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A closed system of water circulation previously devised for rearing nearctic black flies was used for two cohorts of Simulium damnosum s.l. (Ghana strain). Complete generation development from field-collected eggs occurred in both instances with the production of F1 adults and F1 pupae respectively. Survival of larvae form the 3rd instar to pupation was extremely high for both parental and filial generations and ranged form 63-98%. In 3 of the 4 rearings (1P, 2P, 1F1), pupal survival ranged form 98-100%. Mating attempts were frequently seen but insemination rates were low (greater than 1%). Nulliparous females were anthropophilic and exhibited bloodfeeding rates ranging form 67.5-87.5%. Parous females also readily engorged on humans. Porcine and rabbit hosts proved less attractive while two membrane systems (Baudruche, chicken skin)using equine, bovine, or chicken blood elicited practically no engorgement. Gravid females readily deposited fertile and infertile eggs in an oviposition chamber designed originally for Simulium decorum.
Onchocerca tarsicola is a subcutaneous filariid of the red deer living on the tendons of the radial-carpal and tibial-tarsal joints. Its microfilariae concentrate mainly in the external ears. The extrinsic cycle of this parasite was investigated. In a hyperendemic area wild-caught Odagmia ornata were dissected, as well as samples which had fed on a tame deer and been kept in the laboratory after the infecting blood-meal. About 3 to 5% of the flies were infected with larval stages of Onchocerca tarsicola. More than 40% of Odagmia ornata induced to feed on the ears of the deer became infected and about 30% of the flies which survived more than 18 days contained third-stage larvae. The larval development in the vector is described. Prosimulium nigripes appears to be a second natural vector of Onchocerca tarsicola. Observations concerning the potential vectors of O. flexuosa, O. tubingensis and Cutifilaria wenki living in red deer are discussed.
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The purpose of this paper is to provide a relatively simple means for recognizing the six main vector species or species groups of the Simulium damnosum Theobald complex that can be distinguished primarily to assist non-specialists, technicians and field personnel who have to handle many specimens in a relatively short period of time.
A technique was developed for estimating the relative age of field-collected females of the Simulium damnosum complex. Females were allowed the opportunity to blood-feed while attacking and held 48 hours to permit partial maturation of the ovaries. The ovaries were then dissected out and the number of maturing oocytes was counted. Nullipars were easily identified by their lack of follicular relics. The remaining parous females generally fell into one of four groups depending on their egg counts. Wihout a laboratory colony for specific reference it is presently impossible to confirm that the fecundity groups represent successive gonotrophic cycles. Nevertheless, there is little doubt that the data demonstrate a decreasing level of fecundity in flies of advancing age thus allowing direct comparisons to be made between different populations. The epidemiological significance of this is discussed.
A method of rearing large numbers of black flies has been devised using a closed system of water circulation. The subsystems used for hatching, feeding, filtration, and adult trapping are labor-efficient and sufficiently flexible to be useful for rearing most species of temperate and tropical black flies. The filtration subsystem permits a daily assessment of such parameters as larval growth rate, drift, and mortality so that life table statistics can be derived for populations of immatures. Four species of black flies, Simulium pictipes, S. vittatum, S. decorum, and Cnephia dacotensis, were used in developing this unique rearing system. Percentage survival varied with species and appeared to be a function of food quantity within discrete particle-size intervals. Over 28,000 larvae of C. dacotensis were reared in a single unit with 89.3% surviving to the adult stage. In each of two rearings of S. pictipes, conducted under different nutritional regimens, approximately 60% survived to the imaginal stage. Over 9,500 adults of S. vittatum were reared from 12,127 eggs. An F1 generation of S. decorum was produced from parental stock that originated as field-collected larvae. Combined survivorship of this species approached 94% with the production of 5,847 adults.
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An blood/membrane apparatus was used to study the feeding responses of field-collected and lab-reared Simulium vittatum and Prosimulium mixtum. Both species showed preferences for human, horse, cow and pig bloods while neither fed in high rates on dog or goose bloods. These results are discussed in the context of field data on host preferences. Size was shown to be related to the feeding rates in S. vittatum, larger flies feeding more readily. Lab-reared S. vittatum females fed in decreasing rates over 1-8 days after emergence. This is believed to be related to the autogenous maturation of the ovaries in this species.
The fecundity of autogenous Simulium vittatum and Prosimulium mixtum females was shown to be related to the size of the female which in turn was a result of the quantity of food provided to the larvae. Among females of equal size, sucrose allowed a greater expression of autogeny compared to females given only water. In the case of lab-reared S. Vittatum, a blood-meal enhanced autogenous egg production when females were fed within 24 h after emergence. Preliminary data indicated that for P. mixtum human blood stimulated a greater number of ovarioles to begin maturing compared to avian blood. Evidence was produced which demonstrated a clear decline in fecundity over consecutive gonotrophic cycles for both S. vittatum and P. mixtum.
In small streams of Donbass on pupae of black flies Odagmia ornata Mg. and Chelocnetha angustitarse Lundstr. occur the larvae of water mites Sperchon setiger S. Thor. and Sperchonopsis sp. n. which pass from pupae to imago during the emergence. The infection extensiveness of adult black flies amounted on the average to 18--20% and intensiveness-- to 1--7 larvae. Larvae of water mites were not recorded from pupae and imago of Simulium argyreatum Mg. and of the genus Wilhelmia. Under laboratory conditions parasitism of water mites larvae on hungry adult black flies caused their quicker death (8--22 hours) as compared to noninfected individuals (1 to 2 days).
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Polymorphisms for the presence or absence of supernumerary bands, for band size, nucleolar expression and the location of secondary nucleolar organisers found in the polytene chromosomes of Simulium ornatipes are described. In all the seven band polymorphisms analysed, six of which involve single bands and one a multiple band complex (IILH), phylogenetic evidence shows that there has been an addition of material. IILH consists of seven amplified C-bands, two supernumerary C-bands and a supernumerary segment involving two C-bands and an interband region. These bands are linked to the peracentric inversion IIL-3, five of the bands being located only within inverted segments. Comparison with mitotic chromosomes suggests that IILH heterochromatin is not under replicated in polytene chromosomes. Recombination between IILH components occurs at a very low level which is insufficient to disrupt the integrity of the polymorphism. It is concluded therefore that the complex evolved in a sequential series, the origin of IIL-3 being the first step. Single band polymorphisms, some of which are also linked to inversions, show similar heterochromatic properties to the IILH bands. A mechanism of selective DNA sequence amplification is proposed to explain increase in band size and the accompanying heterochromatinization. Most supernumerary bands may be amplifications of submicroscopic bands. Nucleolar organisers show heteromorphism for expression and rare secondary nucleoli are found on all chromosomes. It is argued that a multiplicity of sites for ribosomal genes are distributed in the genome and that selective sequence amplification, similar to that proposed above, can increase these sequences to a functional level at any of the sites. This would explain the lability of nucleolar sites in different blackfly species.
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Three techniques for sampling larvae of Simulium damnosum in different water depths are described. Preliminary results prove that the larvae can settle much deeper, i.e. up to 3 m, than reported before (0-30 cm). Without impairment pupation takes place in any depth.
A stereoscan electron microscopy study of two forms of Simulium of Kivu, Zaire, apparently belonging to the Simulium damnosum complex, revealed some morphological particularities: the presence of microvillosities on the enormously enlarged scales of a larval form from a western tributary of lake Tanganyika, and the presence of spine-combs and comb-shaped scales on the nymphal cuticle of this form and a form from the equatorial rain forest of Irangi.