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The population from Kirghizia (the Tokailu river) does not differ from others by the variability rate of its morphological characters but its karyotypical characters (homozygous inversion in chromosome III and additional B-chromosomes) suggest a genetic isolation of this population in the system of the species.
Natural hybridisation between Simulium sanctipauli (sensu Quillevéré et al. 1981) and Simulium squamosum/yahense occurs at a rate of around 0.001. A single larva has been found which is unambiguously a backcross between S. sanctipauli s.l. and a S. sanctipauli s.l. X squamosum/yahense hybrid. This discovery indicates the possibility of genetic introgression between these species. Examination of the polytene chromosomes of this backcross progeny and subsequent re-examination of the type specimens has led to the remapping of fixed interspecific inversions in chromosome arm 1L.
Two species of Simulium were used to examine the effect of experimental Onchocerca lienalis infections on their fecundity and oviposition rates. S. ornatum s.l. was chosen as a natural vector of bovine onchocerciasis in Britain, and S. lineatum was selected because of its suitability as an experimental model for oviposition studies. Infection was either by feeding with blood containing microfilariae, or by intrathoracic injection of the parasites. Using the blood feeding technique, reductions in the fecundity of S. lineatum were observed at rates of 21 to 76%, depending on the concentration of parasites. A reduction of 21% in the fecundity of S. ornatum s.l. (P less than 0.05) was achieved when flies were fed on microfilariae at 69,000 per ml. Although individual flies feeding on infected blood may take as much as those in control groups, the feeding rates were reduced in several instances. S. lineatum also showed a depression of oviposition rate when infected by O. linenalis larvae. Fecundity was also significantly reduced when the route of infection was intrathoracic. Reductions for S. lineatum depended on the inoculum, but were either 36% (10 microfilariae per fly) or 54% (50 microfilariae per fly). S. ornatum s.l. showed a 13% reduction in fecundity when given 20 microfilariae per fly. It was concluded that similar experimental studies could be usefully performed with S. damnosum s.l. infected with O. volvulus microfilariae.
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A ten-point visual method of estimating the abundance of immature blackflies in the field is proposed and tested. The method is based on the comparison of larvae and pupae found on natural substrates, with ten diagrammatically prepared abundance classes. When estimates were based on the abundance of blackflies within a 4 x 4 cm area of highest density, there were no significant differences between estimates based on the ten-point visual method and those based on actual counts (P > 0.05). The time taken to assess the abundance of larval blackflies on 30 substrates was about 15 min, depending on substrate accessibility. Personal bias was assessed independently by four people, and was negligible when estimates were based on the highest densities within a 4 x 4 cm quadrat. The method tends to overlook very small larvae, and is not recommended for estimating overall population densities. However, the method provides a reliable, practical and rapid index of blackfly abundance suitable for use in blackfly control programmes.
Laboratory bioassays evaluated the pathogenicity of the entomopathogenic fungus Tolypocladium cylindrosporum against Aedes triseriatus. All larval instars were found to be susceptible at temperatures from 18 to 25 degrees C. Blastoconidia were more virulent than conidia. Mortality was proportional to exposure time in assays using blastoconidia. Blastoconidia and exposure time appear to be a more adequate method for bioassay of T. cylindrosporum virulence than the standard procedure of using conidia and continuous exposure. Tolypocladium cylindrosporum was also active against Simulium vittatum black fly larvae, but the mortality recorded was much lower than with mosquito larvae.
Twenty-nine Simulium species were recorded in the Republic of Guinea. The geographical distribution of the blackfly species in its areas is shown in the paper. The most probable vector of Onchocerca volvulus are S. damnosum s. str and S. sirbanum which predominate in the landscapes of Sudan and Guinea savannas. S. yahense, S. soubrense, and S. sanctipauli are likely to be vectors in the forest-savannas and tropical rain forests.
Of 176 black fly females collected resting at the edge of El Rosario River, 77% were caught in rocky shelters, whereas the others were captured on damp stretches of river bank. Simulium ochraceum predominated in the catches (74%), followed by Simulium metallicum (21%), and Simulium callidum (5%). Percentages of females without blood in their gut were 70, 85, and 67%, respectively. Of 55 S. ochraceum females that had recently oviposited (sacculate), 29 had the remains of a blood meal in the gut. Of 64 nulliparous females, 48 exhibited early oogenesis (Christopher's stage I-II) indicating recent emergence. At Las Golondrinas village, 36% (71) of 199 specimens were S. ochraceum, of these 85% had no blood in the midgut. Five females of S. ochraceum at this locality had red blood and 6 had black blood in their gut. Of 43 parous and 28 nulliparous females, 36 and 25 had ovaries at stages I-II, respectively. Most females of S. metallicum had no blood in their gut (92%). Nullipars were abundant (91) and stage N (24 h old) was observed in 66 of them.
Simple techniques are described for collecting black fly pupae from streams using plastic strips and for rearing large numbers of adult black flies in inexpensive enclosures made of chicken wire and cloth mesh netting, and 2 methods are described for rearing adult black flies individually from pupae. The first method of rearing individual black flies uses 1.5-ml microcentrifuge tubules and the second uses easy-to-construct rearing chambers that provide moisture for the developing pupa and water for the adult to imbibe. Instructions for assembly are provided. Specimens obtained using these rearing chambers are of museum quality.
A suspended-net technique was used to capture blackflies attracted to and engorging on Dorper and Merino sheep on irrigated pastures. Two bait animals of each breed were restrained individually in wire-mesh enclosures located within four larger pens, each containing nine more animals of the same breed. Nets were suspended partly over the restrained animals and blackflies were collected at the end of 2-hour or longer periods. Mean numbers of blackflies captured in association with Merino (73.3/h) and Dorper sheep (89.1/h) did not differ significantly. Numbers of captured blackflies correlated (rho = 0.8361) with levels of irritation shown by sheep. Engorgement on Merinos was significantly (p = 0.009) higher than on Dorpers. Percentage engorgement was low, mostly below 10% on Merinos and below 5% on Dorpers. When high wind speeds and high saturation deficits (associated with temperatures in the mid-thirties) occurred, the success of capture was impaired. The technique is useful for quantifying the abundance of irritating blackflies in the immediate proximity of smallstock under experimental conditions.
Carbon dioxide and 1-octen-3-ol were evaluated individually and in combination as black fly attractants. Significantly greater numbers of Cnephia pecuarum were collected in traps baited with CO2 and CO2 + octenol as compared with octenol alone or no bait. While greater numbers of C. pecuarum were collected in traps baited with the combination of CO2 and octenol as opposed to CO2 alone, results were only significantly different (P > or = 0.05) in one test. In contrast, significantly (P > or = 0.05) more adults of Simulium meridionale were collected in traps baited with CO2 alone. Octenol alone was not an effective attractant for the black fly species collected in the course of this study. In addition, use of octenol in conjunction with CO2 may impair representative sampling of black fly species present in a given area.
Larvae of 4 species of black flies, Prosimulium mixtum, Simulium vittatum, S. decorum and Stegopterna mutata, were exposed in the laboratory to cercariae of the digenean Plagiorchis noblei in flowing water. Prevalence and intensity of infection of all species varied directly with exposure intensity and decreased with increasing water velocity; prevalence increased with larval size. Infection levels for P. mixtum were higher than for the 3 other species. Mortality among infected larvae of all species was 3 times that of controls. Exposure of black fly larvae to P. noblei cercariae may adversely affect their survival.
The gonotrophic cycle, survivorship, and daily parity rate of Simulium ochraceum were estimated from specimens collected during routine vector surveillance in southern Mexico, using a vertical (time-specific) method. Series of sequential data analysis on parity of the entomological data obtained in February 1994 showed the highest significant (P < 0.05 alpha) correlation indices (r = 0.63 and r = 0.67) for a 4-day time lag, indicating that the mean gonotrophic cycle length corresponded to 4 days. Daily survival rate was estimated to be 0.80, the survival to infective age (12 days) to be 6.9%, and the daily parity rate to be 0.41. These estimations are in accordance with those previously obtained by others from mark-release-recapture experiments (horizontal method) in Guatemala.
Data from several operational black fly abatement programs using Bacillus thuringiensis var. israelensis (B.t.i.) in New York State's Adirondack Mountains were analyzed to determine what the concentration of formulation in the stream might have been if application rates were determined by a stream's width rather than its discharge. There was a high correlation (magnitude of R = 0.87) between discharge and width measured at 315 treatment sites. Had the applications been based upon the stream width, 96% of the actual concentrations in the streams would have been within plus or minus a factor of 5 and none exceeding a factor of 10, a range in which B.t.i. remains environmentally safe and effective.
Karyotypes of four species of blackflies belonging to plesiomorphic superspecific taxa, Prosimulium pronevitshae, P. frontatum, Stegopterna richteri, Greniera dogieli have been studied. Structural peculiarities of polythene chromosomes of the salivary glands in older larvae have been analysed. Banding patterns of polythene chromosomes and descriptions of these karyotypes are given for the first time. Karyotypic features of the examined species are compared. Based on the comparative karyological analysis the differences between taxa and their possible relationships are revealed.
A new species of blackflies, Montisimulium peskovi sp. n. from the northern Tien Shan (Kazakhstan Republic) is described. Morphological characters of development phases are given. The photo maps of the salivary polythene chromosomes are constructed.
Eleven morphometric and four qualitative features of larvae, as well as 6 morphometric parameters of pupae of Odagmia caucasica, which had been collected in 5 geographically remote regions of Armenia, have been studied. In this work besides absolute values of features we have used their ratios (indices) that shows forms and proportions of different organs. It was found, that larvae taken from Bzhni and Getashen had asymmetry of bilateral characteristics and that there were differences in the level of morphometric features variability; the latter fact is connected with sex and phase of the insect. Study of chronological variability of populations from Bzhni, Getashen and Martuni has revealed differences in the nature of distribution of features. It was shown that the rate of differentiation between geographically isolated populations fluctuated in the range from 20 (Getashen) to 33% (Amassiya). Differences in the qualitative alternative features and in the rate of microsporidium infection distinguish the differentiation of populations from Bzhni and Amassiya, which is caused by anthropogenic factor in Bzhni and by isolating landscape barrier in Amassiya. Species-specific morphometric features were discovered; these were the indices of proportions of larva ventral sclerite and of pupa respiratory filaments.
Some changes in the synonymy of several generic names are given (Ahaimophaga Chubareva, 1978 = Helodon Enderlein, 1921; Haimophaga Rubzov et Yankovsky, 1984 = Helodon, Enderlein, 1921; Astega Enderlein, 1930 = Cnephia Enderlein, 1921; Boreosimulium Rubsov et Yankovsky, 1982 = Hellichiella Rivosecchi et Cardinali, 1975; Odagmia Enderlein, 1921 = Simulium Latreille, 1802; Gnus Rubsov, 1940 = Simulium Latreille, 1802). For 18 preoccupied species names (junior homonyms) the new replacing names are proposed (alajensis Rubzov. 1972 = dubitskii. nom. n.: bicorne Dumbleton, 1973 = crosbyi, nom. n.; borealis Malloch, 1919 = arctocanadensis, nom. n.; chelevini Ivashchenko, 1978 = ivashchenkoi, nom. n.; decafile Rubzov, 1976 = decafiliatum, nom. n.; frontatus Yankovsky, 1982 = boreopacificus, nom. n.; fulvipes Ono, 1978 = onoi, nom. n.; fuscum Rubzov, 1963 = fuscatum, nom. n.; hibernale Rubsov, 1967 = lugense, nom. n.; intermedia Rubzov, 1956 = orenburgica, nom. n.; jacuticum, Rubzov, 1973 = tiksiense, nom. n.; kamtshaticum Rubzov, 1940 = kamtshadalicum, nom. n.; latitarsus Rubzov, 1971 = mongolense, nom. n.; minutum Rubzov, 1959 = minuticorpus, nom. n.; rheophilum Tan et Chow, 1976 = tanetchowi, nom. n.; sedecimfistulata Rubzov, 1976 = dzhungarica, nom. n.; septentrionale Tan et Chow, 1976 = chowettani, nom. n.; tenuitarsus Rubzov, 1969 = chovdica, nom. n.).