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PubMed1977

Studies on the attraction of Simulium damnosum s.l. (Diptera: Simuliidae) to its hosts. II. The nature of substances on the human skin responsible for atrractant olfactory stimuli.

In the Cameroon rain-forest, electric fan traps, baited with trousers which had been worn by men for several days, captured more females of S. damnosum s.l. than did traps baited with worn shirts of similar material. A number of human body fluids were used as bait, but only sweat appeared to contain the olfactory attractant(s). The fluid portion of filtered arm sweat attracted more flies than did the residue. The attractant substances from human skin would not dissolve directly in organic solvents, but when an artificial sweat solution was used to swab men's arms and legs, and this was then saturated with salt and shaken with an organic solvent, the extract was attractive to S. damnosum. Treatment of attractive worn cloths with dilute aqueous solutions of hydrochloric acid, sodium hydroxide or mercuric chloride greatly reduced their attractiveness. A number of organic compounds which occur on the human skin were found to be ineffective as attractants.

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PubMed1977

Studies on the attraction of Simulium damnosum s.l. (Diptera: Simuliidae) to its hosts. III. Experiments with animal-baited traps.

In the forest zone of the United Republic of Cameroon, a live chicken proved far more attractive to hunting S. damnosum s.l. than did a live sheep; but in the Sudan-savanna zone, a sheep was more attractive than a chicken. It is suggested that the populations of flies in the two areas represented different species of the S. damnosum s.l. complex with different host-finding mechanisms, that in the forest (? S. squamosum) hunting mainly by smell, and that in the Sudan savanna (? S. damnosum s.s.) hunting mainly by sight.

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PubMedDate not supplied

[Studies on Aureum-group (Diptera, Simuliidae) in France (author's transl)].

The study of the male genitalia of blackflies of the complex "Aureum", from several areas of France, has shown four morphological types which are distinquishable by the structures of the ventral plate and of the sytles. These four are S. (E.) aureum Fries, 1824 sensu Rubzov, 1962, S. (E) angustipes Edwards, 1915, S. (E.) lantinum (Rubzov, 1962) and S. latizonum (Rubzov, 1956). S. aureum, sensu Rubzov and S. angustipes, Newly found in France, were collected in Brittany; S. latizonum was found in the south of the Massif Central and S. latinum in both regions. In each case the taxonomy and distribution are given. These four species have a large western palearctic distribution, and the regrouping of several recently described taxa would be useful within the complex "Aureum".

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PubMedDate not supplied

[Swarming of blood-sucking flies (Simuliidae) in Siberia].

During the swarming period of black flies aggregations of the mass species Schönbaueria pusilla Fries and Simulium truncatum Lundstr. (Jakutia), Byssodon maculata Mg. and S. longipalpe Belt. (Tomsk and Novosibirsk regions, Lower Priamurje) were noted. Observations on the time and character of swarming, statial distribution of swarming black flies and on weather conditions were conducted.

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PubMed1997

[Natural vector capacity level of Simulium damnosum s.l. (Diptera: Simuliidae) at the ecology station of Tai (Côte d'Ivoire)].

Several studies have been carried out on the transmission of Onchocerciasis by Simulium damnosum s.l. in the forest zone of Côte d'Ivoire. This study, carried out in 1979-1980 was devoted to determine the risk of onchocerciasis transmission inside and outside the rain forest of Taï (5 degrees 50' N-7 degrees 25' W). We present the vectorial capacity of S. sanctipauli in the region of Taï before massive flow of refugees from areas of Liberia without any control Programme. The results of micromorphological technics for determination of S. damnosum adults, showed that mainly females of S. sanctipauli were present. The studied populations had low parturity rates: 39.2% outside and 30.9% of parous flies inside the rain forest. The parasitic rates (0.4% of infectious females outside and 0.1% inside) and their parasitic loads (15 and 3 infective larvae per 1000 parous female respectively outside and inside the rain forest) were low, consequently their vectorial capacity with Onchocerca volvulus was almost non-existent in natural conditions. Before massive flow of refugees including persons carrying microfilariae, there were no problem of onchocerciasis within and outside the rain forest of Taï. However, the massive flow of refugees and the deforestation for growing crops can create situations favourable to the installation of more efficient vectors, increase man/vector contact and contribute to more intense onchocerciasis transmission. The monitoring of onchocerciasis transmission is necessary.

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PubMed2003

Dipteran predators of Simuliid blackflies: a worldwide review.

Haematophagous female blackflies (Diptera: Simuliidae) are serious biting pests and obligate vectors of vertebrate pathogens, namely filarial Dirofilaria, Mansonella, Onchocerca and protozoal Leucocytozoon. Immature stages of Simuliidae inhabit lotic waterways, the sessile larvae filter-feeding and often forming a large proportion of the benthic biomass, usually aggregated in well-oxygenated sections of streams, rivers, waterfalls and spillways. Simuliid control practices depend on larvicidal chemicals, biological products (bacteria, nematodes) and environmental modification. The potential use of predators for biological control of Simuliidae has not been exploited. Predators of Simuliidae include examples of at least 12 families of Diptera and other predaceous arthropods (Crustacea and insects: Coleoptera, Odonata, Plecoptera, Trichoptera), invertebrates (notably Turbellaria), as well as browsing fish. Diptera impacting upon simuliid populations comprise mainly Chironomidae, Empididae and Muscidae, although several other families (Asilidae, Dolichopodidae, Phoridae, Drosophilidae, Scathophagidae) play a significant role as predators. Details of predator and prey species and life stages are presented, by zoogeographical region, including the prevalence of cannibalism among Simuliidae.

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PubMed1957

Simuliid vectors of onchocerciasis in Guatemala.

Simulium ochraceum, S. metallicum and S. callidum are the three species of Simuliidae which are known to transmit onchocerciasis in Guatemala. Of these, S. ochraceum is often the most prevalent and displays the highest degree of anthropophily. Other potential vectors exist, but have never been found to harbour developing forms of Onchocerca.The average flight range of these insects was found to be about 7.5 miles, although they may be transported greater distances while feeding on horses.The Simuliidae are most prevalent in December, after which their density decreases, reaching its lowest level in June-August.Large-scale dissection of Simuliidae specimens has revealed the presence of metacyclic forms either in a free state in the abdomen or, as in the majority of cases, lodged in the Malpighian tubes. There was no indication of metacyclic forms in the cephalic region of the insect.

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PubMed2001

Temephos-resistant larvae of Simulium sanctipauli associated with a distinctive new chromosome inversion in untreated rivers of south-western Ghana.

Larvae of the Simulium damnosum Theobald complex (Diptera: Simuliidae) were sampled in June 1996 from two sites in south-west Ghana where larviciding has not been applied: Sutri Rapids on the Tano river (05 degrees 23 minutes N 02 degrees 38 minures W) and Sekyere-Heman on the Pra river (05 degrees 11 minutes N 01 degrees 35 minutes W). All specimens were identified as Simulium sanctipauli Vajime & Dunbar sensu stricto (Diptera: Simuliidae). Bioassays with temephos (organophosphorus larvicide employed by the Onchocerciasis Programme for systematic treatment of most rivers across West Africa since the 1970s) showed about five-fold resistance in the Tano population (LC95 2.37-3.14 mg/L) and slight tolerance to temephos in the Pra population (LC95 0.67-0.76 mg/L), vs. the diagnostic concentration of 0.625 mg/L. Larval salivary polytene chromosomes of S. sanctipauli showed fixed inversions 1S-24/24, standard IIL-6 and a new inversion IL/36 polymorphism at Sutri on the Tano. These karyotype characteristics differ from those of temephos-resistant S. sanctipauli in rivers of C te d'Ivoire and other sites on the Tano in Ghana. Thus, temephos resistance in S. sanctipauli at Sutri is associated with distinct chromosomal configurations, showing that immigration was unlikely. This resistance could have been locally selected by exposure of S. sanctipauli larval populations to agrochemicals run-off from cocoa, coffee and oil plantations flanking the rivers.

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PubMed2002

Completion of the sequence of the nuclear ribosomal DNA subunit of Simulium sanctipauli, with descriptions of the 18S, 28S genes and the IGS.

We describe the IGS-ETS, 18S and 28S ribosomal gene sequences of Simulium sanctipauli Vajime & Dunbar, a member of the S. damnosum Theobald (Diptera: Simuliidae) complex of blackflies (Diptera: Simuliidae). These regions, together with the ITS-1, ITS-2 and 5.8S rDNA presented elsewhere (accession number U36206), constitute the composite sequence of the entire rDNA unit, making S. sanctipauli the second dipteran species of medical importance for which the entire rDNA has been sequenced. Despite the lack of sequence identity, the IGS of S. sanctipauli showed some structural similarities to other Diptera, i.e. the mosquito Aedes albopictus Skuse (Culicidae), the fruitfly Drosophila melanogaster Meigen (Drosophilidae) and the tsetse Glossina (Glossinidae). Two blocks of tandemly repeated subunits were present in the IGS of S. sanctipauli and, unlike other species of Diptera, they contained no duplications of promoter-like sequences. However, two promoter-like sequences were identified in the unique DNA stretches of the IGS by their sequence similarity to the promoter of Aedes aegypti L. (Diptera: Culicidae). The observed sequence variation can be explained, as in the case of Drosophila spp., by the occurrence of slippage-like and point mutation processes, with unequal crossing-over homogenizing (to a certain extent) the region throughout the gene family and blackfly population. The 18S and 28S rDNA genes show more intraspecific variability within the expansion segments than in the core regions. This is also the case in the interspecific comparison of these genes from S. sanctipauli with those of Simulium vittatum, Ae. albopictus and D. melanogaster. This pattern is typical of many eukaryotes and likely to be the result of a more relaxed functional selection in the expansion segments than on the core regions. The A + T content of the S. sanctipauli genes is high and similar to those of other Diptera. This could be the result of a change in the mutation pressure towards AT in the Diptera lineage.

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PubMedDate not supplied

Laboratory investigations of trichomycete prevalence, abundance and fecundity in a Smittium-simuliid model.

Smittium, the most speciose genus of the "gut fungi" (Zygomycota: Trichomycetes), is found attached to the hindgut cuticle of larval aquatic Diptera. Smittium spp. colonize several host families (e.g., Smittium culisetae in Chironomidae, Culicidae and Simuliidae), but some species appear to be specific to a single host family (e.g., Smittium morbosum Sweeney in Culicidae). The specificity of Smittium spp. within a host family has been difficult to resolve. This research presents evidence that certain Smittium spp. differentially colonize particular species of black fly (Diptera: Simuliidae) hosts as measured by differences in prevalence, abundance and fecundity. Reasons for this differential occurrence and fecundity in hosts are unclear but might include fungal responses to variations in host morphology, physiology, distribution or behavior. Variable fitness of Smittium spp., within a suite of available hosts, could be a factor in the diversity of this fungal group.

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PubMed2003

Trichomycetes (Zygomycota) in the digestive tract of arthropods in Amazonas, Brazil.

Eight species of Harpellales and three species of Eccrinales (Zygomycota: Trichomycetes) were found associated with the digestive tract of arthropods from terrestrial and aquatic environments in the central Amazon region of Brazil. New species of Harpellales include: Harpella amazonica, Smittium brasiliense, Genistellospora tropicalis in Simuliidae larvae and Stachylina paucispora in Chironomidae larvae. Axenic cultures of S. brasiliense were obtained. Probable new species of Enterobryus (Eccrinales), Harpella, and Stachylina (Harpellales) are described but not named. Also reported are the previously known species of Eccrinales, Passalomyces compressus and Leidyomyces attenuatus in adult Coleoptera (Passalidae), and Smittium culisetae and Smittium aciculare (Harpellales) in Culicidae and Simuliidae larvae, respectively. Comments on the distribution of some of these fungi and their hosts in the Neotropics are provided.

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PubMed2000

Differential toxicity of leaf litter to dipteran larvae of mosquito developmental sites.

The relative toxicity of leaf litter to nematocerous dipteran larvae characteristic of mosquito developmental sites was investigated. Culicidae, Chironomidae, and Simuliidae taxa originating from alpine hydrosystems were tested together with two laboratory nonindigenous culicid taxa. Bioassays indicate that ingestion of 10-month-old decaying leaves from Alnus glutinosa, Populus nigra, and Quercus robur by larvae is more deleterious for Aedes aegypti, A. albopictus, Culex pipiens, Simulium variegatum, and Chironomus annularius than for A. rusticus. Histopathological observations reveal that the midgut epithelium is the main target organ of the toxic effect of dietary leaf litter, which appears to be stronger than that of previously reported tannic acid. There is a general response of the nematocerous larval midgut epithelium to dietary tannins-phenolic compounds: clear cells of the anterior midgut showing symptoms of intoxication before dark cells of the posterior midgut.

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PubMed1993

Onchocerciasis in British cattle: a study of the transmission of Onchocerca sp. in north Wales.

The transmission of bovine Onchocerca spp. in Britain was investigated by studying the Ceratopogonidae and Simuliidae which attacked bait cattle between April and October at two sites in North Wales, where either Onchocerca lienalis and O. gutturosa (Cynwyd), or O. lienalis alone (Pentrefoelas) occurred. Based on the relative abundance of each species, their seasonal variation in abundance and preferential feeding sites on cattle, the presence of Onchocerca sp. infective larvae and the development of patent infections in bait cattle, vectors were identified as Simulium ornatum s.1. at Pentrefoelas and S. reptans at Cynwyd (0.5% and 1.5% of parous flies infective, respectively). There was no significant difference between the lengths of the infective larvae from vectors at either site (Pentrefoelas: mean = 543.5 microns, SD = 29.45; Cynwyd: mean = 550.86 microns, SD = 35.26; p > 0.1), which were consistent with descriptions of O. lienalis. The identity of a vector for O. gutturosa was not determined and the role of certain candidates is discussed. In this respect, the absence of Culicoides nubeculosus was notable. Transmission of Onchocerca sp. was limited to a short period of about 8 weeks, by a combination of vector abundance and parasite uptake from dermal skin layers, and a mean daily temperature requirement of 15 degrees C or more for complete parasite development in the vector. The effect of this temperature restriction in relation to the geographical distribution of the two species is discussed.

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PubMed2001

Sex chromosome variation and cytotaxonomy of the onchocerciasis vector Simulium squamosum in Cameroon and Nigeria.

On the basis of sex chromosome variation, three cytotypes of Simulium squamosum (Enderlein) (Diptera: Simuliidae) are described from Cameroon and Nigeria. Simulium squamosum A is the typical form as originally described by Vajime & Dunbar (1975) with chromosome I as the sex chromosome. It occurs throughout most of Cameroon and south-east Nigeria. A second cytotype, S. squamosum B, is described from the river Sanaga (Cameroon). It also has chromosome I as the sex chromosome, but the nature of the sex differential region is different. Simulium squamosum C has no sex-linked chromosomal rearrangements. It is widespread in Nigeria and occurs near Mount Cameroon, where it seems to hybridize with S. squamosum A.

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PubMed1998

Distribution of the Simulium damnosum complex on Bioko island, Equatorial Guinea, and the potential for onchocerciasis elimination by vector eradication.

Onchocerciasis is endemic on the island of Bioko, Equatorial Guinea, where it is transmitted by the 'Bioko form' of the Simulium damnosum complex, a cytospecies unique to the island. To determine the distribution of vector breeding, three dry season and two wet season expeditions were made in 1989, 1996 and 1997, and 226 of the island's 247 rivers (91.5%) were visited. Of these 226 rivers, 130 (58%) were flowing during the dry season, forty-five (20%) supported aquatic stages of Simuliidae of any species and twenty-five (11%) contained larvae or pupae of the S. damnosum complex. The twenty-one rivers not prospected were in the mountainous south of the island, where an additional seventeen rivers were reached but not satisfactorily prospected. Of these thirty-eight rivers, twenty-nine were considered highly likely to support vector breeding, bringing the total number of rivers which could harbour the vector during the dry season to fifty-four (21.9% of the island's total). Breeding was believed to be limited to river stretches below 1000 m altitude, and during the dry season the total length of those stretches which could support breeding on Bioko was estimated to be 1020 km. A combination of factors, including low river discharges during the dry season, the relatively low water temperature on Bioko, the suitability of limited stretches of most rivers as vector breeding sites and the close proximity of many rivers within a small geographical area, render the vector vulnerable to eradication by aerial treatment of rivers with insecticide. The isolation of the Bioko form of the S. damnosum complex suggests that reinvasion following treatment would be unlikely, and eradication of the vector might be achieved by a dry season larviciding programme in one or two years.

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