in Mexico and identified by cytotaxonomic criteria, based on the banding pattern of polytene chromosomes in larval salivary gland nucleii. S. ochraceum cytotype A was found in the Soconusco focus, cytotype B in the Oaxaca focus and cytotype C (not previously recorded in Mexico) in the Chamula focus. Attempts to analyse chromosomes of adult specimens were unsuccessful. A preliminary study of the cuticular hydrocarbons of adult specimens by gas liquid chromatography provided evidence that this technique may be suitable for separating the cytotypes.

Animals↗
PubMed1994

Aggregated oviposition in the Simulium damnosum complex is mediated by eggs in a laboratory bioassay.

The phenomenon of aggregated oviposition in blackflies (Diptera: Simuliidae) was investigated under controlled laboratory conditions, using wild-caught females of the Simulium damnosum complex in Sierra Leone. A method was developed for inducing Simulium females to lay eggs, and used as a bioassay to measure the responses of gravid S. damnosum s.l. to freshly laid eggs of the same species complex. In a series of two-choice tests, significantly more ovipositing flies chose substrates already containing eggs over control substrates (P = 0.004). The time from introduction of flies into the oviposition system to the onset of egg-laying was significantly less when eggs were already present (P = 0.049). Flies responded more quickly when more eggs were present and the relationship between egg-batch number and the time of this response was curvilinear (P = 0.012). Ecological advantages and disadvantages of such aggregation behaviour and the possible role of semiochemicals in its mediation are discussed.

Animals↗
PubMed1995

Age determination in the blackfly Simulium woodi, a vector of onchocerciasis in Tanzania.

Age-dependent changes in the ovarioles of Simulium woodi (Diptera: Simuliidae) and the age structure of a wild population of this species in the Amani hills of north-eastern Tanzania were studied using the ovarian oil injection technique. Contrary to previous theories, egg sacs degenerate completely and do not form dilatations. The physiological age of the females could be determined only by gonotrophic dilatations formed from degenerating follicles during gonotrophic cycles. In individual females, the proportions of ovarioles with degenerating follicles were 3-54% (mean 22%) in the first cycle and 8-61% (mean 36%) in the second gonotrophic cycle. Agonotrophic degenerating follicles occurred in 2% of ovarioles in 12% of females. Additional information with regard to the degree of parity is given by the level of granulation in the basal body of each ovariole, a group of six to eight cells in the calyx wall enclosed by the end of the ovariolar sheath. Their granulation progressively increased in intensity following each subsequent ovulation.

Aging↗