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PubMed1997

Humans vary in their ability to elicit biting responses from Simulium venustum (Diptera:Simuliidae).

Human subjects were exposed to Simulium venustum (sensu lato) to determine whether biting rates differed among individuals. Tests with S. venustum collected from a CO2-baited target demonstrated that one subject was consistently bitten more often than another. For each individual, biting increased with the differential between skin and ambient temperature. Latex rubber membranes that had been worn against the skin of subjects and then stretched onto a warned aluminum block were always bitten less often than control membranes. Results lend credibility to popular notions that some people are bitten more readily than others and show that biting rates are partially dependent on interindividual variation in skin secretions and skin temperature.

Animals↗
PubMed1997

Black fly (Diptera:Simuliidae) salivary secretions: importance in vector competence and disease.

When blood-feeding, black flies introduce secretions into the feeding lesion that act in a coordinated manner on the 3 arms of the vertebrate hemostatic system (platelet aggregation, coagulation, and vasoconstriction). Apyrase activity inhibits platelet aggregation and is ubiquitous in the saliva of black flies, although activity per gland varies by species and has a positive association with anthropophagy. Anticoagulants target components in the final common pathway of the coagulation cascade, including factors V, Xa, and II (thrombin). The antithrombin salivary protein may exert a redundant effect by inhibiting the role of thrombin in platelet aggregation. Antithrombin presence and activity also varies among black fly species, and exhibits a positive correlation with zoophagy. Vasodilation of capillaries to increase blood supply to the feeding wound appears to be an important requirement for Simulium spp., because substantial erythema-inducing activity, has been demonstrated in salivary glands of all New World species examined. Salivary glands of Simulium ochraceum (Walker), a highly anthropophilic vector of Onchocerca volvulus (Leuckhart), contain greater vasodilator activity than several other species, including S. metallicum Bellardi, a secondary zoophagic vector of human onchocerciasis. Simulium vittatum Zetterstedt saliva affects immune cell responses and cytokine production. The ability of the saliva to modulate components of the host immune system provides an opportunity for enhancing transmission of pathogens during bloodfeeding. Thus, the likely possibility that effective pathogen transmission relies on vector saliva may complement present efforts aimed at target epitopes of O. volvulus or identify additional molecules to be investigated as part of a "river blindness" vaccine cocktail. Components in saliva also may enhance the transmission of other microbial agents either by a cofeeding process similar to that observed in ixodid ticks or through rupture of the labrum during escape of Onchocerca infective stage larvae. In a few instances, saliva of some Simulium spp. also has been associated with extensive tissue and organ pathology, including hemorrhagic shock and death. Pathologic signs associated with this syndrome indicate an enhanced antihemostatic activity in saliva.

Animals↗
PubMed1997

Nectar versus honeydew as sources of sugar for male and female black flies (Diptera: Simuliidae).

Black flies were collected twice daily using a vehicle-mounted insect net on 8 sample days between 20 May and 9 July 1993. The contents of the crops and midguts of 160 male and 160 female Simulium venustum Say were analyzed individually by thin-layer chromatography. Fourteen different combinations were identified of the following sugars: fructose glucose sucrose/turanose, melezitose, raffinose, and stachyose. Presence of melezitose and stachyose indicated that black flies had fed on homopteran honeydew. Significantly more female (40.0%) than male flies (27.5%) fed on honeydew, and this difference was caused by a skewedness in the morning samples.

Animals↗
PubMed1998

Effects of preservation methods, parasites, and gut contents of black flies (Diptera: Simuliidae) on polymerase chain reaction products.

Molecular analysis of biological specimens usually requires extraction of high-molecular weight DNA free of foreign DNA contaminants. DNA was extracted from black flies at different life stages that had been preserved by 4 methods: larvae and adults in ethanol, larvae in Carnoy's solution, adults on card-points, and adults hand-swatted and sun-dried. Using specific primers for the mitochondrial ND4 gene, a 257-bp amplicon was obtained from specimens preserved by ethanol, card-point mounting, and sun-drying. Successful amplification often required DNA dilutions > or = 1:20 (< 1-10 ng). DNA from specimens preserved in Carnoy's solution (ethanol: acetic acid, 3:1) yielded degraded DNA, resulting in fewer successful amplications. Parasitic nematodes and, to a lesser extent, gut contents resulted in extra products when amplified with randomly amplified polymorphic DNA (RAPD) primers. Sufficient DNA was extracted from the head of a larva for a successful polymerase chain reaction (PCR), eliminating the need to remove the contaminating gut and parasites.

Animals↗
PubMed1999

New cytotype in the Simulium metallicum complex (Diptera: Simuliidae) from Cundinamarca, Colombia.

Polytene chromosomes (n = 108) and morphology (n = 22) of Simulium metallicum Bellardi were described from larvae collected in different localities in Cundinamarca, Colombia, and compared with the standard polytene chromosome banding patterns of S. metallicum A. Polytene chromosomes of S. metallicum from Cundinamarca were characterized by a fixed inversion on the IIL chromosome arm (IIL-22), by 2 sex-linked inversions (IIL-24 and IIL-25), 6 floating inversions, and a heteroband in the IIIS chromosome arm. This taxon was considered to be a cytotype distinct from the 11 members of the S. metallicum complex from Central and South America, and we propose here the name S. metallicum L, following the convention for naming cytotypes in this species complex. There were slight larval morphological differences between S. metallicum from Cundinamarca and S. metallicum A and S. horacioi Okazawa & Onishi (or S. metallicum H).

Animals↗
PubMed1999

Black flies (Diptera: Simuliidae) of the Special Province of Aceh, Indonesia.

The black fly fauna of the Special Province of Aceh, Indonesia, was surveyed in 24 streams in 5 regencies, from 7 to 13 June 1998. Ten species were identified, Simulium (Nevermannia) aureohirtum Brunetti, S. (Gomphostilbia) duolongum Takaoka & Davies, S. (G.) sheilae Takaoka & Davies, S. (G.) sundaicum Edwards, S. (S.) nobile de Meijere, S. (S.) fenestratum Edwards, S. (S.) argyrocinctum de Meijere, S. (S.) nebulicola Edwards, S. (S.) iridescens de Meijere, and S. (S.) minangkabaum Takaoka & Sigit. These species are essentially oriental in distribution, because they belong to the 3 subgenera that are dominant groups in oriental or Palaearctic regions, or both.

Animals↗
PubMed2005

Chromosomal localization of two antihemostatic salivary factors in Simulium vittatum (Diptera: Simuliidae).

The chromosomal locations of two genes encoding the salivary protein products Simulidin (SVAT) and Simulium vittatum erythyma protein (SVEP) were identified using high-resolution cytogenetic mapping. Chromosomal subsection levels were determined from larval and adult salivary gland polytene chromosomes and adult Malphigian tubule chromosomes. Syntenic relationships occurred for both loci from a wild population of Simulium vittatum IIIL-1 collected in central Alabama and the colonized IS-7 S. vittatum sibling. cSVAT mapped to the short arm of chromosomes III, IIIS-72a4.5 and cSVEP mapped to the long arm of chromosome III, IIIL-96b1. cSVAT sits proximal to a common IIIS-2 paracentric inversion, which occurs predominately as the standard sequence in the IIIL-1 sibling and as the inverted sequence in the IS-7 sibling. cSVEP sits close to the differentiated X chromosomes in the IIIL-1 sibling.

Alabama↗
PubMed1996

Intra-specific heterogeneity of the rDNA internal transcribed spacer in the Simulium damnosum (Diptera: Simuliidae) complex.

The internal transcribed spacer (ITS) of the rRNA gene cluster has been used as a model for the study of the action of concerted evolution and molecular drive on repeated sequence families. In contrast to this general finding, preliminary DNA sequence analysis of cloned representatives of the ITS from the West African black fly species complex Simulium damnosum s.1. demonstrated extensive intra-individual and intra-specific polymorphisms. Variability in the ITS was primarily confined to the ITS1 domain. The degree and type of intra-individual and intra-specific variability within the ITS was further characterized using gel electrophoresis, DNA hybridization, and heteroduplex analysis of the PCR products generated from the ITS1 domain. ITS1 copies from individual S. damnosum s.1. differed in length and sequence composition. These results, when taken together, demonstrate that a large degree of intra-individual and intra-specific heterogeneity exists in the ITS of S. damnosum s.1. The intra-individual heterogeneity was greater in the savanna-dwelling than forest-dwelling sibling species of S. damnosum s.1. This heterogeneity may be due in part to inter-breeding among sympatric sibling species, coupled with disturbance of S. damnosum s.1. populations resulting from intensive vector control efforts.

Animals↗
PubMed1991

Oviposition habits of a univoltine blackfly, Prosimulium kiotoense (Diptera: Simuliidae), in Kyushu, Japan.

Oviposition habits of a univoltine mammalophilic blackfly, Prosimulium kiotoense Shiraki, were investigated at a stream in Kyushu Island, Japan. The flies oviposited on bryophyte mosses growing on river bank rock surfaces. The eggs were laid singly, but large irregular egg masses were often formed because many females oviposited within the same small areas. Wet sites with dense bryophyte cover at heights between 0 and 15 cm above water level were selected for oviposition. Oviposition activity was observed in the latter half of April. P. kioteonse females came to the site to lay eggs after 11.00 hours in the morning, when air temperature rose to about 15 degrees C. Peak ovipositional activity occurred between 12.00 and 14.00 hours.

Animals↗
PubMed1992

DNA probes for the identification of members of the Simulium damnosum complex (Diptera: Simuliidae).

Genomic libraries in plasmid have been constructed from various sibling species of blackflies of the Simulium damnosum complex from West Africa. Three cloned repetitive sequences, which show variation in copy number between sibling species, have been isolated. These clones can be used as probes for the dot-blot identification of larvae, pupae or adults into the three main West African subcomplexes, i.e. damnosum, squamosum and sanctipauli subcomplexes. The sequences also show some intraspecific variation in copy number.

Animals↗
PubMed1995

Cytogenetical analysis of the Simulium damnosum complex (Diptera: Simuliidae) in Guinea Bissau.

In a 3-year study during 1990-92, larval collections of the Simulium damnosum complex from the River Corubal system in Guinea Bissau revealed that the only sibling species present were S. sirbanum and the Konkouré form of S.konkourense, but not S.damnosum s.s. which had been found at some of the localities (Saltinho and Cusselinta) in a previous survey by Quillévéré et al. (1981). Their differential distributions were seasonally consistent between years. S. sirbanum was concentrated in the upper reaches of the Corubal, moving downstream at the end of the dry season to exploit new breeding grounds, whereas S. konkourense seemed to be concentrated in the lower reaches and moved upstream in the middle of the dry season. Since the previous survey, it appears that S. konkourense has largely replaced S. sirbanum and S. damnosum s.s. in the lower reaches of the Corubal. S. sirbanum was consistently associated with man-biting behaviour and, although infection studies were not performed, it is likely that S. sirbanum is the main vector of onchocerciasis in Guinea Bissau as S. konkourense does not seem to be anthropophilic. Among five polymorphic inversions in S. sirbanum, the frequency of inversion IL-B increased during the dry season; IL-2 and IIL-7 showed homozygous disadvantage whereas IIL-3 and IIIL-6 did not; IS-2 tended to be fixed in all populations. Simulium konkourense populations in the River Corubal differ from those found upstream in its tributary the River Koumba, in the Fouta Djallon of Guinea, by their sex chromosomes (having no sex-linked inversions) and biting preferences, indicating that the populations are not freely interbreeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Africa, Western↗
PubMed1995

Salivary apyrase in New World blackflies (Diptera: Simuliidae) and its relationship to onchocerciasis vector status.

Salivary gland apyrase is believed to be critical to blood-feeding in arthropod vectors. This enzyme was measured in six New World blackflies representing three taxonomic pairs of non-vectors and vectors of Onchocerca volvulus. In Simulium (Psilopelmia) ochraceum, a highly anthropophilic vector in Mexico and Guatemala, apyrase exhibited maximum activity between pH 8.0 and 9.0, mean 39.8 +/- 4.7 milliUnits/pair of gland equivalents (mU), and was enhanced when ATP was used as a substrate. In the zoophilic non-vector Simulium (Psilopelmia) bivittatum maximum activity was significantly less (5.1 +/- 0.7 mU) under all conditions examined. Preference for ADP or ATP as substrate was a function of the pH of the reaction for this species. Apyrase activity in Simulium (Simulium) metallicum Bellardi (29.5 +/- 11.5 mU), a zoophilic secondary vector in Mexico and Guatemala, resembled that of S. (Ps.) ochraceum (24.8 +/- 13.7 mU at pH 8.5) with ADP as substrate, but showed reduced activity with ATP. Both these Central American vectors had higher apyrase activity than found in Simulium (Notolepria) exiguum, a vector of O. volvulus in Ecuador and Colombia. However, maximum apyrase activity, measured at pH 8.0 with ADP as substrate, was greater in S. (N.) exiguum (10.9 +/- 0.6 mU) than in Simulium (Notolepria) gonzalezi (5.9 +/- 1.9 mU), a non-vector species widespread in Central America. Therefore, for the consubgeneric species pairs examined, a positive association was detected between higher concentrations of apyrase activity and their vector status for O.volvulus.

Adenosine Diphosphate↗
PubMed1996

Effect of weather conditions on the flight activity of Nigerian blackflies (Diptera:Simuliidae).

A vehicle-mounted net was used to make hourly catches of blackflies at 700-1000 m altitude in the River Assob valley, central Nigeria, on 20 days during the dry season. Pearson Correlation Matrix analysis of the collection data and meteorology showed that the main factors affecting flight activity of each of the four most abundant blackfly species were primarily light intensity and secondly wind velocity, whereas relative humidity was the least important factor. Flight activity showed a negative linear regression against wind, with some activity occurring in wind speeds up to 15 km/h. Distance-weighted least-squares (DWLS) regressions showed little correlation of temperature with activity for Simulium hargreavesi and S.adersi, but S.squamosum and S.vorax had small peaks at 28 degrees C and 31 degrees C, respectively. DWLS regression against light intensity showed an activity peak at 6000 lux, except in Simulium adersi.

Animals↗
PubMed2005

Phylogeography of the black fly Simulium tani (Diptera: Simuliidae) from Thailand as inferred from mtDNA sequences.

Intraspecific phylogeography has been used widely as a tool to infer population history. However, little attention has been paid to Southeast Asia despite its importance in terms of biodiversity. Here we used the cytochrome oxidase I gene of mitochondrial DNA (mtDNA) for a phylogeographic study of 147 individuals of the black fly Simulium tani from Thailand. The mtDNA revealed high genetic differentiation between the major geographical regions of north, east and central/south Thailand. Mismatch distributions indicate population expansions during the mid-Pleistocene and the late Pleistocene suggesting that current population structure and diversity may be due in part to the species' response to Pleistocene climatic fluctuations. The genealogical structure of the haplotypes, high northern diversity and maximum-likelihood inference of historical migration rates, suggest that the eastern and central/southern populations originated from northern populations in the mid-Pleistocene. Subsequently, the eastern region had had a largely independent history but the central/southern population may be largely the result of recent (c. 100,000 years ago) expansion, either from the north again, or from a relictual population in the central region. Cytological investigation revealed that populations from the south and east have two overlapping fixed chromosomal inversions. Since these populations also share ecological characteristics it suggests that inversions are involved in ecological adaptation. In conclusion both contemporary and historical ecological conditions are playing an important role in determining population genetic structure and diversity.

Animals↗
PubMed1996

Cytotaxonomic identifications of the Simulium damnosum complex (Diptera:Simuliidae) from Nigeria.

Cytotaxonomic analysis of Simulium damnosum s.l. larvae collected from 23 sites across 4 bioclimatic zones in Nigeria revealed the presence of 5 cytospecies (S. damnosum s.str., S. sirbanum, S. squamosum, S. yahense and S. soubrense (including the Beffa form). The biogeographical distribution of the sibling species was mostly similar to that observed further west in the OCP area, although geographic cytotaxonomic variation was recorded in S. squamosum, S. damnosum s.str. and S. sirbanum. Some aspects of the chemical and physical environment of the breeding habitats were investigated.

Animals↗
PubMed2004

Two new cytoforms of the Simulium damnosum complex (Diptera: Simuliidae) from Malawi and Tanzania and potential onchocerciasis vectors.

During a distribution survey of Simulium damnosum s.l. around the Tukuyu onchocerciasis focus at the northern tip of Lake Malawi/Nyasa (Tanzania), we discovered two new cytoforms of the S. damnosum complex in onchocerciasis-free areas. The Nyika form is related to Simulium thyolense, a vector of onchocerciasis, and can be identified by the new inversion 3L-L on the long arm of chromosome 3. It was found breeding in five rivers in northern Malawi and neighbouring Tanzania and is assumed to be zoophilic. The Njombe form represents a member of the Sanje group of the complex and is characterized by the new diagnostic inversion 2L-35 on chromosome 2. So far, it is only known from around Njombe town in southern Tanzania, where it breeds at remarkably high altitudes. Anthropophily for the Njombe form is well known. The medical importance and systematic position of the new forms within the S. damnosum complex are discussed.

Altitude↗
PubMed2004

Molecular differentiation of two sibling species of the black fly Simulium vittatum (Diptera: Simuliidae) based on random amplified polymorphic DNA.

Larvae of the black fly morphospecies Simulium vittatum from Colorado, Montana, Nebraska, and New Hampshire were cytologically identified as either the IS-7 or the IIIL-1 cytospecies. DNA was PCR amplified from cytotyped larvae using eight 10-mer primers, labeled with 33P, and run on polyacrylamide gels. The entire data set of 96 amplicons produced incomplete separation of the two cytospecies when subjected to neighbor-joining and maximum parsimony analyses. However, when analyzed within geographical regions, separate species status was supported. Bootstrap support for distinctness of the two cytospecies was best in Colorado where they were collected in true sympatry. The IS-7 cytospecies was more polymorphic in the western states, where it differed most from IIIL-1, which was most variable in the eastern states. The frequencies of the 17 most common amplicons in the two cytospecies were inversely correlated. A model of speciation derived from the molecular evidence suggests that IS-7 evolved in the west and spread eastward, whereas IIIL-1 later originated in the east and spread westward.

Animals↗