Culicoides Populations Research Articles

The oral susceptibility of South African field populations of Culicoides to African horse sickness virus

Twenty-two isolates of African horse sickness virus (AHSV), representing its distinct serotypes, geographical and historical origins, were fed to three populations of South African livestock-associated Culicoides spp. (Diptera, Ceratopogonidae). Infective blood meals included 12 recent isolates, nine historical reference strains and one live attenuated vaccine strain serotype 7 (AHSV-7) of the virus. Field-collected midges were fed through a chicken-skin membrane on sheep blood spiked with one of the viruses, which concentrations ranged from 5.4 to 8.8 log(10)TCID(50)/mL of blood. After 10 days incubation at 23.5 degrees C, AHSV was isolated from 11 Culicoides species. Standard in vitro passaging of AHSV-7, used for the preparation of live attenuated vaccine, did not reduce its ability to infect Culicoides species. Virus recovery rates in orally infected Culicoides midges differed significantly between species and populations, serotypes, isolates and seasons. Significant variations in oral susceptibility recorded in this study emphasize a complex inter-relationship between virus and vector, which is further influenced by multiple intrinsic and extrinsic factors. As it is not possible to standardize all these factors under laboratory conditions, conclusive assessment of the role of field-collected Culicoides midges in the transmission of orbiviruses remains problematic. Nevertheless, results of this study suggest the potential for multi-vector transmission of AHSV virus in South Africa.

An investigation on the Culicoides species composition at seven sites in southern Switzerland

In the past decade, there have been regular outbreaks of bluetongue (BT) in many parts of Europe. Owing to the presence of BT disease and its vectors in countries adjacent to Switzerland, an initial entomological survey was conducted in 2003, which established the presence of several midges of the genus Culicoides (Diptera: Ceratopogonidae). Subsequently, a sentinel herd monitoring system was established with the primary entomological aim being the determination and further study of Culicoides population compositions. Insects were collected in 2005 and 2006 at seven sentinel herd sites in the south of Switzerland (canton of Ticino) near the border of Italy, using Onderstepoort-type light traps. This region is botanically and zoologically similar to the Mediterranean and is one of the warmest and most humid areas of the country, hence it is considered a potential access path for BT disease into Switzerland. Collections were made at four cattle farms, two equestrian centres and one goat farm. Sites were sampled four times per month from June to October. Traps were operated from dusk until dawn and samples were collected monthly for analysis through microscopy as well as a Culicoides imicola-specific PCR. Results confirmed the absence of C. imicola (Kieffer) and demonstrated that the potential BT virus vectors are highly abundant, notably: Culicoides obsoletus (Meigen), Culicoides scoticus (Downes & Kettle) and Culicoides dewulfi (Goetghebuer) subgenus Avaritia and Culicoides pulicaris (Linnaeus) subgenus Culicoides. These findings expand the current knowledge of Culicoides population composition in the southern part of the Switzerland. Culicoides cataneii (Clastrier), Culicoides flavipulicaris (Dzhafarov), Culicoides indistinctus (Khalaf), Culicoides nubeculosus (Meigen) and species of the Grisescens complex were reported for the first time in Switzerland.

Test de sensibilité de l'Organisation mondiale de la santé appliqué aux Culicoides : présentation d'un essai multicentrique

The aim of this work is to organize a multicentric assay to com­pare susceptibilities of Culicoides populations to insecticides (i.e. C. imicola and C. obsoletus sensu stricto). The base line of the World Health Organisation test kit (WHO/VBC81.805) is to expose mosquitoes to papers impregnated with insecticides to detect the resistance of Anopheles (paludism vector) in the field. In a novel approach, the WHO test can be used on Culicoides to assess midges’ susceptibility to insecticides. Information on the intrinsic susceptibilities to insecticides is required to assess correctly the existing (or new) formulations of insecticide. This multicentric assay will improve our capacity to experiment by networking and assess the population variability by comparing susceptibilities between different populations of Culicoides. Field-collected midges are trapped alive using an ultraviolet light trap (OVI model, South Africa) and replacing the collection jar with a fine mesh cage. To prevent desiccation, cages are covered with wet papers, wrapped in aluminium foil and retrieved at dawn. It is important to choose the site and period with abun­dant target species to improve robustness with more individuals. Experiments should be carried out in an insecticide-free environ­ment with constant temperature and humidity, and started a few hours after collection. Insecticide-impregnated papers are rolled and fastened into the WHO kit test tube. About 30 Culicoides (approximately 20 nulliparous females) are collected and trans­ferred to the tube. Tubes are maintained horizontally for an hour (exposure to insecticide). Mortalities are recorded 1 h and 24 h after exposure. One control is performed without insecticide to validate the test. Mortalities are analysed by probit regression to obtain LC50 and LC90 for each population. The test has to be run at least with four concentrations of insecticide, one con­trol and four replicates with samples from the same population. Only nulliparous females are recorded. Insecticide concentra­tions are given in percentages (WHO standard). In this WHO test, the target species are C. imicola and C. obsoletus s.s., and the active ingredient used is deltamethrin at doses 0.005, 0.001, 0.0005 and 0.0001%. Data will be centralized and analysed by EID-Méditerranée (France), and results will be given back to the partners and published. Future studies could focus on comparing the four deltamethrin concentrations on other species and testing Culicoides susceptibility to other components.

Interactions vecteurs-virus : diversité des sérotypes et des souches de la peste équine africaine, et populations géographiques

The most abundant Culicoides species in an area is not inevi­tably the most competent vector species for a specific virus. Oral susceptibility, as an indicator of vector competence, is a measure of the portion of vectors taking a blood meal from an infected host that actually becomes infective. Cumulative laboratory oral susceptibility results from South Africa indicate a multivector potential for bluetongue virus (BTV) as well as for African horse sickness virus (AHSV). Considering the unique biology of potential vector competent Culicoides species one can appreciate the complex epidemiology of these diseases. The oral susceptibly of C. imicola, a proven vector of AHSV and BTV, was relatively low for most of the viral isolates and even appeared to be refractory to infection with some of the isolates used. This relatively low oral susceptibility may partly explain the low field infection prevalence of AHSV and BTV recorded in field collected midges. In South Africa, the relatively low oral susceptibility as determined for some of the isolates is easily compensated for by the high abundance of C. imicola. Differences found in the virus recovery rates of various AHSV serotypes/isolates from the various Culicoides species and even different populations of the same species emphasize the fact that, although oral susceptibility tests provide important information about a specific vector population, it provides no predictability about the behaviour of other populations with different strains of virus. Differences found in the oral susceptibility of C. imi­cola and C. bolitinos for isolates of the same serotypes of AHSV suggest coadaptation between orbiviruses and vectors present in a given locality. Real-time monitoring of vector competence might be difficult as it would require assessing local Culicoides populations using variants of orbiviruses currently in circula­tion. It needs to be emphasized that laboratory demonstration of oral susceptibility is not the only necessary step to implement a competent vector. It is, however, an indication of the ability of a vector to support virus replication and one of the critical components of vectorial capacity. Vector capacity is the relative measure of a vector population to transmit a virus to a vertebrate population. In addition to vector competence, vectorial capacity depends on the biting rate, host selection, vector survivorship, and the extrinsic incubation period of the virus.

The phenology and population dynamics of Culicoides spp. in different ecosystems in The Netherlands

The Netherlands has enjoyed a relatively free state of vector-borne diseases of economic importance for more than one century. Emerging infectious diseases may change this situation, threatening the health of humans, domestic livestock and wildlife. In order to be prepared for the potential outbreak of vector-borne diseases, a study was undertaken to investigate the distribution and seasonal dynamics of candidate vectors of infectious diseases with emphasis on bluetongue vectors ( Culicoides spp.). The study focused primarily on the relationship between characteristic ecosystems suitable for bluetongue vectors and climate, as well as on the phenology and population dynamics of these vectors. Twelve locations were selected, distributed over four distinct habitats: a wetland area, three riverine systems, four peat land areas and four livestock farms. Culicoides populations were sampled continuously using CO 2-baited counterflow traps from July 2005 until August 2006, with an interruption from November 2005 to March 2006. All vectors were identified to species level. Meteorological and environmental data were collected at each location. Culicoides species were found in all four different habitat types studied. Wetland areas and peat bogs were rich in Culicoides spp. The taxonomic groups Culicoides obsoletus (Meigen) and Culicoides pulicaris (Linnaeus) were strongly associated with farms. Eighty-eight percent of all Culicoides consisted of the taxon C. obsoletus/ Culicoides scoticus. On the livestock farms, 3% of Culicoides existed of the alleged bluetongue vector Culicoides dewulfi Goetghebuer. Culicoides impunctatus Goetghebuer was strongly associated with wetland and peat bog. Many Culicoides species were found until late in the phenological season and their activity was strongly associated with climate throughout the year. High annual variations in population dynamics were observed within the same study areas, which were probably caused by annual variations in environmental conditions. The study demonstrates that candidate vectors of bluetongue virus are present in natural and livestock-farm habitats in the Netherlands, distributed widely across the country. Under favourable climatic conditions, following virus introduction, bluetongue can spread among livestock (cattle, sheep and goats), depending on the nature of the viral serotype. The question now arises whether the virus can survive the winter conditions in north-western Europe and whether measures can be taken that effectively halt further spread of the disease.

Phylogenetic relationships of the subgenus Avaritia Fox, 1955 including Culicoides obsoletus (Diptera, Ceratopogonidae) in Italy based on internal transcribed spacer 2 ribosomal DNA sequences

Abstract. Biting midges of the genus Culicoides include vector species for orbiviral diseases, such as bluetongue and African horse sickness. Although the Afro‐Asiatic species C. imicola is the major vector of bluetongue in the Mediterranean basin, recent outbreaks in regions where C. imicola is absent has incriminated other Culicoides, including those belonging to the Obsoletus Complex of the subgenus Avaritia Fox, 1955. The classical taxonomy of this species complex is unclear and this stimulated the molecular analysis of twenty Culicoides populations sampled from eighteen localities across Italy. Ribosomal internal transcribed spacer 2 sequences were used to characterize the intra‐ and interspecific variation between Italian members of the Obsoletus Complex and related species, by means of an analysis of molecular variance and phylogenetic analyses. Although morphological differentiation is often extremely difficult, the molecular analysis clearly demonstrated a high degree of divergence between most species. The study showed that at least seven species of the subgenus Avaritia occur in Italy; these are C. obsoletus, C. scoticus, C. montanus, C. dewulfi, C. imicola and two species that could not be identified with certainty, but one of which is similar to C. chiopterus. Finally, a simple polymerase chain reaction assay was developed that rapidly discriminates between four members of the Obsoletus Complex in Italy, a prerequisite for vector identification.

Seasonal changes in Larval populations of Culicoides subimmaculatus Lee & Reye (Diptera: Ceratopogonidae), with observations on the influence of tides on larval ecology

At Tingalpa Creek, Brisbane, larvae and pupae of Culicoides subimmaculatus were most numerous 1.94 m above datum, midway between mean high-water neaps and mean high-water springs. Monitoring of a field population of immature stages indicated that C. subimmaculatus completes four generations a year, and overwinters in the 4th larval instar. Adults emerge during synchronized periods associated with the lunar tidal cycle; however laboratory experiments indicated that tidal coverage did not affect the time of adult eclosion or of pupation. It is suggested that synchronization occurs at an earlier point in the life cycle, possibly at ecdysis of 3rd to 4th instars.

Survival and Blood-Feeding Rate of Some Culicoides Species (Diptera: Ceratopogonidae) in Israel

Vector survival and blood-feeding rate are important components of vectorial capacity, and their measurement may help to identify disease foci. These parameters were estimated for populations of Culicoides spp. (Diptera: Ceratopogonidae) in Israel during the spring of 1981. Mean survival rate per gonotrophic cycle varied from 0.15 for C. newsteadi Austen at Newe Ya'ar, 0.20 to 0.27 for C. obsoletus Meigen at Kabri, to 0.26 to 0.47 for C. imicola Kieffer at Bet-Dagan. The gonotrophic cycle varied from 2 to 6 days. It was concluded that the potential vectorial capacity was very low at the sites and season of sampling.

EFFECT OF SEASON AND SAMPLING METHOD ON CULICOIDES (DIPTERA: CERATOPOGONIDAE) SPECIES CAUGHT AT TWO ESTUARINE SITES IN SOUTHEAST QUEENSLAND

ABSTRACT Culicoides populations were sampled at two tidal stream localities near Brisbane (Tingalpa Creek and Boggy Creek), using light traps, a truck trap and human bait. Twenty‐three species of Culicoides were collected during two and a half years of field work.Species composition was comparable at both sites, with C. subimmaculatus Lee and Reye being the most abundant species. At Tingalpa Creek C. subimmaculatus formed 63% of light trap catches, 4% of truck trap catches and 99.7% of human bait catches. C. brevitarsis Kieffer (35%) and C. marmoratus (Skuse) (32%) predominated in truck trap collections.Females of all species were more abundant than males in light trap samples and in all but three of the more common species caught by the truck trap. All specimens collected from human bait were female. Seasonal variation in relative abundance of species was observed in light and truck trap samples.

Comparative Host-Seeking Activity of Culicdides (Diptera: Ceratopogonidae) Attracted to Pastured Livestock in Central New York State, USA1

Populations of host-seeking Culicoides spp. attracted to calves, ponies and sheep were sampled to characterize and compare host attraction rates, landing patterns, seasonal activity periods and parity profiles. A customized vacuum aspirator was used to take samples from the belly, brisket, back and neck regions of animals positioned in paired combinations on open pasture. Sample dates were 18 evenings from June through September 1976. Culicoides biguttatus, C. obsoletus , and C. stellifer were captured in large numbers, and from each animal. Culicoides spinostus, C. venustus, C. sanguisuga and C. variipennis , in order of abundance, were captured less frequently; the capture of C. venustus from calves and sheep is the first record of attraction to a potential blood meal source. With the exception of C. spinosus , which was attracted to dorsal regions of animals, each species was attracted in greatest numbers to the belly region. Female C. biguttatus and C. stellifer were captured in significantly greater numbers from calves than sheep, and in similar numbers from calves and ponies. In contrast, C. obsoletus was captured in comparable numbers from calves and sheep, and in significantly greater numbers from calves than ponies. These observations show that pastured livestock in central New York State are exposed to previously unappreciated levels of Culicoides blood-feeding activity throughout the summer months.

Isolation of viruses from field populations of culicoides (Diptera: Ceratopogonidae) in Nigeria.

From November 1967 through December 1970, nearly 270,000 specimens of Culicoides were processed for viral assay at the Virus Research Laboratory, Ibadan, Nigeria. Seventy isolates of 16 different viruses were obtained. Thirteen of the viruses belong to recognized serogroups: Simbu group (Sabo, Sango, Sathuperi, Shamonda, Shuni), Palyam group (Abadina), rabies group (kotonkan), bluetongue group (bluetongue, 3 agents related to the virus of epizootic hemorrhagic disease of deer), Ganjam group (Dugbe), and Congo group (Congo). The other 3 are ungrouped: Rift Valley fever and 2 agents still under study. Some of these viruses were previously associated only with mosquitoes and ticks. In addition, several of them that cause economically important diseases had never before been detected in southern Nigeria. The techniques used and the value of sampling Culicoides populations for monitoring the presence of viral agents are discussed.

Species of Culicoides breeding on rocks and riverbanks in Nigeria

Abstract Catches of Culicoides made on a rocky hill and river bank in south‐western Nigeria showed Culicoides grahami and C.distinctipennis to be dominant. The former was most active at dusk and the latter at dawn. The number of matured eggs in the gravid female Culicoides caught on the hill and riverbank was low compared with those in gravid females of the same species caught around livestock. The fat bodies of all the dissected nulliparous and newly emerged Culicoides were full and large; those of the parous ones were depleted and inconspicuous except in individuals caught between June and July. The crop of most of the adult Culicoides contained colourless to dark yellowish fluid. C.grahami was the most numerous of the newly‐emerged species followed by C.distinctipennis. On the rocky hill, Culicoides bred in rotholes and boggy ground in between the rocks; at the river bank, breeding sites were underneath partially waterlogged canoes, in crabholes and other crevices, and underneath rotten vegetation. The influence of rainfall on the Culicoides population is discussed. Most of the species had adapted themselves to nectar feeding and autogeny was common. Perhaps some species aestivate during the hot dry season.

Comparison of Culicoides1 Larval Habitats and Populations in Central Iowa2

The predominant habitat types for larval Culicoides in central Iowa are flowing fresh-water. Nine species of Culicoides Latreille were collected from this and several other habitat types. Larval habitats of Culicoides were compared statistically by community ordination on the basis of species composition and relative density. In addition, habitat soil was analyzed for p H, sodium ion concentration, and organic matter content to examine relationships between these factors and the occurrence and abundance of Culicoides populations .

Intersexes in Culicoides spp. Caused by Mermithid Parasitism in Florida1

Certain mermithid nematodes have been found to parasitize 11 of the most abundant soil-dwelling (as larvae) species of Culicoides in Alachua County, Florida. The parasitism results in the production of intersexual forms in C. haematopotus Malloch, C. Stellifer (Coquillet). and C. crepuscularis Malloch, the genetically intended males being altered morphologically to resemble anterior-posterior type gynandromorphs while the females are not noticeably changed. The highest percentages of parasitism based upon males captured in emergence cages and light traps varied from 30 to 90% in localized areas. The nematodes are believed to effect a perceptible degree of natural control of Culicoides populations under favorable conditions.