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Nuku-Hiva and Eiao are the only islands of the Marquesas archipelago where blackflies bite humans. Knowledge of the geographic distribution of species is necessary to optimize control operations. Looking at frequency distributions of labral fan rays numbers from a large sample of larvae allowed redefinition of species. Simulium sechani Craig & Fossati, 1995, become the only species represented in Eiao. This species live in Nuku-Hiva too, but is limited to the external part of the main caldera. Presence of S. buissoni Roubaud, 1906, in all part of the island is confirmed, as is presence of S. hukaense Séchan, 1983 but in reduced number. Large samples of S. sechani extends its labral fan rays numbers. Stability of the described repartition over several decades is shown.
Simulium sechani Craig & Fossati, 1995 was recently found for the first time in a part of Nuku-Hiva Island. This species coexists with Simulim buissoni Roubaud 1906, the dominant species, and always regarded as the main biting fly on the island. The problem is that optimisation of control operations needs a good knowledge of targets. The unknown female of S. sechani is the reason of this study. This study used samples collected before the description of S. sechani to try to correlate its geographical extent with easy to use biometrical parameters, and then give a first look at the possibilities of determination of adult females. Parameters used are: the numbers of maxillary and mandibular teeth, the dimension of the third antenna article and the number of apical hairs, the width and depth of the ventral plate space, and the number of hairs on the radial vein of the wing. Analysis of frequency distributions in relation with sampling sites and trapping hosts did not allow us to find convenient diagnosis characters, but contributed to new questions about isolation of insect populations in valleys and hosts usually used.
Two anthropophilic species are known from the Marquesas archipelago (French Polynesia): Simulium buissoni Roubaud, 1906 and S. sechani Craig & Fossati, 1995. The need to control them requires good knowledge about their larval growth, larvae being the only stage actually susceptible to control. A biometric study based on cephalic measures of the two species, shows that they both have seven larval instars. Size variations following species and sampling sites are examined, as are variations of the sex of the two last larval instars. A recolonization experiment, after treatment of a part of a river, allows us to quantify larval growing length of S. buissoni, which is about 12 days. These data allow us to determine the optimal treatment frequency.
High density of haematophagous blackflies on Nuku-Hiva Island (Marquesas archipelago, French Polynesia) is a handicap to its optimal development. The present study contains observations from many sampling sites to examine aggressive periods of Simulium buissoni Roubaud, 1906. Density of aggressive females is very high, principally in highly irrigated sites of the island. Biting rates show low variation between days, and a diurnal activity, with a poorly pronounced circum-meridian maximum. Parity rates show great variation between sampling stations, but are lowest during the day. A hypothesis of greater spatial dispersion of nulliparous females allows explanation of much of the observed variation. Sampling in and out of a house shows exophily of blackflies. Proportion of parous females is greater in the house. Data collected over a long period show that earlier densities were greater than recent ones. Perturbation of the environment is probably the basis of this decrease.
Several Simulium species were investigated as to their biting habits and natural infections with filarial larvae at Ban Pan Fan, Chiang Mai Province, in northern Thailand. Female adults flies landing on or flighting around a human and a water buffalo were collected during the daytime from 06.00 to 19.00 hours on 22 June 2001. As a result, 217 S. nodosum, 86 S. asakoae and two S. nigrogilvum were obtained from a human attractant, and 416 S. nodosum, 25 S. nakhonense, 16 S. asakoae, four S. fenestratum and two S. nigrogilvum, from a water buffalo. The blood-feeding was confirmed only for S. nodosum and S. nigrogilvum on humans, and for S. nodosum and S. nakhonense on water buffalos. Dissections of these simuliids showed that S. nodosum was naturally infected with developing filarial larvae. Two types of microfilariae were distinguished but only one type of infective larvae. These larvae resembled Onchocerca suzukii, a parasite from a wild Japanese bovid, suggesting that an unknown Onchocerca species from ruminants was transmitted in Thailand. Infection rates with all stages of larvae and third-stage larvae were 2.3% (14/608) and 1.0% (6/608), respectively. This is the first report of natural infections of black flies with Onchocerca larvae in Southeast Asia, and the involved black fly species is shown to be not only anthropophilic but also zoophilic in this region.
Cytotaxonomic analysis of the polytene chromosomes from larvae of the Simulium damnosum Theobald complex from the island of Bioko in Equatorial Guinea is reported, and a new endemic cytoform is described. Chromosomally this cytoform is close to both S. squamosum (Enderlein) and S. yahense Vajime & Dunbar, but is not identical to either. However, it is morphologically and enzymatically identical to S. yahense. The Bioko form was also found to differ from other cytoforms of the S. damnosum complex in West Africa in the copy number or RFLP pattern of several different repetitive DNA sequences. It is clear that the Bioko form is genetically distinct from other populations of the S. damnosum complex, and whilst it is closest to S. yahense, it shows features that suggest a high degree of geographical and genetic isolation. Such isolation is an important consideration in the assessment of the potential for onchocerciasis vector eradication on Bioko.
Larvae of the Simulium damnosum complex were collected in southern Malawi, in particular from the Thyolo onchocerciasis focus. Cytological identifications revealed the occurrence of S. (Edwardsellum) thyolense sp.nov., S. kilibanum Gouteux, 'Ketaketa', a new cytoform tentatively designated 'Mwamphanzi', and two unassigned specimens. Simulium thyolense sp.nov. is presumably the major vector of Onchocerca volvulus in the area, but it remains possible that the other cytospecies are secondary vectors. Simulium thyolense sp.nov. is most appropriately classified near the 'Sanje' subcomplex, whereas 'Mwamphanzi' and the unassigned specimens are members of the 'Ketaketa' subcomplex.
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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.
Previous studies on the morphological identification of adult female Simulium damnosum s.l. have involved use of colour characters. To determine the degree to which these qualitative characters are influenced by the physical environment, a portable rearing system was constructed. Wild-caught female flies and flies emerging from pupae maintained at ambient temperatures or above showed entirely pale antennae, fore-coxae, wing-tufts and hairs on the scutellum and ninth abdominal tergite, as is normal for S. sirbanum. Adults reared from larvae at below ambient temperatures were also pale, except for the antennae which were dark in all specimens. Adult females emerging from pupae maintained at below ambient temperatures were entirely pale up to the fourth day of emergence and mostly with dark antennae. The biological significance and the implications to the morphological identification of the savannah species of the S. damnosum complex in West Africa are discussed.
Adult female Simulium damnosum s.l. flies obtained in nine countries of the Onchocerciasis Control Programme were examined for 14 morphological characters with the aim of selecting specific characters to identify the main species that form the complex. Two approaches were used, the first involved discriminant function analysis of the species groups using all the characters which were both qualitative (the colour of the fore coxa, the antennae, the wing tuft, the arculus, the ninth abdominal tergite setae and the scutellar setae) and quantitative (the lengths of thorax, antenna, and femur, tibia and first basitarsus of both the fore and hind legs) in nature. The second sought colour characters unique to the S. damnosum subcomplex and to S. yahense, to separate them from the rest, and progressively applied discriminant analyses in the dichotomous stepwise manner to within the subcomplex level. The combination of pale arculus and pale antennae with pale or dark fore coxae were unique to the S. damnosum subcomplex, whilst those of black arculus together with wholly dark or mixed ninth abdominal tergite setae and scutellar setae were unique to S. yahense. Further discrimination was achieved between subcomplexes and species by entering the qualitative and quantitative characters into discriminant function analysis. The two schemes were both successful at separating the main species subcomplexes of the S. damnosum complex, with 90-100% correct classification. Within the subcomplex level, correct identification of sibling species was 85-100% successful.(ABSTRACT TRUNCATED AT 250 WORDS)
Experimental infections of Simulium metallicum s.l. with Onchocerca volvulus were carried out in two onchocerciasis foci, Altamira and Trincheras, in northern Venezuela, to determine vector competence. Wild-caught flies, fed on infected volunteers, were maintained in the laboratory for 13-15 days at 27 degrees C. Parasite development was complete but asynchronous and retarded. No differences in the vector competence of the two populations of S. metallicum s.l. were found. However, a less efficient development of the parasite occurred during the dry season at both localities. The distribution of the parasite within the vector was aggregated and also displayed seasonal variation. The seasonal susceptibility may be a consequence of a density-dependence regulation mechanism of the parasite within the vector. These results indicate a relatively low vector competence for S. metallicum s.l. in northern Venezuela.
Morphometric multivariate analyses were carried out in order to separate the females of the closely related anthropophilic and non-anthropophilic members of the Simulium damnosum s.l. complex occurring in western Uganda. Simulium kilibanum (= 'Nyamagasani'), 'Nkusi', 'Sebwe' and S. pandanophilum were compared with the West African S. damnosum subcomplex, S. soubrense and S. yahense to correlate the results with those of previous studies. Simulium pandanophilum could be clearly discriminated. However, only 72%-88% of identifications among the closely related S. kilibanum, 'Sebwe' and 'Nkusi', which all belong to the 'Sanje' subcomplex, were correct. The two forest species S. soubrense and S. yahense slightly overlapped but were distinct from all others.
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The life cycle of Simulium jenningsi Malloch was compared at two study sites representing the largest and smallest streams (New River and Indian Creek, respectively) where this species is known to breed in southern West Virginia. Larvae first appeared in March, and the first generation emerged in April, followed by two to four more generations by September. A few larvae and adults persisted in autumn, then the population overwintered in the egg stage. There were considerable differences in life cycle at the two study sites. In the New River, emergence of the first generation was 2-3 wk earlier, there were five generations rather than three, and the last larvae of the season persisted 1 mo later as compared with Indian Creek. Warmer temperature and higher quality food in the New River are probable explanations for differences in life cycle. Effective pest management of this species will require larviciding at frequent intervals (1-2 wk) from April through September in many streams over a broad geographic area because of the species' nonsynchronous life cycle, occurrence in different size streams, and strong dispersal ability.