Models for the dispersal in Australia of the arbovirus vector, Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae)

Culicoides brevitarsis is the main biting midge responsible for the transmission of bluetongue and Akabane viruses to livestock in Australia. Models are given for its dispersal after winter from endemic areas at the southern limit of its distribution in New South Wales (NSW); the models might also be applicable elsewhere. Model 1 shows that dispersal can be explained by distance from a key point just outside the endemic area in mid-northern/northern coastal NSW. The model provides probability data for times of first occurrence at sites within regions down the southern coastal plain or up the Hunter Valley towards (but rarely reaching) the western slopes and tablelands. Model 2 shows that the movement depends on temperature and wind speed from northerly and easterly directions. Preliminary data also are given to suggest a relationship between density in the endemic area and the maximum distance that C. brevitarsis can travel in a given year. The models can be linked to other information which in combination can provide probabilities for winter survival outside the endemic area, times of occurrence at sites where it cannot survive winter and times when activity ceases naturally at these sites at the end of the season. This information can be used to predict the potential for virus transmission and indicate zones of seasonal freedom from both vector and virus for the export of livestock.     

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.     

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.     

Ecological correlates of bluetongue virus in Spain: predicted spatial occurrence and its relationship with the observed abundance of the potential Culicoides spp. vector

Using data from bluetongue (BT) outbreaks caused by viral serotype 4 (BTV-4) in Spain during 2004–2005, a predictive model for BTV-4 occurrence in peninsular Spain was developed. An autologistic regression model was employed to estimate the relationships between BTV-4 presence and bioclimatic-related and host-availability-related variables. In addition, the observed abundances of the main potential Culicoides vectors during 2004–2005, namely Culicoides imicola, Culicoides obsoletus group, and species of the Culicoides pulicaris group, were compared between BTV-4 presence/absence areas predicted by the model.BTV-4 occurrence was mainly explained by bioclimatic variables, although a consideration of host-availability variables led to improved fit of the model. The area of BTV-4 presence predicted by the model largely resembled the core distribution area of C. imicola, and this species was the most abundant Culicoides spp. in predicted BTV-4 presence areas. The results suggest that the spatial expansion of BTV-4 took place only as far as those areas in which C. imicola populations efficiently transmitted the virus.     

Bluetongue and Douglas virus activity in New South Wales in 1989: further evidence for long-distance dispersal of the biting midge Culicoides brevitarsis

SUMMARY: Infection of cattle with bluetongue and Douglas viruses was detected on the central and southern coast of New South Wales from January to April 1989. Bluetongue virus infection was found well south of areas of expected occurrence. Evidence is presented to support wind-borne dispersal of infected vectors, Culicoides brevitarsis , southwards from the Hunter Valley.     

The survival of nematodes and cestodes of sheep in the pasture during the winter in eastern Norway

Using 21 worm-free lambs in paddocks on old sheep pastures on 4 farms near Oslo, it was found that Nematodirus spp., Ostertagia spp. and Moniezia spp. were the only helminths which could survive the winter in the pasture in great numbers. A few Teladorsagia davtiani, Chabertia ovina, Trichuris ovis, Cooperia onchophora and Skrjabinema ovis survived the winter. Trichostrongylus axei, T. vitrinus and Oesophagostomum venulosnm showed a negligible ability to survive the winter in the pasture. The following species were never found to survive: Haemonchus contortus, Trichostrongylus colubriformis, Bunostomum trigonocephalum, Cooperia curticei and Strongyloides papillosus.     

Prediction of areas around the Mediterranean at risk of bluetongue by modelling the distribution of its vector using satellite imaging.

Bluetongue is an infectious disease of ruminants caused by a virus transmitted by biting midges, one species of which, Culicoides imicola, is the major vector in the Old World. Following an epizootic of African horse sickness,a related disease, in Iberia and Morocco between 1987 and 1991, C imicola was trapped for two years at 44 sites in the affected region and models were developed for predicting the abundance of C imicola at these sites. Discriminant analysis was applied to identify the best model of three levels of abundance from 40 Fourier-processed remotely sensed variables and a digital elevation model. The best model correctly predicted the abundance level at 41 of the 44 sites. The single most important variable was the phase of the annual cycle of the normalised difference vegetation index. The model was used to predict the abundances of C imicola elsewhere around the Mediterranean and predicted high levels of abundance in many areas recently affected by bluetongue, including the Balearics, Sardinia, Sicily, eastern Greece, western Turkey, Tunisia and northern Algeria. The model suggests that eastern Spain, the island of Ibiza, the provinces of Lazio and Puglia in Italy, the Peloponnese and parts of northern Algeria and Libya may be at risk of bluetongue in 2001.     

Genetic variation of bluetongue virus serotype 11 isolated from host (sheep) and vector (Culicoides variipennis) at the same site

Genetic relatedness of 2 strains of bluetongue virus (BTV) serotype 11 that were isolated from the same geographic site--one from host (sheep) and the other from the vector Culicoides variipennis during an enzootic of bluetongue at Bruneau, Idaho, in August 1973--was determined by comparing the oligonucleotide fingerprint analyses of the individual double-stranded RNA segments of the genomes. It was observed that the 2 strains of BTV-11 exhibit considerable differences in their genotypes, the percentage of diversity being different for each of the corresponding RNA species of the 2 strains of BTV-11. These results indicate that more than one genotype of BTV can circulate in juxtaposition in a given geographic site. The observed genotypic diversity might be due to the accumulation of point mutations on specific RNA species or antecedent reassortment of RNA segments between different BTV in nature or both.     

Patterns of morphometric variation in the alpine newt (Mesotriton alpestris) at the southern limit of its distribution: environmental correlates

We applied multivariate analyses to an array of body measures of alpine newt specimens derived from 11 local populations in Greece to describe, analyse and detect patterns and putative causes of within‐population and among‐population morphometric variation. The observed morphometric variation was partitioned into several independently varying aspects of the external phenotype, frequently following variation patterns in different environmental factors. The size and features of the aquatic habitat were found to affect body size, while altitude was found to affect head‐shape variation in both sexes. At the intra‐population level, variation in generalized body size and shape was found to be significantly lower when competitive newt species were present in the habitat, indicating stabilizing selection towards a decrease in inter‐specific competition. No clear discrimination on body size and shape proportions was detected between the two genetic lineages examined, implying ecogenetic or environmentally induced variation rather than phylogeny.     

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.     

Molecular detection of Culicoides spp. and Culicoides imicola, the principal vector of bluetongue (BT) and African horse sickness (AHS) in Africa and Europe

Bluetongue (BT) and African Horse Sickness (AHS) are infectious arthropod-borne viral diseases affecting ruminants and horses, respectively. Culicoides imicola Kieffer, 1913, a biting midge, is the principal vector of these livestock diseases in Africa and Europe. Recently bluetongue disease has re-emerged in the Mediterranean Basin and has had a devastating effect on the sheep industry in Italy and on the islands of Sicily, Sardinia, Corsica and the Balearics, but fortunately, has not penetrated onto mainland France and Spain. To survey for the presence of C. imicola, an extensive light-trap network for the collection of Culicoides, was implemented in 2002 in southern mainland France. The morphological identification of Culicoides can be both tedious and time-consuming because its size ranges from 1.5 to 3 mm. Therefore, an ITS1 rDNA polymerase chain reaction (PCR)-based diagnostic assay was developed to rapidly and reliably identify Culicoides spp. and C. imicola. The aim of this work was to set up a rapid test for the detection of C. imicola amongst a pool of insects collected in areas at risk for BT. The sequence similarity of the rDNA (nuclear ribosomal DNA), which is greater within species than between species, is the foundation of its utilisation in species-diagnostic assays. The alignment of the 11 ITS1 sequences of Culicoides obtained from Genbank and EMBL databases helped us to identify one region in the 5' end and one in the 3' end that appear highly conserved. PCR primers were designed within these regions to amplify genus-specific fragments. In order to set up a C. imicola-specific PCR, another forward primer was designed and used in combination with the previously designed reverse primer. These primers proved to be highly specific and sensitive and permitted a rapid diagnostic separation of C. imicola from Culicoides spp.     

秦岭羚牛冬季野外及人工生存情景浅析

秦岭羚牛生活在秦岭高海拔地区,属我国特有的一种珍稀野生牛科大型动物,是我国4种羚牛亚种之一,由于距离人们生活的环境较远,人们对其了解甚少.本文通过对秦岭羚牛野外特性的剖析,介绍人工饲养秦岭羚牛的设施和日粮组成,人工饲养注意事项,以期对羚牛这一野生动物的冬季野外天气保护提供借鉴.     

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 20kmx20km; 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 despatched 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 (=20kmx20km 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: 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.     

Culicoides trapping with Rothamsted suction traps before and during the bluetongue epidemic of 2006 in Belgium

The collection of biting midges was taking place some months before the first bluetongue outbreak in Belgium in August 2006. The Walloon Agricultural Research Centre had been monitoring aphid populations at two sites annually in Belgium (Gembloux and Libramont), using two stationary '12-m' Rothamsted suction traps. For the Gembloux trap, collections of insects captured daily from 11 May 2006 onwards were already available at the time of the outbreak. An examination of these samples revealed the presence of Culicoides, some species of which are considered as potential vectors of the bluetongue virus (BTV). The trapping was therefore extended beyond the normal aphid activity period and the Culicoides captured were identified to species level. From 11 May to 31 December 2006, the Gembloux trap caught 664 Culicoides specimens belonging to 19 species comprising known BTV-vectors. The second trap, at Libramont, was reactivated from 12 September to 13 October and caught 97 specimens belonging to nine species, all of which had been found at the Gembloux site. Among the 19 species identified, four were new to Belgian fauna: Culicoides achrayi, C. deltus, C. lupicaris and C. newsteadi. This paper examines the overall phenology and the physiological status of Culicoides in 2006 before and during the bluetongue epidemic. It discusses the potential of the Rothamsted suction trap to monitor Culicoides.     

浅谈桑螟虫的发生与防治

桑螟Diaphania pyloalis walker俗称青虫、卷叶虫、油虫,属鳞翅目螟蛾科,以幼虫期形态食危害桑叶,属桑树主要害虫之一。近年来翠屏区发生桑螟危害比较普遍,严重影响着蚕桑生产,给蚕农带来较大的损失。笔者通过近两年来对我区主要蚕区的桑螟危害进行了深入了解和调查后认为：若能及时全面掌握病虫信息