Effects of altitude, distance and waves of movement on the dispersal in Australia of the arbovirus vector, Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae)

The dispersal of the biting midge and arbovirus vector Culicoides brevitarsis in the Bellinger, Macleay and Hastings river valleys and up the escarpment of the great dividing range (GDR) of mid-northern coastal New South Wales, Australia, from 1995 to 2003 was studied. The midge moved up these valleys from the endemic coastal plain in at least two waves between October and May, and both waves were modelled. Dispersal time can be explained by direct distance from the coast and the altitude of the sites. Dispersal times due to distance were similar at 18.2 ± 2.2 (S.D.) and 15.9 ± 2.6 weeks per 100 km for first- and second-occurrences at fixed altitude. Time of the first wave was extended 0.48 ± 0.22 weeks for every 100-m rise in altitude and the second by 1.14 ± 0.24 weeks for every 100-m rise for a set distance. Although C. brevitarsis can move up the escarpment of the GDR (and possibly transmit virus), vector dispersal, survival and establishment at and beyond the top of the range are limited. A third model showed that previously described slower movement of C. brevitarsis up the more-southerly Hunter valley relative to movements down the coastal plain also was related to increasing altitude.     

Association between risk of seroconversion of sentinel cattle to bluetongue viruses and Culicoides species (Diptera: Ceratopogonidae) in Queensland, Australia

The association between risk of seroconversion of sentinel cattle to bluetongue viruses and the number of Culicoides brevitarsis Kieffer and C. wadai Kitaoka caught by light traps was investigated using survival analysis. Eight sentinel herds that seroconverted to bluetongue viruses between 1990 and 1994, and for which insect-trapping data were available, were selected for inclusion in the study. These herds were located at six sites along the eastern coast of Queensland, Australia, from approximately latitude 10 °South to 25 °South. C. brevitarsis was detected at all locations where sentinel herds were maintained, whereas C. wadai was detected at only two locations in northern Queensland where four sentinel herds were maintained during the study period. The mean number of C. brevitarsis and C. wadai caught per month was 230 and 21, respectively. A significant (P = 0.05) positive association was found between the risk of seroconversion of sentinel cattle to bluetongue viruses and the number of C. wadai caught in the same month.     

Culicoides (Diptera: Ceratopogonidae) associated with horses at Mogoditshane,Gaborone, Botswana

Veterinary Research Communications -     

Culicoides spp. (Diptera: Ceratopogonidae) Associated with Farmed Ostriches (Struthio camelus) in Botswana

Veterinary Research Communications -     

Newly emerged nulliparous Culicoides imicola Kieffer (Diptera: Ceratopogonidae) with pigmented abdomen

The method of segregating nulliparous and parous females of Culicoides spp. based on the presence of burgundy-red pigment inside the abdominal wall of parous Culicoides midges, is used worldwide. Out of 320 females of Culicoides imicola trapped by emergence traps, set over an artificial breeding site for 10 and 24 days, 73 (22.8%) showed a red-pigmentation despite the fact that they were nulliparous. This finding indicated that 23% of the “parous” females that are examined for the presence of arboviruses and other pathogens or for age-grading purposes, are actually old nulliparous females, which had no chance of acquiring pathogens. This bias in parous rate distorts upward the calculation of vectorial capacity.     

Seasonal dynamics of biting midges (Diptera: Ceratopogonidae: Culicoides), the potential vectors of bluetongue virus, in Sweden

The outbreak of bluetongue (BT) in northern Europe 2006 initiated the monitoring of vectors, biting midges of the genus Culicoides in Sweden. In order to determine the diversity, distribution and seasonal dynamics of Culicoides, weekly collections were made during 2008 and during March-December 2009 using the Ondestepoort Veterinary Institute black light trap. Twenty sampling sites were selected in 12 provinces. In total of 30,704 Culicoides were collected in 2008 and 32,252 in 2009. The most abundant species were the potential vectors of BTV Culicoides obsoletus/C. scoticus that comprised of 77% of the total catches. Other biting midges collected were Culicoides impunctatus (9%), Culicoides grisescens (3%), Culicoides punctatus (2%), Culicoides chiopterus (2%) and Culicoides pulicaris (2%). Culicoides obsoletus/C. scoticus were most abundant during May-June and August-September. The majority of the species were active from March to November in 2008 and April to October in 2009. Species considered as potential vectors of bluetongue virus (BTV) occurred as far north as latitude 65°N (Kalix).     

Evaluation of Culicoides insignis (Diptera: Ceratopogonidae) as a vector of bluetongue virus.

Based upon epidemiological evidence, Culicoides insignis Lutz is a probable biological vector of bluetongue viruses (BTV) in South Florida, the Caribbean Region and Central America. The vector potential of this species for BTV was evaluated in the laboratory in a series of experiments using insects caught in the field. Although there was great variation in the percentage of flies that fed from any one catch, it was demonstrated that C. insignis became infected after membrane feeding on a mixture of blood and virus. The infection rates ranged from 20 to 62.5%. Following intrathoracic inoculation, BTV replicated to high titres in C. insignis. Such flies were also shown to be capable of transmitting BTV to susceptible sheep and embryonated chicken eggs. This series of experiments provides the first conclusive evidence that C. insignis is a biological vector of bluetongue virus. This is the first proven vector of BTV in the neotropics.     

Immunogenicity and allergenicity of Culicoides imicola (Diptera: Ceratopogonidae) extracts

Summer seasonal recurrent dermatitis (SSRD) or "sweet itch" is a seasonally occurring allergic dermatitis of horses provoked by biting midges. The allergic skin reactions have been attributed to allergens present in various Culicoides species. C. imicola is the suspected etiological agent of SSRD in Israel. Whole body extracts of this midge induced hypersensitivity reactions upon injection into susceptible horses and in this study attempts were made to define components of C. imicola which have immunogenic and allergenic properties. Immunogenic potency was evaluated by raising antisera to whole body extracts of C. imicola in rabbits and examining their reactivity towards fractionated extracts. Allergenic potency was examined by reacting fractionated extracts with horse sera. Humoral reactivity of susceptible and non susceptible horses was assayed by specific IgE and IgG ELISAs. Although there are many antigenic components in whole body extracts of C.imicola capable of eliciting an immune response, no conclusive evidence was obtained indicating that allergic reactivity was associated with increased IgE levels of defined specificity.     

The dispersal of Culicoides brevitarsis in eastern New South Wales and associations with the occurrences of arbovirus infections in cattle

Distributions of the vector Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) (determined from light trap data) and 2 arboviruses (determined from seroconversions in sentinel cattle) were studied in eastern New South Wales in 1993–94. C brevitarsis was recorded progressively from endemic areas on the north coast, to Nowra on the south coast, and westward to Scone, in the Hunter Valley. C brevitarsis also survived through winter at Paterson, in the Hunter Valley. Its apparently focal reappearance in this marginal area had no obvious effect on the broad pattern of its progression or the dispersal of Akabane and bluetongue viruses. These viruses were first recorded from foci near Coffs Harbour, on the mid-north coast. Their first occurrences at different locations were associated with those of C brevitarsis, but not with each other. The viruses were found only within the recorded limits of the vector's distribution. Delays between the initial occurrence of C brevitarsis and first evidence of virus transmissions at locations ranged from 2 to 7 months. The delays decreased away from the points of focus and were negatively associated with the time of initial occurrence of the vector. Seroconversions to the viruses were related to the presence of C brevitarsis. However, the densities of C brevitarsis had no apparent effect on the initial numbers of cattle seroconverting to either virus. The results support the conclusion that the progressions of C brevitarsis and Akabane and bluetongue viruses were the result of gradual movements by the vector.     

Afrotropical Culicoides: C (Avaritia) miombo sp. nov., a widespread species closely allied to C. (A.) imicola Kieffer, 1913 (Diptera: Ceratopogonidae)

Culicoides (Avaritia) miombo sp. nov. is described and illustrated from both sexes collected in northern Malawi. Two references in the literature have previously referred to this new species as either C. brosseti Vattier & Adam or C. imicola Kieffer. A further 4 references are discussed that most likely deal with C. miombo sp. nov. and not C. brosseti. C. miombo sp. nov. is apparently widespread in subtropical and tropical Africa and is now recorded from Zimbabwe, Botswana, South Africa, Nigeria and the Ivory Coast. There are also probable records from Angola, Burkina Faso, Zambia and eastern Madagascar. On the African mainland, both north and south of the equator, the pattern of distribution of C. miombo sp. nov. correlates strongly with that of drier Guineo-Congolian rainforest, and Sudanian and Zambezian woodlands, the latter known as miombo in southern Africa. These phytochoria and associated biota are sensitive to frost and experience relatively high temperatures and rainfall-3 factors that appear to limit the distribution of C. miombo sp. nov. to north of the 20-22 degrees C mean annual temperature isotherms in southern Africa. The new species is a member of the Imicola group which consists of 6 species confined to the Afrotropical (including Madagascar), Oriental and eastern Palaearctic regions. One species has in historic times spread to Australia. The worldwide distribution of each species is briefly discussed. It is suggested that the Imicola and Orientalis groups are separate lineages within the subgenus Avaritia. Culicoides miombo sp. nov. is compared with its closest African congeners C. imicola, C. pseudopallidipennis Clastrier and C. bolitinos Meiswinkel; 15 character states are used to separate C. miombo sp. nov. and C. imicola. The female antennal and palpal measurements of C. miombo sp. nov. are subjected to statistical analysis to highlight their taxonomic usefulness. The larval habitat of C. miombo sp. nov. is unknown.     

Rearing of Culicoides nubeculosus (Diptera: Ceratopogonidae) by natural or artificial feeding in the laboratory

A technique for the mass rearing of Culicoides nubeculosus in the laboratory is described. Female midges were fed either on fresh or deep-frozen, defibrinated cattle blood (-70 degrees C) through latex membranes, or on anesthetized white mice. Feeding rates of up to 90% were obtained on the latex membrane, whereas only 41% of the midges fed on mice. The best oviposition rates of greater than 50% were achieved after feeding either on the latex membrane with fresh cattle blood or on mice. An average of greater than 100 eggs per female were deposited. The highest larval hatching rate was observed after feeding with fresh blood; about half of the larvae developed to the adult stage. A reproduction index was defined for the colony based on the feeding rate, oviposition rate, larval hatching rate and development to the adult stage. The highest reproduction index was obtained when the midges were fed on fresh cattle blood through the membrane.     

Bluetongue virus isolations from midges belonging to the Obsoletus complex (Culicoides, Diptera: Ceratopogonidae) in Italy

Between July and September 2002 there were outbreaks of bluetongue on three sheep holdings in the communities of San Gregorio Magno (Salerno, Campania), Laviano (Salerno, Campania) and Carpino (Foggia, Puglia), and the involvement of bluetongue virus (btv) was confirmed serologically and virologically. The mortality rate was at least 11 per cent and involved btv serotype 2 (btv-2) and serotype 9 (btv-9). These holdings were also surveyed for the Culicoides (Diptera: Ceratopogonidae) vectors; approximately 10,000 midges belonging to 15 species were captured, but they did not include a single specimen of the classical Afro-Asiatic bluetongue vector, Culicoides imicola. Species belonging to the Obsoletus complex dominated the light-trap collections, and Culicoides obsoletus Meigen, Culicoides scoticus Downes and Kettle and Culicoides dewulfi Goetghebuer constituted 90 per cent of all the Culicoides species captured. Fifty-six pools of the Obsoletus complex (excluding C dewulfi), each containing 100 individual midges and containing only parous and gravid females, were assayed for virus. btv-2 was isolated from three pools from San Gregorio Magno and Carpino, and btv-9 was isolated from one pool from Laviano. These results indicate that a species other than C imicola is involved in the current re-emergence of bluetongue in the Mediterranean Basin, but whether it is C obsoletus sensu stricto or C scoticus, or both, is uncertain.     

Chemical composition of silage residues sustaining the larval development of the Culicoides obsoletus/Culicoides scoticus species (Diptera: Ceratopogonidae)

Culicoides (Diptera: Ceratopogonidae) are biological vectors of bluetongue virus (BTV). Bluetongue is a viral disease that affects domestic and wild ruminants. Since its recent emergence in northern Europe, this disease has caused considerable economic losses to the sheep and cattle industry. The biotopes, and more particularly the chemical characteristics which are suitable for larval development of the main vector species, are still relatively unknown. This study shows that the larvae of biting midges belonging to the species Culicoides obsoletus and Culicoides scoticus are able to breed in different types of silage residue (maize, grass, sugar beet pulp and their combinations). The chemical composition of substrates strongly influences the presence of the immature stages of these biting midges. Higher lignin and insoluble fibre contents seem to favour their presence and could play the role of a physical support for semi-aquatic larvae. In contrast, higher concentrations of magnesium and calcium are negatively correlated with the presence of these two species. These data will help to locate and monitor the breeding sites of these species and could contribute to the control of these insects on farms.     

Seasonal allergic dermatitis in sheep in southern Brazil caused by Culicoides insignis (Diptera: Ceratopogonidae)

The incidence of seasonal dermatitis was studied in a Hampshire Down flock on a farm in southern Brazil. Epidemiological data, clinical signs and macroscopic pathology were obtained by visiting the farm. Histological lesions were studied in skin biopsies of affected sheep. Biting insects were collected from January to April 2005 in an attempt to identify the etiological agent of the disease. Disease prevalence was 40%; the age of the affected animals was variable. Disease occurred from December to March, some animals had lesions for the entire year. Clinical signs include pruritus on the ears, around the eyes and ventral abdomen. Initially erythema and small red papules were seen, followed by alopecia and crust formation. Histologically the lesions were characterized by perivascular eosinophilic dermatitis. Hyperkeratosis and acanthosis were observed in the chronic lesions. Both Anopheles albitarsis and Culicoides insignis were captured during the study. C. insignis bites caused pruritus in sheep. Both types of insects were caught when they approached the sheep baits approximately 30min after sunset. Results suggested that the disease occurred as a result of an immediate hypersensitivity reaction to C. insignis.     

Akabane epizootics in New South Wales: evidence for long-distance dispersal of the biting midge Culicoides brevitarsis

In 1983 an outbreak of Akabane disease occurred in calves in New South Wales between Coolah and Dunedoo at the foothills of the Liverpool Range, from Molong to Oberon in the Blue Mountains and in the Bylong Valley. These areas, at the time of infection of the dams, were in a drought and conditions were unsuitable for the multiplication of C. brevitarsis. In late March meteorological phenomena developed producing air movements favourable for transporting infected midges from the Hunter Valley. A re-examination of the data from the epizootics of 1974 and 1955 showed that similar weather systems had developed. It is possible that the source of infected midges in these epizootics was also the Hunter Valley.     

Abundance of biting midge species (Diptera: Ceratopogonidae,Culicoides spp.) on cattle farms in Korea

Culicoides biting midges were collected on three cattle farms weekly using light traps overnight from May to October between 2010 and 2011 in the southern part of Korea. The seasonal and geographical abundance of Culicodes spp. were measured. A total of 16,538 biting midges were collected from 2010 to 2011, including seven species of Culicoides, four of which represented 98.42% of the collected specimens. These four species were Culicodes (C.) punctatus (n = 14,413), C. arakawae (n = 1,120), C. oxystoma (n = 427), and C. maculatus (n = 318). C. punctatus was the predominant species (87.15%).     

Seasonal abundance and parity of Culicoides biting midges associated with livestock at Roma, Lesotho (Diptera: Ceratopogonidae)

A light-trap survey was undertaken of the species composition, seasonal abundance and parity of Culicoides at Roma, Lesotho, to establish whether the likely vectors for bluetongue and African horse sickness occur in this area as well as the chance of transmission. A total of 34 catches was made between 21 September 1985 and 24 September 1986; 32,819 Culicoides were caught belonging to 19 species. Culicoides numbers rapidly built up from December to a peak in February which implies that this may also be the optimum time for virus transmission. The number of Culicoides dropped sharply in April with the onset of cooler conditions. C. zuluensis was the dominant species forming 69.6% of the totalled catches, followed by C. pycnostictus with 11.7%. C. imicola, the only proven vector of bluetongue, was never abundant representing only 4.4% of the midges caught. The parous rate for each of the 2 commonest species was low, implying a low vector capacity.