Black Fly Species Research Articles

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.

Mitochondrial transfer RNA genes in a black fly, Simulium vittatum (Diptera: Simuliidae), indicate long divergence from mosquito (Diptera: Culicidae) and fruit fly (Diptera: Drosophilidae).

Sequences are given for nine complete genes and one partial mitochondrial tRNA gene of the black fly, Simulium vittatum (Zetterstedt). Sequenced tRNA genes were for alanine, arginine, asparagine, aspartic acid, glutamic acid, glycine, leucine(CUN), lysine, serine(AGN), and valine. Nucleotides were aligned with the same previously sequenced genes in Aedes albopictus Skuse and Drosophila yakuba Burla. A cluster of six tRNA genes, which differ in arrangement in Ae. albopictus and D. yakuba, was amplified by PCR and found to have the same position and orientation in S. vittatum as in D. yakuba. Overall, similarity with either D. yakuba or Ae. albopictus was 86%. Sequences that were common to the three insects suggest that black flies and mosquitoes are as divergent from each other as either is from Drosophila. Sequences for nine species of black flies were obtained for tRNA leucine(CUN) from DNA amplified with another primer set. Little variation occurred within the tRNA gene but, by including the flanking regions to provide 175 base pairs, a phylogeny of the nine species was obtained that was largely consistent with current classification.

New Species of Black Fly in the Simulium jenningsi Group (Diptera: Simuliidae) from the Southeastern United States

The larva, pupa, adults, and polytene chromosomes of a new species of black fly (Diptera: Simuliidae) in the Simulium jenningsi group are described and illustrated, and the taxonomy and ecology of the group are discussed. Simulium krebsorum Moulton & Adler, new species, occurs in small, swamp streams of the Sandhills and Upper Coastal Plain of South Carolina and Upper Coastal Plain of North Carolina. The pupa and male of this species are readily distinguished from those of all other North American species. The polytene chromosomes are a minimum of 11 fixed inversions from the Simulium jenningsi standard.

Two new blackfly species of Simulium (Simulium) from Java, Indonesia (Diptera: Simuliidae).

Two new blackfly species, Simulium (Simulium) sigiti sp. nov. and S. (S.) javaense sp. nov. are described based on the female, male, pupal and larval specimens collected from Java. Simulium (S.) sigiti is characterized by the presence of a pit-like cuticular organ at the base of pupal gill, as well as shortened pupal filaments. This is the first species of the tuberosum group from Java. The variety of S. (S.) iridescens De Meijere, 1913 is here elevated to the species status and is given a new specific name S. (S.) javaense sp. nov. This new species is easily distinguished from S. (S.) iridescens by the inflated gill filaments, the absence of tubercles on the cephalic and thoracic integuments of the pupa, and the russet body coloration of the larva.

A revisionary note on the blackfly, hitherto called "Simulium (Gomphostilbia) batoense Edwards, 1934" from the Ryukyu Islands, Japan (Diptera: Simuliidae).

A new species name, Simulium (Gomphostilbia) yaeyamaense sp. nov. is proposed for the blackfly species in the Ryukyu Islands which has been hitherto regarded as S. (G.) batoense Edwards, 1934, originally described from Java. The new species is readily distinguished from S. (G.) batoense by the large basal tooth on the female claws, the characteristic pruinose pattern on the male scutum, and the branching of the pupal gill filaments. Revised descriptions are given for female, male, pupa and mature larva of this new species, and discussed are also taxonomic affinities with related species.

SEASONAL ACTIVITY OF FEMALE BLACK FLIES (DIPTERA: SIMULIIDAE) IN PASTURES IN NORTHEASTERN SASKATCHEWAN

AbstractThe black fly species Simulium luggeri Nicholson and Mickel s.l., S. vittatum Zetterstedt s.l., S. venustum Say s.l., S. verecundum Stone and Jamnback s.l., and S. decorum Walker s.l. were collected in silhouette traps near Prince Albert, Sask., in 1986, and near Choiceland, Sask., from 1986 to 1988. The Prince Albert site was located between and within 2 km of the North and South branches of the Saskatchewan River and was 25 and 60 km south of the Whitefox River and Torch River systems. The Choiceland site, 60 km east of the Prince Albert site, was 15 km north of the main branch of the Saskatchewan River and 1/2 and 25 km south of the Whitefox River and Torch River, respectively. Simulium luggeri was the most abundant species collected at the Prince Albert site whereas S. luggeri, S. vittatum, and the S. venustumlverecundum complex were approximately equally abundant in trap catches near Choiceland over the entire season but in each study year a seasonal progression in peak abundance occurred. Black fly numbers in sweep net collections taken once, in the middle of the day, were weakly correlated with numbers in silhouette trap collections taken during an entire day.

Distribution and ecology of benthic macroinvertebrates in the Opunohu river catchment, Moorea, French Polynesia

Distribution and ecology of macroinvertebrates in the Opunohu River catchment (17°31'S, 149°S 50'W), Moorea, French Polynesia, were studied at eight sites, which range in altitude from 2 to 335 m, and from 0.4 to 4.0 km distance from the ocean. Taxa richness per site ranged from 16 to 28, and was higher in austral spring than austral fall ; 48 taxa were collected over all sites and included 7 species of molluscs, 6 crustaceans, 23 insects, and 6 oligochaetes. Neritid snails and atyid and palaemonid shrimp in the Opunohu have diadromous life cycles : they enter freshwater as juveniles and migrate upstream ; their larval offspring must return to the sea for growth and metamorphosis. These groups generally had larger individuals at upstream than at downstream sites. Human activities such as channeling stream flow through elevated culverts can impede normal upstream migration of diadromous species. Densities of neritid egg capsules were higher in riffle than pool habitats, exhibited seasonality, and were highest at the downstream-most site ; abundance at upstream sites also reflected local habitat conditions. Microhabitat segregation of two species of atyiid shrimp reflected their respective filter-feeding and detritus-gathering feeding mechanisms. High pH and temperatures in the poorly buffered, cascade headwaters produced high seston loads (3.4 mg/l) that mainly contained diatoms ; in downstream reaches seston concentrations were lower and contained more detritus. Some filter-feeding black fly species occured only in the headwaters. Insect taxa-richness was higher in headwater reaches while mollusc and crustacean richness was higher at sites near the ocean, which supports a tenet of the River Continuum Concept.

A Conceptual Model for the Estimation of the Sensitivity of Black Fly Larvae to Bacillus thuringiensis var. israelensis

Results from bioassays of a commercial formulation of Bacillus thuringiensis var. israelensis (Teknar HP-D) are combined with an empirical model of the feeding rate of larvae of a target species of black fly (Simulium venustum/verecundum) to develop a model relating the mortality of larvae to the amount of formulation ingested per unit mass of larvae (specific ingested dose). LD50 of Teknar HP-D was about 1 μg wet mass of Teknar per milligram dry mass of larvae, and independent of size of the larvae and seston concentration. Compared with standard assay analysis relating the mortality to the dose (milligrams per litre times seconds), the proposed model allowed more precise and replicable estimation of the effective dose. Reanalysis of published data on the potency of another Bti formulation (Teknar WDC), confirmed the superiority of the proposed model over the standard procedure. Susceptibility of larvae to particulate larvicides is mainly a function of the larval feeding rate. In addition to size of the larvae, temperature, and seston concentration, analysis of the model reveals that the length of the contact period and the variability of feeding rates among individual larvae are important factors determining the mortality rate following treatments.

Supernumerary chromosome evolution in the Simulium vernum group (Diptera: Simuliidae)

B chromosomes are present in a cluster of closely related species of black fly in the Simulium vernum group including six sibling species within the S. vernum complex, Simulium costatum, and Simulium juxtacrenobium. The S. vernum siblings all possess the same small metacentric supernumerary, while S. juxtacrenobium carries three different supernumeraries (two telocentrics and one metacentric) and S. costatum has both a metacentric and a telocentric B chromosome. Analysis of the polytene chromosomes in the larval salivary glands has revealed relationships between the supernumeraries of the different species. The metacentric B chromosome of the S. vernum siblings apparently results from a fusion of the two telocentric supernumeraries of S. juxtacrenobium. Acquisition of a nucleolar organizer then gave rise to the metacentric B chromosome in S. juxtacrenobium. The acquisition of a nucleolus by a S. juxtacrenobium telocentric gave rise to one of the S. costatum supernumeraries. Two alternate models for the origin of black fly supernumeraries are presented.Key words: supernumerary chromosome, black fly, polytene chromosome, chromosome evolution.

Absence of population structure in black flies as revealed by enzyme electrophoresis

Analysis of allozyme variation by the FST-statistic in Simulium decorum and several other black fly species reveals very little genetic variation that could be attributed to genetic drift. This is consistent with what is known about the rates of migration of black flies and supports the idea that there is a lack of population subdivision in these insects. This picture of population structure is quite different from that presented by chromosome inversion polymorphisms. Chromosomal variation, however, can reasonably be attributed to selection and suggests that the role of inversions in black fly evolution is similar to population subdivision in the shifting balance process.Key words: black flies, allozymes, population structure, evolution.

Chromocentre polymorphism in polytene chromosomes of Simulium costatum (Diptera: Simuliidae)

The polytene chromosomes of the black fly species Simulium (Nevermannia) costatum are joined at the centromeres in a strongly heterochromatic chromocentre. Examination of the larval salivary gland chromosomes revealed two populations with a unique polymorphism for attachment to the chromocentre involving all centromeres. All three homologous pairs of chromosomes are polymorphic for centromeres that do not join to the chromocentre. Samples from one of these populations were large enough for thorough study. In this population, the attachment polymorphism is in Hardy-Weinberg equilibrium for two of the centromeres and was in the same frequency for 2 successive years of sampling. The polymorphism could be either primary, retained from an ancestral nonchromocentric state, or secondary, evolving independently or introduced via hybrid introgression. The evolution of chromocentres is discussed in the context of species in the Simulium vernum group.Key words: black fly, polytene chromosome, chromocentre, polymorphism, evolution.

Autogeny as successful reproductive strategy in high altitude black-flies (Diptera, Simuliidae)

The black-fly fauna of Drovrefjell National Park, Central Norway, was investigated at elevations between 870 m and 1 630 m and covered the sub-alpine, low- and middle-alpine vegetation zones. We found 13 black-fly species and a dominance of three non-bloodsucking species, Prosimulium ursinum, Cnephia tredecimata and Eusimulium crassum, in this area. E. crassum dominated the bog stream habitat, while C. tredecimata and P. ursinum dominated the outlet habitat. The parthenogenesis of P. ursinum is an advantage over a sexual reproduction in the extreme habitat of glacier fed outlets. While mammalophilic species were absent or scarce, we found a high proportion of bird-feeding Eusimulium spp. E. corniferum and E. carpathicum have not been previously recorded from Norway.

The vectoral role of several blackfly species (Diptera: Simuliidae) in relation to human onchocerciasis in the Sierra Parima and Upper Orinoco regions of Venezuela.

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.

Sensilla of haematophagous insects sensitive to vertebrate host-associated stimuli

The morphology of the sensilla sensitive to vertebrate host-associated stimuli is diverse reflecting the numerous independent origins of haematophagy within the insects. Using electron microscopic techniques, the sensilla of mosquitoes and blackflies have been the most thoroughly studied, although numerous works have been conducted on other blood-feeders. Notably lacking are fine structure studies on blood-feeding maggots and ectoparasitic, adult Muscomorpha. In comparing blood-feeders with other insects it becomes apparent that: (1) carbon dioxide plays a significantly greater role in location of food by haematophagous insects than by phytophagous and saprophagous species; (2) only in blood-feeders do the adenosine phosphate nucleotides, a single group of compounds, appear to be the phagostimulants for almost all species; and (3) feeding deterrents are unknown in haematophagous insects. When the sensory complements of the various groups of blood-feeders are compared, three points emerge. First, reduction in numbers of olfactory chemosensilla that mediate odour cues used in long-distance, host-orientation occurs in male nematocerans and in females of completely autogenous species of mosquitoes and black flies. Second, there is a striking correlation between the number of labial chemo- and mechanosensilla and the feeding behaviour of the insect. Third, there is a possible positive correlation between the number of chemosensitive antennal neurones and the distance travelled by the insect to the host.

The influence of water velocity on particle capture by the labral fans of larvae of Simulium bivittatum Malloch (Diptera: Simuliidae)

Larvae of Simulium bivittatum Malloch exposed to water velocities of 3.2–47.0 cm/s consumed a maximum of particles at velocities of 10.0–25.0 cm/s. Larvae consumed significantly fewer particles at velocities below and above the suitable (10.0–25.0 cm/s) range. The inability of larvae to capture particles efficiently at low velocities (3.2–4.5 cm/s) is attributed to the formation of thick boundary layers around filtering structures (labral fans). Steep velocity gradients in the boundary layer around fans and probably high drag forces on fans contribute to the low retention efficiency at high velocities (35.0–47.0 cm/s). The drag forces and the torque on particles at the water–fan interface enhance the adhesion of small (0.5–5.7 μm) particles, which form the bulk of food particles in the guts of larvae. The relevance of this study to the control of larvae of pest species of black flies is discussed.

Distributional patterns of immature Simuliidae (Diptera) in northwestern North America

SUMMARY. 1. Major landscape features and hydrological parameters indicative of black fly species assemblages were examined at 101 stream sites in Alberta, northern British Columbia, the Yukon and Alaska during the summer. Forty‐one black fly taxa were recorded at seventy‐ nine sites using qualitative sampling procedures. River sites lacking black flies had significantly higher conductivity, greater depth, shallower slope and were farther from the Pacific Ocean than sites with black flies.2. Classification of sites by taxon occurrence using hierarchical cluster analysis suggested five groupings: A. Simulium tuberosum(Lundstrëm) complex + several taxa. B, S. venustum Saylverecundum Stone and Jamnback complexes +S, tuberosum complex; C. 5. arcticum Malloch complex +S. corbis Twinn complex; D, Gymnopais Stone/Prosimulium Roubaud; and E. P. onychodactytum Dyar and Shannon complex + several taxa.3. Multiple discriminant analysis (MDA) was used to predict group membership of the seventy‐nine sites using nineteen environmental variables; 71% of the sites were classified correctly. MDA identified latitude and distance from stream source as important factors separating group D from other groups. Stream width and drainage basins entering the Arctic Oeean and Hudson Bay delineated group B. There was no clear separation among groups A. C or E. The presence of sibling species probably accounts for the overlap of black fly assemblages.4. Our findings are briefly discussed in the context of stream classification systems, notably the river continuum concept.

季節的な河川でのブユの出現と Mayacnephia aguirrei の化性

Colonizing order of the blackfly species and voltinism of Mayacnephia aguirrei were studied in seasonal streams in an onchocerciasis-endemic area of Guatemala. Mayacnephia aguirrei colonized first, then Simulium metallicum, S. horacioi and S. ochraceum appeared, followed by S. callidum and S. (Hemicnetha) spp. The colonizing order of these species coincided with the order of a preference for stream discharge from small to large. Mayacnephia aguirrei had at least three generations in a year.

Rearing black flies (Diptera: Simuliidae) in the laboratory: bionomics and life table statistics for Simulium pictipes.

Mass-rearing techniques were used to rear Simulium pictipes through 3 generations. Survival from early larva to adult (parental generation) ranged from 74.1 to 94.7%, while subsequent generations (F1 and F2) exhibited survival rates of 64.9–94.8% from egg to adult. As many as 11,295 vigorous adults were obtained from a single rearing. Mating occurred at a low rate, and no selection for increased insemination was observed within 3 generations. However, females readily blood fed through membranes and large numbers of eggs were laid routinely. Comparisons are drawn between S. pictipes and other black fly species exhibiting similar patterns of larval and adult behavior, such as members of the S. damnosum complex.

Seasonal occurrence of, development of, and the influences of selected environmental factors on the larvae of Prosimulium and Simulium species of blackflies (Diptera: Simuliidae) found in the rivers of southwestern Alberta

Larval development of Simulium arcticum Malloch (IIL-3), S. defoliarti Stone and Peterson (IIS-14.15), and S. tuberosum Lundström (FG) was documented for four rivers in southwestern Alberta from 1982 to 1984. Simulium arcticum (IIL-3) and S. tuberosum (FG) had seven instars; these two species were multivoltine with two or three generations per year, while S. defoliarti (IIS-14.15) was univoltine. Water temperature, river discharge, and turbidity were the only environmental factors of five parameters measured that were significantly correlated with the seasonal development of larvae of S. arcticum (IIL-3), S. defoliarti (IIS-14.15), S. vittatum Zetterstedt complex, S. tuberosum (FG), and Prosimulium onychodactylum Dyar and Shannon complex. Also, we speculate on the effect that food quality and quantity have on larval growth and development of blackfly species that breed in mountain rivers.

Transmission of Leucocytozoon smithi (Sporozoa: Leucocytozoidae) by black flies (Diptera: Simuliidae) in New York, USA.

Field and laboratory studies were conducted during 1981 and 1982 to analyze seasonal patterns of Leucocytozoon smithi transmission to sentinel turkeys in New York, USA, and to identify the black-fly vectors of this parasite. Elevated and nonelevated domestic sentinel turkeys were posted every 2 wk in the summer of 1981, and infections were monitored via Giemsa-stained smears of peripheral blood. Black-fly catches were made near the sentinels using modified CDC traps and sweep-netting. Experimental infections of black flies were obtained by direct feeding on infected turkeys or by feeding flies on infected blood through natural and artificial membranes. Infections were transferred to turkeys via intraperitoneal inoculation of black-fly suspensions. Transmission of L. smithi began in late June 1981 and persisted until late September. Eight species of black flies were collected at the field site, but over 95% of those collected from CDC traps near the sentinels were Simulium aureum . A total of 12 of 232 S. aureum females dissected in 1981 and 25 of 199 in 1982 had Leucocytozoon spp. sporozoites in their salivary glands. Leucocytozoon smithi sporozoites were produced experimentally in S. aureum, S. jenningsi, S. vittatum , and S. pictipes . Two complete transmission cycles of L. smithi were accomplished in the laboratory using colonized S. vittatum females as experimental vectors.