The dying of the light: crepuscular activity in Culicoides and impact on light trap efficacy at temperate latitudes

The light trap is the tool of choice for conducting large-scale Culicoides (Diptera: Ceratopogonidae) vector surveillance programmes. Its efficacy is in doubt, however. To assess this, hourly changes in Culicoides activity over the 24-h diel were determined comparatively by way of light trapping and aerial sweeping, and correlated against light intensity. In the Netherlands, sweeping around cattle at pasture revealed that, in early summer, Culicoides are active throughout the diel, and that their abundance peaks during the crepuscular period and falls to a low during the brightest hours of the day. By contrast, the light trap was able to accumulate Culicoides only at night (i.e. after illuminance levels had dropped to 0 lux and midge activity had begun to decline). Although Culicoides chiopterus and species of the Culicoides obsoletus complex were similarly abundant around livestock, they differed critically in their hours of peak activity, being largely diurnal and nocturnal, respectively. This polarity helps to explain why, routinely, the C. obsoletus complex dominates light trap collections and C. chiopterus does not. Inability to accumulate Culicoides at light intensity levels above 0 lux means that, at ever-higher latitudes, particularly beyond 45° N, the progressive northward lengthening of the twilight period will have an increasingly adverse impact upon the efficacy of the light trap as a vector surveillance tool.

Culicoides (Diptera: Ceratopogonidae) and livestock in the Netherlands: comparing host preference and attack rates on a Shetland pony, a dairy cow, and a sheep

Culicoides (Diptera: Ceratopogonidae) host preferences and attack rates were quantified in early summer at a dairy farm in the Netherlands using livestock tethered at pasture. Midges were aspirated hourly over seven consecutive hours (17:00-23:00) from a dairy cow, a Shetland pony, and a sheep and correspondingly yielded seventeen, thirteen, and nine species. Of the 14,181 midges obtained, approximately 95% belonged to the C. obsoletus complex, C. dewulfi, C. chiopterus, and C. punctatus that together include all proven or potential vectors for arboviral diseases in livestock in northwestern Europe. On average, 7.6 and 3.5 times more Culicoides were collected, respectively, from the cow and the Shetland pony than from the sheep. In descending order of abundance, the C. obsoletus complex, C. dewulfi, and C. chiopterus dominated attacks on all three hosts, whereas C. punctatus and C. pulicaris favored only the two larger hosts. Irrespective of the host species involved, the three body regions attracted the same component species, C. chiopterus favoring the legs, C. punctatus and C. achrayi the belly, and the C. obsoletus complex, C. dewulfi, and C. pulicaris the head, back, and flanks. That known and potential vectors for animal diseases feed indiscriminately on a broad range of mammal hosts means that all major livestock species, including equines, are rendered susceptible to one or more Culicoides-borne pathogens.

An unrecognized species of the Culicoides obsoletus complex feeding on livestock in The Netherlands

In studies on Culicoides attacking livestock in the Netherlands, we chanced upon a species of the Obsoletus complex that we do not recognize, but whose dark wing pattern is distinctive. Nine cytochrome c oxidase (CO1) sequences of our so-called 'dark obsoletus' support its status as a separate species, the sequences differing significantly from those representing Culicoides obsoletus (Meigen) (90-91% homology) and Culicoides scoticus Downes & Kettle (87-88% homology). In the last decade, several research groups in Europe have encountered 'mystery species' related to C. obsoletus and in some instances have made their sequences for various genetic loci available in GenBank. These include a CO1 series submitted from Sweden in 2012 (annotated as 'obsoletus 01, 02, or 03 MA-2012') and of which some share a 99% identity with our sequences for 'dark obsoletus'. Without doubt, the series from the Netherlands, along with a portion of the Swedish submissions, together represent a single species ('dark obsoletus'). Whether this species is referable to the Russian Culicoides gornostaevae Mirzaeva recorded recently from Norway, Sweden and Poland, and based solely upon the external morphology of the male, is not clear. The presence in Western Europe of multiple undescribed species related to C. obsoletus means that the taxonomy of this important vector complex is not fully resolved; consequently, we know little about these cryptic species with regard to seasonality, geographic range and host preference. This is undesirable given that Culicoides-borne arboviruses causing disease in livestock are moving more regularly out of the tropics and spreading north into temperate latitudes.

Culicoides (Diptera: Ceratopogonidae) host preferences and biting rates in the Netherlands: comparing cattle, sheep and the black-light suction trap

Host preference is an important determinant of feeding behaviour in biting insects and a critical component in the transmission of vector-borne diseases. The aim of the study was to quantify Culicoides (Diptera: Ceratopogonidae) host preferences and biting rates using tethered livestock at pasture (a dairy cow and a sheep) and to compare the numbers of biting midges aspirated off them to those captured simultaneously in a black-light suction trap acting as a surrogate host. Culicoides collections were made hourly over seven hours (from five hours before official sunset to two hours after) between 27 May and 19 June, 2013 at a dairy farm (eastern Netherlands). The study involved 13 replicates of a site × host randomised design. Culicoides collected by black-light suction trap and by direct aspiration were identified to species morphologically and age-graded. The C. obsoletus complex, C. dewulfi and C. pulicaris predominated on the back and flanks of the animals, C. punctatus on the belly, and C. chiopterus on the legs. Using comparable collection periods, 9.3 times (95% confidence interval: 8.6-10.0) more Culicoides were caught on the cow than on the sheep and 25.4 times (95% confidence interval: 18.4-35.1) less in the black-light suction trap compared to the sheep. Mean Culicoides biting rates on the cow across the 7-h collection period were 4.6, 3.5, 1.0, 1.0 and 0.5 min(-1) for C. dewulfi, the C. obsoletus complex, C. chiopterus, C. punctatus and C. pulicaris, respectively; for the sheep they were 0.6, 0.4 and 0.1 min(-1) for the C. obsoletus complex, C. dewulfi and C. punctatus, respectively. Though midges were aspirated off livestock during each of the seven hours, they only began to appear in the black-light suction trap 5h later, from sunset onwards. After sunset, its efficacy improved markedly, but occurred when midge activity overall had begun to decline. Though it was quite accurate in ranking Culicoides species abundance, the black-light suction trap proved to be of limited value for determining hours of peak biting activity, levels of abundance, and host preference, in Culicoides.

Principal climatic and edaphic determinants of Culicoides biting midge abundance during the 2007-2008 bluetongue epidemic in the Netherlands, based on OVI light trap data

Palaearctic Culicoides midges (Diptera: Ceratopogonidae) represent a vital link in the northward advance of certain arboviral pathogens of livestock such as that caused by bluetongue virus. The effects of relevant ecological factors on weekly Culicoides vector abundances during the bluetongue virus serotype 8 epidemics in the Netherlands in 2007 and 2008 were quantified within a hurdle modelling framework. The relative role of meteorological parameters showed a broadly consistent association across species, with larger catches linked to temperature-related variables and lower wind speed. Moreover, vector abundance was found to be influenced by edaphic factors, likely related to species-specific breeding habitat preferences that differed markedly amongst some species. This is the first study on Culicoides vector species in the Netherlands identified during an entomological surveillance programme, in which an attempt is made to pinpoint the factors that influence midge abundance levels. In addition to providing key inputs into risk-mitigating tools for midge-borne pathogens and disease transmission models, the adoption of methods that explicitly address certain features of abundance datasets (frequent zero-count observations and over-dispersion) helped enhance the robustness of the ecological analysis.

The Mondrian matrix: Culicoides biting midge abundance and seasonal incidence during the 2006-2008 epidemic of bluetongue in the Netherlands

During the northern Europe epidemic of bluetongue (BT), Onderstepoort-type blacklight traps were used to capture Culicoides Latreille (Diptera: Ceratopogonidae) biting midges weekly between November 2006 and December 2008 on 21 livestock farms in the Netherlands. Proven and potential vectors for the bluetongue virus (BTV) comprised almost 80% of the midges collected: the Obsoletus complex, constituting C. obsoletus (Meigen) and C. scoticus Downes & Kettle (44.2%), C. dewulfi Goetghebuer (16.4%), C. chiopterus (Meigen) (16.3%) and C. pulicaris (Linnaeus) (0.1%). Half of the 24 commonest species of Culicoides captured completed only one (univoltine) or two (bivoltine) generations annually, whereas multivoltine species (including all BTV vectors) cycled through five to six generations (exceeding the one to four generations calculated in earlier decades). Whether this increment signals a change in the phenology of northern Europe Culicoides or simply is an adaptive response that manifests during warmer episodes, thus heightening periodically the incursive potential of midge-borne arboviruses, remains to be clarified. Culicoides duddingstoni Kettle & Lawson, C. grisescens Edwards, C. maritimus Kieffer, C. pallidicornis Kieffer and C. riethi Kieffer are new records for the biting midge fauna of the Netherlands. It is suggested that C. punctatus (Meigen) be added to the European list of vector Culicoides.

Schmallenberg Virus in Culicoides Biting Midges in the Netherlands in 2012

A total of 130 pools of Culicoides biting midges collected between May and September 2012 in the Netherlands were assayed for Schmallenberg virus (SBV). The Culicoides midges were caught in the same area as where in 2011 a high proportion of Culicoides pools tested positive for SBV, in majority with a high viral load (Ct values between 20 and 30). Two of a total of 42 pools comprising 50 midges/pool of the Obsoletus complex from the 2012 collection tested weak positive (Ct values: 34.96 and 37.66), indicating a relatively low viral load. On an individual midge level, the proportion of SBV-infected Culicoides of the Obsoletus complex caught in the same area and in a comparable period of the year was significantly lower in 2012 (0.1% = 1 per 1050 tested) compared with 2011 (0.56% = 13 per 2300 tested).

Mapping the basic reproduction number (R₀) for vector-borne diseases: a case study on bluetongue virus

Geographical maps indicating the value of the basic reproduction number, R₀, can be used to identify areas of higher risk for an outbreak after an introduction. We develop a methodology to create R₀ maps for vector-borne diseases, using bluetongue virus as a case study. This method provides a tool for gauging the extent of environmental effects on disease emergence. The method involves integrating vector-abundance data with statistical approaches to predict abundance from satellite imagery and with the biologically mechanistic modelling that underlies R₀. We illustrate the method with three applications for bluetongue virus in the Netherlands: 1) a simple R₀ map for the situation in September 2006, 2) species-specific R₀ maps based on satellite-data derived predictions, and 3) monthly R₀ maps throughout the year. These applications ought to be considered as a proof-of-principle and illustrations of the methods described, rather than as ready-to-use risk maps. Altogether, this is a first step towards an integrative method to predict risk of establishment of diseases based on mathematical modelling combined with a geographic information system that may comprise climatic variables, landscape features, land use, and other relevant factors determining the risk of establishment for bluetongue as well as of other emerging vector-borne diseases.

Endophily in Culicoides associated with BTV-infected cattle in the province of Limburg, south-eastern Netherlands, 2006

Culicoides were captured at a BTV-infected dairy near Gulpen in the province of Limburg (south-east Netherlands) between 14 September and 4 October 2006. Onderstepoort-type blacklight traps were used to sample Culicoides both inside and outside a partially open shed housing 11 cattle. A total of 28 light trap collections were made at the shed and yielded: 9371 Culicoides representing 11 species; >90% comprised five potential vectors of BTV and in order of abundance were Culicoides obsoletus and Culicoides scoticus (of the Obsoletus Complex), Culicoides dewulfi, Culicoides pulicaris and Culicoides chiopterus; Culicoides imicola, the principal Mediterranean (and African) vector of BTV, was absent. 2339 Culicoides representing seven species were captured inside (endophily) the cattle shed; >95% comprised the Obsoletus Complex and C. dewulfi. Conversely, the Pulicaris Complex, represented by five species and including C. pulicaris, showed strong exophily with >97% captured outside the shed. 7032 Culicoides were captured outside the shed, approximately threefold more than inside. This trend was reversed on an overcast day, when eightfold more Culicoides were captured inside; this indicates that when the light intensity outdoors is low Culicoides will attack (i) earlier in the day while cattle are still at pasture, and (ii) might follow cattle into the sheds in the late afternoon leading to elevated numbers of biting midges being trapped inside the shed during the subsequent hours of darkness. Culicoides were captured inside the shed on all 14 sampling nights. On occasion up to 33% were freshly blood fed indicating they had avidly attacked the cattle inside (endophagy); because half the cattle had seroconverted to BTV, and because no cattle were left outdoors at night, the data indicate that (i) the housing of animals in partially open buildings does not interrupt the transmission of BTV, and/or (ii) BTV is being transmitted while cattle are grazing outdoors during the day. The capture of partially engorged midges inside the shed shows they are being disturbed while feeding; this may lead to cattle being attacked repeatedly, and if these attacks include older parous BTV-infected Culicoides, may enhance virus dissemination (particularly in sheds where cattle stand close together). Endo- and exophagy by potential vector Culicoides--coupled to increased adult longevity and multiple feeding events in single (potentially) infected midges--would ensure an R0 of >1, resulting in the continued maintenance and spread of BTV within local vertebrate populations. Four light trap collections made additionally in a mature deciduous forest 70 m from the shed yielded a high proportion (48%) of gravid females amongst which 10% had incompletely digested blackened blood meals in their abdomens; the absence of this age category in Culicoides captured at the sheds indicates that all Culicoides, after engorgement, exit the buildings to undergo oogenesis elsewhere. In Europe, the blacklight trap is used widely for the nocturnal monitoring of Culicoides; a drawback to this approach is that this trap cannot be used to sample midges that are active during the day. Because diurnal biting in vector Culicoides may constitute a significant and underestimated component of BTV transmission a novel capture methodology will be required in future and is discussed briefly.

The Culicoides 'snapshot': a novel approach used to assess vector densities widely and rapidly during the 2006 outbreak of bluetongue (BT) in The Netherlands

A novel method was developed and implemented during the recent outbreak of bluetongue (BT) in sheep and cattle in The Netherlands to obtain rapidly a 'snapshot' of Culicoides vector densities at the national level. The country was divided into 110 raster cells, each measuring 20 km x 20 km; within 106 of these cells, a farm was selected with a minimum of 10 cattle and sampled for Culicoides for one night only using the Onderstepoort-type blacklight trap. Prior to deployment of the light traps in the field, local veterinarians were trained in their use and in the preservation of captured Culicoides. The collections were dispatched daily by courier to a field laboratory where the Culicoides were counted and identified. The 'snapshot' commenced on 12 September 2006 and was completed on 28 September coinciding with the 5-7 weeks of BT virus (BTV) activity in The Netherlands and when the number of weekly cases of disease was on the rise. Analysis of the 106 collections was completed on 5 October. The number of grid cells in which a taxon occurred is represented by the index 20(2) gFR (=20 km x 20 km grid Frequency Rate); this index essentially reflects the percentage of examined raster cells found to contain the potential vector in question. The 'snapshot' results can be summarised as follows: A total of >35,000 Culicoides were captured (mu=333 midges/light trap) representing 16 species; Not a single specimen of C. imicola, the principal Afro-Asiatic vector of BTV in southern Europe, was captured; The three European species of Culicoides implicated previously as potential vectors in the Mediterranean region and the Balkans also occur in The Netherlands; The Obsoletus Complex (represented by both potential vectors Culicoides obsoletus and Culicoides scoticus) was the most prevalent taxon (20(2) gFR: 93.4%) followed by the Pulicaris Complex (76.4%); The Pulicaris Complex comprised at least six species. One of these, Culicoides pulicaris sensu stricto (ss), a potential vector in southern Europe, had a low 20(2) gFR of 17.9% indicating it played no role in the transmission of BTV; The next most prevalent taxa were Culicoides dewulfi (70.8%) and Culicoides chiopterus (67.0%) both of which breed in cattle dung. This close association with livestock raises their potential as vectors of BTV; Culicoides achrayi, Culicoides circumscriptus, C. dewulfi, Culicoides halophilus, Culicoides lupicaris and Culicoides stigma are new species records for The Netherlands and demonstrates that the extant knowledge on the Culicoides fauna of northern Europe is incomplete; Cooling trends in the weather induced a >50-fold decrease in overall Culicoides numbers but with subsequent warming these would rebound rapidly indicating that more intense cold is required before heightened mortalities are induced amongst adult biting midges. The northward advance of BT in Europe compels the competent authorities in affected and in neighbouring territories to acquire rapidly baseline information around which to plan sound vector surveillance and livestock movement strategies. The Culicoides 'snapshot' is a tool well suited to this purpose. It is stressed that a vector surveillance program must be built upon a firm taxonomic base because misidentifications will flaw the mapped seasonal and geographic distribution patterns upon which veterinary authorities depend.

Influence of biotic and abiotic factors on the distribution and abundance of Culicoides imicola and the Obsoletus Complex in Italy

Culicoides imicola Kieffer (Culicoides, Diptera: Ceratopogonidae) is the principal vector of bluetongue virus (BTV) to ruminant livestock in southern Europe. The secondary potential vectors are Culicoides obsoletus (Meigen) and Culicoides scoticus Downes and Kettle of the Obsoletus Complex, Culicoides pulicaris (Linnaeus) of the Pulicaris Complex and Culicoides dewulfi Goetghebuer of the subgenus Avaritia Fox. Between 2000 and 2004 >38,000 light-trap collections were made for Culicoides across Italy including the islands of Sardinia and Sicily. Mapping of the 100 largest collections of C. imicola and of the Obsoletus Complex showed them to be disjunct overlapping in only 2% of the 200 municipalities selected. For each municipality the average values were calculated for minimum temperature, aridity index, altitude, terrain slope, normalised difference vegetation index (NDVI) and percentage forest cover. A factor analysis identified two principal factors ('biotic' and 'abiotic') and explained 84% of the total variability; a discriminant analysis classified correctly 87.5% of the observations. The results indicate adult populations of C. imicola to occur in more sparsely vegetated habitats that are exposed to full sunlight, whereas species of the Obsoletus Complex favour a more shaded habitat, with increased green leaf density. Heliophily and umbrophily, by shortening or lengthening the respective adult life cycles of these two vectors, will likely impact on the ability of each to transmit BTV and is discussed in the light of the current outbreak of BTV across the Mediterranean Basin.

Comparative descriptions of the pupae of five species of the Culicoides imicola complex (Diptera, Ceratopogonidae) from South Africa

The viruses causing the economically important livestock diseases of African horse sickness (AHS) and bluetongue (BT) are transmitted by biting midges of the genus Culicoides (Diptera, Ceratopogonidae). In the Old World the most important vectors of these diseases are Culicoides imicola Kieffer, 1913, Culicoides brevitarsis Kieffer, 1917 and Culicoides bolitinos Meiswinkel, 1989. All three of these vectors belong to the Imicola complex of the subgenus Avaritia Fox, 1955. This species complex now comprises 12 sibling species; ten occur in sub-Saharan Africa and are difficult to identify (based mostly on subtle variations in the wing latterns) and so additional methods of reliable identification are needed. The pupal exuviae of the five commonest sibling species (C. imicola, C. bolitinos, Culicoides loxodontis Meiswinkel, 1992, Culicoides tuttifrutti Meiswinkel, Cornet & Dyce, 2003 and Culicoides sp. # 107) harvested from a variety of large herbivore dung types and from decaying fruits, are described and illustrated in detail. It is shown that they can be differentiated clearly on a number of morphological characters and, furthermore, are separable into two distinct groups based (principally) on the shape of the respiratory organ. A key for identifying and differentiating these five pupae is provided. Also, the pupa of the Oriental-Australasian C. brevitarsis was compared with its allopatric sister taxon, C. bolitinos. Because they share a common larval habitat (cattle and buffalo dung) and are almost inseparable in the adult phenotype, the question of their possible synonymy is raised. However, their respective pupae could not be differentiated on gross morphology and so it is argued that this unresolved problem requires a molecular solution.

Phylogeny of the subgenus Culicoides and related species in Italy, inferred from internal transcribed spacer 2 ribosomal DNA sequences

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) include vectors for the economically important animal diseases, bluetongue (BT) and African horse sickness (AHS). In the Mediterranean Basin, these diseases are transmitted by four species of Culicoides: the first three belong in the subgenus Avaritia Fox and are Culicoides imicola Kieffer, Culicoides obsoletus (Meigen) and Culicoides scoticus Downes and Kettle; the fourth is Culicoides pulicaris (Linnaeus) in the subgenus Culicoides Latreille. In the Palaearctic Region, this subgenus (usually referred to as the C. pulicaris group) now includes a loose miscellany of some 50 taxa. The lack of clarity surrounding its taxonomy stimulated the present morphological and molecular study of 11 species collected in Italy. Phylogenetic analysis of nuclear ribosomal DNA internal transcribed spacer 2 (ITS2) sequence variation demonstrated a high degree of divergence. These results, combined with those from a parallel morphological study, disclosed: (1) that some previously described taxa should be resurrected from synonymy; (2) that there are new species to be described; (3) that the subgenus Culicoides (as currently employed) is a polyphyletic assemblage of four lineages - the subgenus Culicoides sensu stricto, the subgenus Silvicola Mirzaeva and Isaev, the subgenus Hoffmania Fox and the hitherto unrecognized Fagineus species complex. Each is discussed briefly (but not defined) and its constituent Palaearctic taxa listed. Strong congruence between morphological and molecular data holds promise for resolving many of the difficult taxonomic issues plaguing the accurate identification of vector Culicoides around the world.

Description and implementation of a surveillance network for bluetongue in the Balkans and in adjoining areas of south-eastern Europe

During the recent severe outbreaks of bluetongue (BT) in the Mediterranean Basin, the BT virus (BTV) spread beyond its historical limits into the Balkan region. One of the primary impacts of BT is the cessation in livestock trade which can have severe economic and social consequences. The authors briefly describe the development of the collaborative East-BTnet programme which aims to assist all affected and at-risk Balkan states and adjoining countries in the management of BT, and in the development of individual national surveillance systems. The beneficiary countries involved, and led by the World organisation for animal health (Office International des Epizooties) Collaborating Centre for veterinary training, epidemiology, food safety and animal welfare of the Istituto Zooprofilattico dell'Abruzzo e del Molise 'G. Caporale' in collaboration with the Institute for the Protection and the Security of the Citizen, the European Commission Joint Research Centre (IPSC-JRC), were Albania, Bosnia-Herzegovina, Bulgaria, Croatia, Cyprus, the Former Yugoslavia Republic of Macedonia, Kosovo, Malta, Romania, Serbia and Montenegro, Slovenia and Turkey. A regional web-based surveillance network is a valuable tool for controlling and managing transboundary animal diseases such as BT. Its implementation in the Balkan region and in adjoining areas of south-eastern Europe is described and discussed.

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.

The taxonomy of Culicoides vector complexes - unfinished business

The thirty species of Culicoides biting midges that play a greater or lesser role in the transmission of bluetongue (BT) disease in the pantropical regions of the world are listed. Where known, each species is assigned to its correct subgenus and species complex. In the Mediterranean region there are four species of Culicoides involved in the transmission of BT and belong in the subgenera Avaritia Fox, 1955 (three species) and Culicoides Latreille, 1809 (one species). Using both morphological and molecular second internal transcribed spacer (ITS2) sequence data, the authors reappraise the taxonomy of these four species and their congeners. A total of 56 populations of Culicoides collected from across Italy and representing 17 species (18 including the outgroup taxon C. imicola Kieffer, 1913) were analysed. The findings revealed the following: C. imicola is the only species of the Imicola Complex (subgenus Avaritia) to occur in the Mediterranean region. In Europe the subgenera Avaritia and Culicoides (usually, but not quite correctly, equated with the C. obsoletus and C. pulicaris groups, respectively) are both polyphyletic, each comprising three or more species complexes (including a hitherto unknown complex). About half the species studied could not be identified with certainty; furthermore, the results indicate that at least three previously described species of Palaearctic Culicoides should be resurrected from synonymy. Finally, a high level of taxonomic congruence occurred between the morphological and the molecular data. One of the 'new' vector species, C. pulicaris, was described by the father of taxonomy, Carl Linnaeus, in 1758, but today, almost 250 years later, no monograph has appeared that treats the Culicoides fauna of the northern hemisphere as a whole. At a time when such economically important livestock diseases as BT are affecting ever larger areas of Europe, it would seem appropriate to commence the production of such a monograph to aid in the field identification of vector Culicoides. This 'unfinished business' might best be achieved through a collaborative network embracing all ceratopogonid specialists currently active in both the Palaearctic and Nearctic faunal realms.

Entomological surveillance for bluetongue on Malta: first report of Culicoides imicola Kieffer

A survey for Culicoides Latreille, 1809, was made on Malta in 2002 to establish whether Culicoides imicola Kieffer, 1913, the principal vector of bluetongue virus (BTV) in the Mediterranean Basin, or any other suspected vector species, was present. The collections and analyses were performed in accordance with the protocols of the National Reference Centre for Exotic Diseases (CESME Centro Studi Malattie Esotiche) in Teramo, Italy. Eighty-four catches were made between May and October at six permanent sites, namely: Mellieha, Rabat, San Gwann, Zejtun (Malta), Gharb and Sannat (Gozo island). The traps were placed near cattle (four farms), cattle and sheep (one farm: Rabat) and sheep and goats (one farm: Mellieha). Culicoides midges were found in 91.66% (77/84) of the catches and the highest number of midges per catch was 1 726. Culicoides imicola was confirmed on Malta for the first time in October 2002 and was found at four sites (San Gwann, Sannat, Gharb and Mellieha) but at very low abundance levels (<0.1% of the total Culicoides collected). Culicoides paolae Boorman, 1996 was the most widespread and abundant species (more than 80% of total Culicoides). Midges of the Obsoletus Complex were rare, with less than 10 individuals captured. Other species of Culicoides identified in the collections were: C. submaritimus Dzhafarov, 1962, C. cataneii Clastrier, 1957, C. circumscriptus Kieffer, 1918, C. jumineri Callot and Kremer, 1969, C. kingi Austen, 1912, C. maritimus Kieffer, 1924 and C. newsteadi Austen, 1921.

Entomological surveillance of bluetongue in Italy: methods of capture, catch analysis and identification of Culicoides biting midges

To elucidate the epidemiology of vector-borne diseases that can affect livestock in the Mediterranean Basin and elsewhere, it is essential to obtain a clear understanding of the life-cycle and habits of the vector insects involved. One purpose of such investigations is to provide data for an epidemiological surveillance system. As this depends heavily upon the collection of specimens in the field, it is necessary to establish the kinds of information required, and how it can be obtained. This requires, in turn, that the method (and instrument) of capture be standardised, so that all data are as complete as possible, are comparable, and are informative at many levels. Within the surveillance system for bluetongue (BT) in Italy, the National Reference Centre for Exotic Diseases (CESME: Centro Studi Malattie Esotiche) is leading an intensive and countrywide survey for Culicoides (Diptera: Ceratopogonidae) using standardised methods and protocols developed in collaboration with the Onderstepoort Veterinary Institute in South Africa. These methods have now also been implemented outside Italy in Malta, Croatia, Albania and Romania. This system includes the field protocols developed for the collection of Culicoides, the laboratory protocols developed around the insect analyses and the computer-based recording of all field data. Finally, the authors provide an 'Easy key' for the rapid identification of the principal BT vector C. imicola, and for grouping species that belong to the Obsoletus and Pulicaris vector complexes, and to the Nubeculosus and Schultzei potential vector complexes.

Adult characters defining and separating the Imicola and Orientalis species complexes of the subgenus Avaritia Fox, 1955 (Culicoides, Diptera: Ceratopogonidae)

Thirty-six subgenera comprise the biting midge genus Culicoides Latreille, 1809. One of these, the relatively small subgenus Avaritia Fox, 1955, is the most important as it contains nearly half of the 30 world species of Culicoides known to play a greater or lesser role in the transmission of orbiviral diseases to livestock pantropically. These diseases include bluetongue (BT), African horse sickness (AHS) and epizootic haemorrhagic disease of deer (EHD). The subgenus Avaritia is distributed globally and the 70 species described have been subdivided into seven species groups and four subgroups. These 11 informal categories, variously labelled as either 'subgroups', 'groups' or 'complexes', are reduced here to seven in number (six species complexes and one subgroup) and although they appear natural, they are nearly all poorly defined. In this study two of these, namely the Imicola and Orientalis species complexes, are re-evaluated to determine which morphological characters define them more precisely, and so may help to establish their monophyly in the future. The two complexes are separable on eight discrete adult characters (two in the female, six in the male); these characters, and three secondary ones, are discussed and illustrated. The Imicola and Orientalis Complexes together embrace 23 species; these species are assigned to their respective complexes and according to recent nomenclatural adjustments. The taxonomy of vector Culicoides worldwide remains superficial; to improve the situation it is recommended that the 'traditional' morphological method be integrated with the 'modern' molecular approach.

The isolation of bluetongue virus from field populations of the Obsoletus Complex in central Italy

Between July and September 2002, bluetongue (BT) virus (BTV) serotypes 2 and 9 caused mortalities amongst sheep in the communities of San Gregorio Magno (Salerno, Campania), Laviano (Salerno, Campania) and Carpino (Foggia, Puglia), central Italy. On three of the affected farms, approximately 10,000 specimens of Culicoides were captured, representing fifteen species. Not a single specimen of the classical Afro-Asiatic BT vector, C. imicola Kieffer, was found; species of the Obsoletus Complex dominated the light-trap collections (90%) and included C. obsoletus (Meigen), C. scoticus Downes and Kettle and C. dewulfi Goetghebuer. Fifty-eight pools of the Obsoletus Complex (excluding C. dewulfi), each numbering 100 individuals per pool, and containing only parous and gravid females, were assayed for virus. BTV serotype 2 (BTV-2) was isolated from three pools (San Gregorio and Carpino) and BTV-9 from one (Laviano). These results indicate clearly that a species other than C. imicola is involved in the current re-emergence of BT in the Mediterranean Basin, but whether this is only C. obsoletus sensu stricto, or only C. scoticus, or both together, has yet to be established.

Multiple vectors and their differing ecologies: observations on two bluetongue and African horse sickness vector Culicoides species in South Africa

Blacklight traps were used to collect Culicoides biting midges weekly between September 1996 and August 1998 at 40 sites distributed equidistantly across South Africa. The seasonal and geographic prevalences of 86 species of Culicoides were elucidated simultaneously, and included C. imicola Kieffer and C. bolitinos Meiswinkel the principal vectors of bluetongue (BT) and African horse sickness (AHS) in the region. These two species were amongst the most prevalent Culicoides to be found and, together, comprised >50% of the more than three million biting midges captured. The data are presented as coloured matrices, and are transformed also into inverse distance weighting (IDW) interpolative maps. The data reveal that the prevalence of each vector is somewhat fractured and it is posited that this is (in part) due to significant differences in their respective breeding habitats. The results illustrate also that the presence of multiple vectors (in any region of the world) will complicate both the epidemiology of the orbiviral diseases they transmit and the formulation of rational livestock movement and disease control strategies. This is especially true for southern Europe where the recent devastating cycle of BT has been shown to involve at least three vectors. Finally, the influence that man has on the development of large foci of vector Culicoides around livestock may be less important than previously suggested but must be investigated further.

Distribution and abundance of Culicoides imicola, Obsoletus Complex and Pulicaris Complex (Diptera: Ceratopogonidae) in Italy

Between 2000 and 2003, thousands of light-trap collections for Culicoides were made throughout Italy and a detailed distribution map of the primary vector of bluetongue (BT) virus (BTV), C. imicola compiled. In some areas, however, where clinical BT occurred and C. imicola could not be captured, the virus was isolated from biting midges belonging to the Obsoletus and/or the Pulicaris Complexes. Thus, the distribution and abundance of these two species complexes in Italy, as determined from about 3,000 collections, are reported here also and compared to that of C. imicola (from about 24,000 collections). The probable spread of the main vector of BT, C. imicola, into the northern third of Italy, and the widespread prevalence of additional vectors of the Obsoletus and Pulicaris Complexes, indicate nearly all regions of Italy to be at some risk to incursions of BTV. However, these complexes comprise at least six and twelve species, respectively, so precisely which species are able to transmit BTV remains incompletely known.

Towards the identification of potential infectious sites for bluetongue in Italy: a spatial analysis approach based on the distribution of Culicoides imicola

A geographic information system (GIS) based on grids was developed by the National Reference Center for Veterinary Epidemiology at the Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale' (IZS) in Teramo to identify potential infectious sites for bluetongue (BT) disease in Italy. Geographical and climatic variables were used to build a spatial process model (SPM); the different layers were combined by sequential addition. The final grids (with a cell size of 0.0387 decimal degrees) were generated for each season of the year, and the suitability of each cell for the presence of C. imicola given a value ranking from 0 to 10. While this model more accurately predicts the presence of C. imicola in the Basilicata and Sicily regions, it still over-predicted its presence in the Puglia region. This could be due to the occurrence of calcareous soils which dominate the Puglia landscape. The present SPM is an additive model that assigns an equal weight to each variable. However, the results suggest the existence of hitherto unconsidered variables that significantly influence the prevalence of C. imicola. To reflect their importance, these variables should be assigned a higher weighting in future models. However, the decision in regard to precisely what this weighting should be depends on a very thorough knowledge of the ecology of C. imicola.

Christopher Columbus and Culicoides: was C. jamaicensis Edwards, 1922 introduced into the Mediterranean 500 years ago and later re-named C. paolae Boorman 1996?

The biting midge, Culicoides paolae Boorman, described from specimens collected in the extreme south of Italy in 1996, belongs in the subgenus Drymodesmyia. This subgenus was erected by Vargas in 1960 for the so-called Copiosus species group, an assemblage of 22 species endemic to the tropical regions of the New World and, where known, breed in vegetative materials including the decaying leaves (cladodes) and fruits of Central American cacti. The Mexican peoples have utilised these cacti for over 9,000 years; one of these, Opuntia ficus-indica Linnaeus, was brought to Europe by Christopher Columbus following his voyages of discovery. As a taxon C. paolae is very similar to the Central American C. jamaicensis Edwards, 1922 raising the possibility that it (or a closely related species of Drymodesmyia) was introduced into the Mediterranean Region at the time of Columbus, but was (perplexingly) discovered only 500 years later and named C. paolae. The comparison of Sardinian specimens of C. paolae with Panamanian material of C. jamaicensis (housed in the Natural History Museum in London) confirmed the two species to be very similar but unusual differences were noted around the precise distribution of the sensilla coeloconica on the female flagellum. Until it is understood whether these differences represent either intra- or interspecific variation, the question of the possible synonymy of C. paolae must be held in abeyance.

Phylogenetic status and matrilineal structure of the biting midge, Culicoides imicola, in Portugal, Rhodes and Israel

The biting midge Culicoides imicola Kieffer (Diptera: Ceratopogonidae) is the most important Old World vector of African horse sickness (AHS) and bluetongue (BT). Recent increases of BT incidence in the Mediterranean basin are attributed to its increased abundance and distribution. The phylogenetic status and genetic structure of C. imicola in this region are unknown, despite the importance of these aspects for BT epidemiology in the North American BT vector. In this study, analyses of partial mitochondrial cytochrome oxidase subunit I gene (COI) sequences were used to infer phylogenetic relationships among 50 C. imicola from Portugal, Rhodes, Israel, and South Africa and four other species of the Imicola Complex from southern Africa, and to estimate levels of matrilineal subdivision in C. imicola between Portugal and Israel. Eleven haplotypes were detected in C. imicola, and these formed one well-supported clade in maximum likelihood and Bayesian trees implying that the C. imicola samples comprise one phylogenetic species. Molecular variance was distributed mainly between Portugal and Israel, with no haplotypes shared between these countries, suggesting that female-mediated gene flow at this scale has been either limited or non-existent. Our results provide phylogenetic evidence that C. imicola in the study areas are potentially competent AHS and BT vectors. The geographical structure of the C. imicola COI haplotypes was concordant with that of BT virus serotypes in recent BT outbreaks in the Mediterranean basin, suggesting that population subdivision in its vector can impose spatial constraints on BT virus transmission.

Evidence for a new field Culicoides vector of African horse sickness in South Africa

Between February and May 1998, approximately 100 horses died of African horse sickness (AHS) in the cooler, mountainous, central region of South Africa. On 14 affected farms, 156,875 Culicoides of 27 species were captured. C. imicola Kieffer, hitherto considered the only field vector for AHS virus (AHSV), constituted <1% of the total Culicoides captured, and was not found on 29% of the farms. In contrast, 65% of the Culicoides were C. bolitinos Meiswinkel, and was found on all farms. Five isolations of AHSV were made from C. bolitinos, and none from 18 other species of Culicoides (including C. imicola).

The distribution of Culicoides imicola in Italy: application and evaluation of current Mediterranean models based on climate

In August 2000 bluetongue (BT) disease appeared amongst sheep on the island of Sardinia spreading later to Sicily and to mainland Italy. The majority of areas affected by BT were surveyed for Culicoides imicola, the only proven vector of the disease known to occur in the Mediterranean region. The data from 1456 light-trap collections, made in months with a mean temperature of 12.5 degrees C, were used to test the accuracy of current models predicting the prevalence and abundance of C. imicola across the region. For Italy, the distribution of C. imicola was found to be very irregular and did not fit the modelled predictions. The possible reasons for this are discussed, and suggestions made as to which variables may improve this fit in the development of future risk models. In Italy, past surveys failed to reveal the presence of C. imicola, and so could be construed as evidence of its recent invasion, and thus rampant spread northwards. Although equivocal, historical records indicate that C. imicola was overlooked in the past. Six recommendations are made as to the possible future course of Culicoides research in southern Europe.

The effect of climate on the presence of Culicoides imicola in Italy

A model was developed to classify the Italian territories in relation to their suitability to harbour populations of Culicoides imicola and, as a consequence, also able to sustain a bluetongue (BT) epidemic. Italy was subdivided into 3507 10 x 10 km cells. In 546 cells at least one collection was made. The cell was considered the unit for all subsequent analyses. Culicoides were collected using Onderstepoort-type blacklight traps. Some traps were operated weekly at chosen sites; the remainder were moved almost daily to new sites. Only the results obtained during the peak August-November period were used, to exclude bias caused by the seasonality of C. imicola. Climate data for the period 1999-2001 were obtained from 80 weather stations. Multiple logistic regression was performed using the presence or absence of C. imicola in a specific cell as the dependent variable. Annual means of daily values for minimum temperature and minimum relative humidity, and the mean altitude above sea level, were the independent variables. The probability of occurrence of C. imicola in each grid cell was used to create a prediction map for Italy. The model was able to correctly classify 77.5% of the 546 grid cells in which at least one collection had been made. Culicoides imicola was found frequently through much of Sardinia, in parts of southern Italy, and further north along the Tyrrhenian coast, but was absent from along most of the Adriatic coast, and the internal mainland, and from most of Sicily. Six detailed maps are provided. Also mapped are areas where the probability of the occurrence of C. imicola is lower than 5%. This identification of possible mountainous C. imicola-free areas in central Italy could facilitate safer animal trade and transhumance, even if BT infections in traded animals or moving stock, were to go undetected. Needless to say this depends upon no cool-adapted species of Culicoides being involved in the transmission of BT disease.

Phylogenetic analysis of the mitochondrial cytochrome oxidase subunit I gene of five species of the Culicoides imicola species complex

The phylogenetic status of members of the Culicoides imicola Kieffer (Diptera: Ceratopogonidae) species complex of haematophagous midges is unknown, and simple means to identify the members using all life stages are unavailable. In this study, the status of three confirmed (C. imicola s.s., C. bolitinos Meiswinkel and C. loxodontis Meiswinkel) and two provisional (C. tuttifrutti Meiswinkel and C. kwagga Meiswinkel) members of the complex from South Africa was assessed using phylogenetic analysis of partial DNA and amino acid sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene. The four or five individuals of each species analysed contained one or two haplotypes each. Interspecific divergence was significant and characterized by strong A <--> T transversion bias. Phylogenetic trees constructed using neighbour-joining, parsimony and maximum likelihood showed each species to be distinct. Combinations of sites for two restriction enzymes in the COI sequences were species-specific and could form the basis of a diagnostic PCR assay.

Prevalence of Culicoides imicola and other species (Diptera: Ceratopogonidae) ateight sites in Zimbabwe : to the editor

Presents some prevalence data on Culicoides imicola and Culicoides bolitinos in Zimbabwe. Includes data on other common species, as revealed by collections made over 2 years at 8 widely-separated study sites

Molecular differentiation of the Old World Culicoides imicola species complex (Diptera, Ceratopogonidae), inferred using random amplified polymorphic DNA markers

Samples of seven of the 10 morphological species of midges of the Culicoides imicola complex were considered. The importance of this species complex is connected to its vectorial capacity for African horse sickness virus (AHSV) and bluetongue virus (BTV). Consequently, the risk of transmission may vary dramatically, depending upon the particular cryptic species present in a given area. The species complex is confined to the Old World and our samples were collected in Southern Africa, Madagascar and the Ivory Coast. Genomic DNA of 350 randomly sampled individual midges from 19 populations was amplified using four 20-mer primers by the random amplified polymorphic DNA (RAPD) technique. One hundred and ninety-six interpretable polymorphic bands were obtained. Species-specific RAPD profiles were defined and for five species diagnostic RAPD fragments were identified. A high degree of polymorphism was detected in the species complex, most of which was observed within populations (from 64 to 76%). Principal coordinate analysis (PCO) and cluster analysis provided an estimate of the degree of variation between and within populations and species. There was substantial concordance between the taxonomies derived from morphological and molecular data. The amount and the different distributions of genetic (RAPD) variation among the taxa can be associated to their life histories, i.e. the abundance and distribution of the larval breeding sites and their seasonality.

Stabling and the protection of horses from Culicoides bolitinos (Diptera: Ceratopogonidae), a recently identified vector of African horse sickness

The stabling of horses at night reportedly offers protection from African horse sickness and the most significant vector of the disease, Culicoides imicola Kieffer, has been shown to be exophilic. In certain high-lying regions of South Africa, however, C. bolitinos Meiswinkel, may be the major vector of the disease but its entry behaviour into stables is unknown. Accordingly, in the eastern Free State province of South Africa, light trap catches of C. bolitinos inside stables and outside, were compared. Two horse-baited stables, one traditional, and one modern, were used and combinations of stable (old/new), ceiling fans (on/off) and accessibility to Culicoides (stable doors open/closed or windows gauzed/ungauzed) were investigated as treatments. A total of 111,452 Culicoides of 26 species was collected on 60 trap nights; C. bolitinos was dominant (89.1% overall) with C. imicola second in abundance (2.9%). Outside catches were greater on warmer, drier, evenings but were suppressed by high wind speeds. Catches of C. imicola inside stables with doors open, or with windows ungauzed, were less than the numbers captured outside. In contrast, more C. bolitinos were caught in open stables than outside, i.e. open structures may protect horses from the exophilic C. imicola, but may increase attack rates from the endophilic C. bolitinos. The closing of doors and the gauzing of windows, however, led to a 14-fold reduction in numbers of C. bolitinos and C. imicola entering stables. A well-gauzed 'traditional' stable was as effective as a closed 'modern' stable. Ceiling fans had no suppressant effect.

A preliminary attempt to use climate data and satellite imagery to model the abundance and distribution of Culicoides imicola (Diptera: Ceratopogonidae) in southern Africa

Abundances of Culicoides imicola, the insect vector of several livestock viruses, including bluetongue and African horse sickness, were recently published for 34 sites in southern Africa, together with associated climate data. Here, these data are analysed statistically in combination with certain satellite-derived variables, with the aim of developing predictive models of C. imicola abundance. Satellite-derived variables were the land surface temperature (LST, a measure of temperature at the earth's surface) and the normalised difference vegetation index (NDVI, a measure of photosynthetic activity). Two models were developed: (1) climatic variables only and (2) satellite-derived and climatic variables. For model I, the best model used a single predictor variable (the mean daily minimum temperature) only, and accounted for nearly 34% of the variance in C. imicola abundance. Two variable climatic models did not perform significantly better. For model II, the best 1-variable model used the annual minimum LST as a predictor of C. imicola abundance, and accounted for nearly 40% of the variance in C. imicola abundance. The best 2-variable model, which gave a significantly better fit than the 1-variable model, combined the minimum LST and minimum NDVI as predictors of C. imicola abundance, and accounted for nearly 67% of variance. A map of predicted C. imicola abundances is produced on the basis of this 2nd model which, despite some anomalies, agrees largely with what is currently known of the prevalence of C. imicola in the region.

The 1996 outbreak of African horse sickness in South Africa--the entomological perspective

During the 1996 summer season (January-April) in South Africa an estimated 500 horses died of African horse sickness (AHS); 80% of deaths were due to AHS virus serotypes 2 and 4. Nearly all cases occurred in the northern, north-eastern and central parts of South Africa. This study reports the first attempt to verify the involvement of the biting midge Culicoides imicola in a field outbreak of AHS in southern Africa. In light-trap collections made at 47 sites over 12 weeks, C. imicola comprised 94.2% of 4.78 million Culicoides. Culicoides imicola was the most prevalent of 34 species captured and was the only species whose distribution matched that of the disease. Record catches of C. imicola were made, and reveal that in years of above average rainfall its numbers can show a 200-fold increase over those in dry years. Soil type appeared to determine strongly the distribution of C. imicola. The largest populations of C. imicola were found in areas with clayey, moisture-retentive soils whereas the lowest numbers, or none, occurred in areas where the soils were sandy and quick-draining. The deaths of two horses (confirmed AHS) in a sandy area were perplexing as they occurred in a region known to be free of C. imicola. The probable origin of these infections was established.

Some epidemiological and economic aspects of a bluetongue-like disease in cattle in South Africa--1995/96 and 1997

In December 1995 to March 1996 and the early summer of 1997 South Africa experienced above average rainfall which favoured the occurrence of Culicoides transmitted diseases. During this period several outbreaks of an uncommon disease of cattle occurred over a large part of the country. The clinical signs were similar to those of infection with the viruses of bluetongue (BT) and epizootic haemorrhagic disease of deer (EHD). Virus isolation from cattle and Culicoides yielded both viruses. Dual infections occurred on several farms. Typing of BT isolates yielded types 2, 3, 6 and 8. On at least two farms more than one BT virus serotype was involved. On one farm only EHD virus could be isolated from cattle and Culicoides. Serological tests confirmed that on this farm the disease was caused by EHD. In 1932/33, when a similar disease was reported conditions were vastly different. Rainfall figures show that the 1932/33 season was exceptionally dry. Techniques available at that time could not identify EHD and the cause was reported to be BT. The occurrence of BT in a dry season and over a much wider area than the distribution in South Africa of Culicoides imicola, the only proven vector for BT, is a clear indication that other species less dependent on high rainfall are involved. The present isolation of BT virus from three of five pools of parous C. bolitinos is evidence that this species, which breeds in cattle dung, may be an additional vector for BT.

Morphological confirmation of the separate species status of Culicoides (Avaritia) nudipalpis Delfinado, 1961 and C. (A.) imicola Kieffer, 1913 (Diptera: Ceratopogonidae)

Ten character states were used to compare five females and two males of two populations of C. nudipalpis from the Philippines and Timor in south-east Asia with 121 females and 167 males of 11 populations of C. imicola collected throughout its Afro-Asiatic range. It is concluded that they are closely related but good species, and together form a subgroup, or species-pair, in the imicola group; currently this Old World group of the subgenus Avaritia comprises seven described species. Culicoides nudipalpis and C. imicola are most reliably separated on the ratio of the length of the proboscis to the height of the head (P/H ratio: 0.66-0.73 in nudipalpis, 0.82-1.02 in imicola). Compared to C. imicola very little is known of the life habits of C. nudipalpis. The latter's close taxonomic relationship to C. imicola, a proven vector of African horse sickness (AHS) and bluetongue (BT), indicates that the capacity of C. nudipalpis to vector these orbiviruses deserves to be investigated.

Discovery of a Culicoides imicola-free zone in South Africa: preliminary notes and potential significance

In December 1993, a light-trap survey was made of the Culicoides found at eight horse stables and dairies in the sandy dune field west of Port Elizabeth, South Africa. While it was notable that Culicoides numbers were low (4749) and that the diversity was poor (15 species), the most remarkable fact to emerge, was that C. imicola, the only proven vector of the virus of African horse sickness (AHS), was entirely absent. Though not abundant, C. bolitinos, a sister species of C. imicola, was overwhelmingly dominant (91.7%). Its larvae and pupae develop exclusively in the dung of cattle, but it is a species that is not implicated in the transmission of animal viruses. Elsewhere in South Africa, a frost-free climate, good rainfall and a plentiful supply of livestock would normally lead to the development of large foci of C. imicola. That this is not the case in the Port Elizabeth (P.E.) area is most likely owing to the winds inhibiting adult flight and the sandy soils being nutrient-poor and too well-drained to sustain Culicoides larvae. Studies are needed to confirm that sandy soils cannot sustain C. imicola. If so, the sandy coastal areas hold promise for quarantining against AHS.

Culicoides (Diptera:Ceratopogonidae) associated with livestock in the Onderstepoort area, Gauteng, South Africa as determined by light-trap collections

In 54 light-trap collections made at 28 sites in the Onderstepoort area a total of 178,941 Culicoides midges of 35 species was collected in March 1988; the survey was repeated at 26 sites in September and yielded 19,518 Culicoides of 24 species. The number of Culicoides species collected totalled 38. C,imicola was the most abundant species at 27 of the 28 sites sampled, and accounted for 88% and 67% of all midges collected in the two months respectively. This study not only confirms that C. imicola is widespread and abundant in the greater Onderstepoort area, but also that its numbers correlate positively with the historical prevalence of African horse sickness (AHS) and bluetongue (BT) locally. The high numbers of C. imicola make Onderstepoort the ideal site for the study of its laboratory vector capacity. The relatively low numbers of Culicoides spp. other than C. imicola in the Onderstepoort area, will severely limit studies on their roles in the transmission of arboviruses. The origin of the blood-meals of 1338 engorged Culicoides belonging to 13 species was determined by means of cross-over electrophoresis precipitin test; C. imicola fed on cattle, horses, sheep of pigs, Four other Culicoides species showed a similarly wide host range.

Tokunagahelea, a new subgenus of Culicoides Latreille (Diptera: Ceratopogonidae) from the Australasian region with descriptions of two new species

Tokunagahelea is proposed as a new subgenus of the genus Culicoides Latreille to embrace three species from New Guinea and the Solomon Islands. Comparative descriptions of both males and females of Culicoides mikros, sp. nov., and C. geocheloneoides, sp. nov., and a redescription of the female of C. pygmaeus Tokunaga (male unknown), are presented together with a key for differentiation. C. mikros is the designated type species of the subgenus. Systematic relationships of the new subgenus are discussed.

The virtual absence of Culicoides imicola (Diptera: Ceratopogonidae) in a light-trap survey of the colder, high-lying area of the eastern Orange Free State, South Africa, and implications for the transmission of arboviruses

Altogether 52 078 Culicoides biting midges of 35 species were collected during February 1990 and 1993 in 40 light-trap collections made on 17 cattle and/or sheep farms in the Bethlehem and Fouriesburg districts of the colder, high-lying eastern Orange Free State. Culicoides (Avaritia) bolitinos was by far the most abundant species, representing 50.9% of all specimens collected. Culicoides (A.) imicola, considered to be the most common stock-associated species in the summer rainfall areas of southern Africa, and the only proven vector of bluetongue virus (BTV) and African horsesickness virus (AHSV) in the subregion, was uncommon, comprising only 1.4%. While AHS is apparently absent, BT and bovine ephemeral fever (BEF) are endemic in this cooler, high-lying area of South Africa. The virtual absence of C. imicola implies that other Culicoides species, such as C. bolitinos and C. cornutus, may be involved in transmitting BT virus (and perhaps BEF) in the eastern Orange Free State, and possibly elsewhere in Africa. Virus isolation attempts made on 45 single species pools of C. bolitinos, C. pycnostictus, C. milnei, C. leucostictus, C. zuluensis and C. gulbenkiani were, however, negative. Finally, 20 of 28 blood-engorged Culicoides of 11 species, which were tested against cattle, sheep, horse, pig and bird antisera, tested only positive against cattle antisera.

African horsesickness epidemiology: five species of Culicoides (Diptera: Ceratopogonidae) collected live behind the ears and at the dung of the African elephant in the Kruger National Park, South Africa

During the culling of elephants (Loxodonta africana) at five sites in the Kruger National Park, South Africa, a total of 682 Culicoides of five species of the subgenus Avaritia were found live either behind the ears of elephants or attracted to the freshly disembowelled intestinal dung of elephants. The species are Culicoides tororoensis Khamala & Kettle, 1971; C. kanagai Khamala & Kettle, 1971; C. loxodontis Meiswinkel, 1992, and two undescribed species, i.e. Culicoides sp. #50 and Culicoides sp. #54 pale form (p.f.). Of 511 female midges found behind ears, 39.9% were nulliparous, 57.3% empty parous, 2.5% freshly bloodfed and 0.2% gravid. The age composition of this subpopulation indicates that the Culicoides were behind the ears to suck blood and, furthermore, would do so in broad daylight. The age composition of 171 Culicoides of three species attracted to dung was entirely different: 1.8% nulliparous, 14.6% empty parous, and 83.0% gravid, indicating that the great majority of midges captured at dung were about to oviposit or had just oviposited. Immediately after culling, light-traps were operated at two of the sites. Of 4,023 Culicoides of 21 species captured, 93% were of the same five species found on the ears and at the dung of elephants. Using these and other unpublished data pertaining to the rearing of these five Avaritia species from elephant dung over the past seven years, we broadly sketch the life cycle of these Culicoides, the first for any Afrotropical species of the genus. We also discuss the implications the close association between elephant and midge has for the dispersal and geographic distribution of the latter, and how it may influence the involvement of midges in the transmission of diseases such as African horsesickness. Owing to difficulties in identifying species of the subgenus Avaritia in the Afrotropical Region, the taxonomy of each of the five above-mentioned species is briefly appraised. Of the remaining 16 species (7%) captured in light traps 15 (6%) belong to that sector of the genus Culicoides whose immature stages develop in groundwater habitats and include C. imicola, which comprised only 2% of the light-trap collections. The large disparity in the adult abundance patterns of the "dung" and "groundwater" species in the middle of dry bushveld, is probably the result of differences in host and larval habitat preferences, and is briefly discussed. Finally, the few reports extant on the wild-host preferences of Afrotropical Culicoides are reviewed. Five tables and five figures accompany the text.

Subsampling of large light trap catches of Culicoides (Diptera: Ceratopogonidae)

Analyses of 2 light trap catches comprising 6,041 and 1,598 Culicoides showed that the reliability of subsampling such catches increased with subsample size, while the subsampling error decreased with an increase in the number of individuals per species present in a subsample. Subsamples comprising approximately 500 Culicoides are deemed sufficient for comparing population densities between sites and sampling occasions and also give an acceptable indication of relative species abundance at a site. It is recommended that species for which the mean number of specimens in subsamples originating from 3 catches at a site is less than 7, should not be included in biometric analyses aimed at comparisons of population densities. For all other species a test level of 1% rather than 5% should be used for such comparisons. When species ratios obtained from subsampled catches are employed as indicators of abundance, the chi-squared test should be utilized at a 1% level if the ratios originate from 3 catches at a site and at a 0.1% level if only one catch per site is made. Due to poor representativeness of small catches, it is suggested that species for which fewer than 7 individuals are present in a single subsample, be excluded from chi-squared tests. A 5-point procedure for subsampling a large light trap collection of Culicoides is given.