Spatial distribution of bluetongue virus and its Culicoides vectors in Sicily

During the recent Mediterranean epizootic of bluetongue, an extensive programme of serological and vector (Culicoides biting midges (Diptera: Ceratopogonidae)) surveillance was carried out across Sicily. This paper presents the analysis of 911 light trap catches collected at the times of peak Culicoides abundance (summer to autumn 2000-2002) in 269 sites, in order to produce detailed maps of the spatial distribution of the main European vector, Culicoides imicola Kieffer and that of potential novel vectors. Whereas C. imicola was found at only 12% of sites, potential novel vectors, Culicoides obsoletus group Meigen, Culicoides pulicaris Linnaeus and Culicoides newsteadi Austen were present at over 50% of sites. However, the spatial distribution of C. imicola showed the closest correspondence to that of the 2000 and 2001 bluetongue (BT) outbreaks and its presence and abundance were significant predictors of the probability of an outbreak, suggesting that it was the main vector during these years. Although C. imicola may have played a role in transmission in several sites near Paternó, it was absent from the majority of sites at which outbreaks occurred in 2002 and from all sites in the province of Messina. All three potential novel vectors were widespread across sites at which outbreaks occurred during 2002. Of these, C. newsteadi was an unlikely candidate, as it was significantly less prevalent in outbreak vs. non-outbreak sites in Messina. It is hypothesized that the yearly distribution and intensity of outbreaks is directly attributable to the distribution and abundance of the vectors involved in transmission during each year. When C. imicola operated as the main vector in 2000 and 2001, outbreaks were few in number and were restricted to coastal regions due to low abundance and prevalence of this species. In 2002, it is hypothesized that BTV transmission was handed over to more prevalent and abundant novel vector species, leading to numerous and widespread outbreaks and probably to overwintering of the virus between 2001 and 2002. Based on catch ranges in outbreak vs. non-outbreak sites, it is tentatively suggested that nightly catches of 400 or more C. obsoletus and 150 or more C. pulicaris allow BTV transmission at a site, and provide a strategy for a fuller examination of the relationship between BTV transmission and the abundance and distribution of different vector species.     

Modelling the distributions of Culicoides bluetongue virus vectors in Sicily in relation to satellite-derived climate variables

Surveillance data from 268 sites in Sicily are used to develop climatic models for prediction of the distribution of the main European bluetongue virus (BTV) vector Culicoides imicola Kieffer (Diptera: Ceratopogonidae) and of potential novel vectors, Culicoides pulicaris Linnaeus, Culicoides obsoletus group Meigen and Culicoides newsteadi Austen. The models containing the 'best' climatic predictors of distribution for each species, were selected from combinations of 40 temporally Fourier-processed remotely sensed variables and altitude at a 1 km spatial resolution using discriminant analysis. Kappa values of around 0.6 for all species models indicated substantial levels of agreement between model predictions and observed data. Whilst the distributions of C. obsoletus group and C. newsteadi were predicted by temperature variables, those of C. pulicaris and C. imicola were determined mainly by normalized difference vegetation index (NDVI), a variable correlated with soil moisture and vegetation biomass and productivity. These models were used to predict species presence in unsampled pixels across Italy and for C. imicola across Europe and North Africa. The predicted continuous presence of C. pulicaris along the appenine mountains, from north to south Italy, suggests BTV transmission may be possible in a large proportion of this region and that seasonal transhumance (seasonal movement of livestock between upland and lowland pastures) even in C. imicola-free areas should not generally be considered safe. The predicted distribution of C. imicola distribution shows substantial agreement with observed surveillance data from Greece and Iberia (including the Balearics) and parts of mainland Italy (Lazio, Tuscany and areas of the Ionian coast) but is generally much more restricted than the observed distribution (in Sardinia, Corsica and Morocco). The low number of presence sites for C. imicola in Sicily meant that only a restricted range of potential C. imicola habitats were included in the training set and that predictions could only be made within this range. Future modelling exercises will use abundance data collected according to a standardized protocol across the Mediterranean and, for Sicily in particular, should include non-climatic environmental variables that may influence breeding site suitability such as soil type.     

Spatial and temporal distribution of bluetongue and its Culicoides vectors in Bulgaria

Surveillance of Culicoides (Diptera: Ceratopogonidae) biting midges was carried out between 2001 and 2003, at 119 sites within a 50 x 50-km grid distributed across Bulgaria, using light trap collections around the time of peak adult midge abundance. Sentinel and ad hoc serum surveillance of hosts susceptible to bluetongue infection was carried out at around 300 sites between 1999 and 2003. Following the initial incursion of bluetongue virus 9 (BTV-9) into Bourgas province in 1999, affecting 85 villages along the southern border, a further 76 villages were affected along the western border in 2001, with outbreaks extending as far north as 43.6 degrees N. The BTV-9 strain in circulation was found to have a low pathogenicity for Bulgarian sheep populations, with less than 2% of susceptible individuals becoming sick and seroconversions detected up to 30 km from recorded outbreaks in the south. The major Old World vector Culicoides imicola Kieffer was not detected among over 70,000 Culicoides identified in summer collections, suggesting that BTV-9 transmission in Bulgaria was primarily carried out by indigenous European vectors. The most likely candidates, the Palaearctic species complexes - the Culicoides obsoletus Meigen and C. pulicaris L. complexes - were widespread and abundant across the whole country. The C. obsoletus complex represented 75% of all individuals trapped in summer and occurred in high catch sizes (up to 15,000 individuals per night) but was not found across all outbreak sites, indicating that both Palearctic complexes probably played a role in transmission. Within the C. pulicaris complex, only C. pulicaris s.s., C. punctatus Meigen and C. newsteadi Austen were sufficiently abundant and prevalent to have been widely involved in transmission, whilst within the C. obsoletus complex most trapped males were C. obsoletus s.s. Adult vectors were found to be largely absent from sites in west Bulgaria for a period of at least 3 months over winter, which, taken along with the spatiotemporal pattern of outbreaks in the region between years, indicates the virus may be overwintering here by an alternative mechanism - either by covert persistence in the vertebrate host or possibly by persistence in larval stages of the vector.     

Spatial distribution of Culicoides species in Portugal in relation to the transmission of African horse sickness and bluetongue viruses

Surveillance of Culicoides (Diptera: Ceratopogonidae) biting midge vectors was carried out at 87 sites within a 50 x 50 km grid distributed across Portugal, using light trap collections at the time of peak midge abundance. Culicoides imicola (Kieffer) made up 66% of the 55 937 Culicoides in these summer collections. It was highly abundant in the central eastern portion of Portugal, between 37 degrees 5' N and 41 degrees 5' N, and in a band across to the Lisbon peninsula (at around 38 degrees 5' N). Of all the complexes, its distribution was most consistent with that of previous outbreaks of Culicoides-borne disease, suggesting that it may remain the major vector in Portugal. Its distribution was also broadly consistent with that predicted by a recent climate-driven model validating the use of remote sensing datasets for modelling of Culicoides distribution. Adult C. imicola were found to have overwintered at 12 of 20 sites re-surveyed in winter but it did so in very low numbers. Culicoides obsoletus (Meigen) and Culicoides pulicaris (Linnaeus) complex midges were widespread despite their low summer abundance. The observed coincidence of high abundances of C. imicola and high abundances of C. pulicaris in summer lead us to suggest that C. imicola could bring African horse sickness virus or bluetongue virus into contact with C. pulicaris and the latter complex, together with C. obsoletus, could then transmit these viruses across much wider areas of Europe. The fact that adult C. pulicaris are present in high abundances in winter may provide a mechanism by which these viruses can overwinter in these areas.     

Oral susceptibility of South African stock-associated Culicoides species to bluetongue virus

Field-collected South African Culicoides species (Diptera, Ceratopogonidae) were fed on sheep blood containing bluetongue virus (BTV) represented by 13 low-passage reference serotypes: -1, -2, -4, -6, -7, -8, -9, -10, -11, -12, -13, -16 and -19. After 10 days of extrinsic incubation at 23.5 degrees C, of the 13 serotypes used, seven were recovered from C. (Avaritia) imicola Kieffer and 11 from C. (A.) bolitinos Meiswinkel. Virus recovery rates and the mean titres for most serotypes were significantly higher in C. bolitinos than in C. imicola. In addition, BTV was recovered from three non-Avaritia Culicoides species, namely C. (Remmia) enderleini Cornet & Brunhes (BTV-9), C. (Hoffmania) milnei Austen (BTV-4) and C. (H.) zuluensis de Meillon (BTV-16). No virus could be recovered from 316 individuals representing a further 14 Culicoides species. In Culicoides species fed on blood containing similar or identical virus titres of distinct BTV serotypes, significant differences were found in virus recovery rates. The results of this study confirm the higher vector competence of C. bolitinos compared with C. imicola.     

Impacts of climate, host and landscape factors on Culicoides species in Scotland

Culicoides biting midges (Diptera: Ceratopogonidae) vector a wide variety of internationally important arboviral pathogens of livestock and represent a widespread biting nuisance. This study investigated the influence of landscape, host and remotely-sensed climate factors on local abundance of livestock-associated species in Scotland, within a hierarchical generalized linear model framework. The Culicoides obsoletus group and the Culicoides pulicaris group accounted for 56% and 41%, respectively, of adult females trapped. Culicoides impunctatus Goetghebuer and C. pulicaris s.s. Linnaeus were the most abundant and widespread species in the C. pulicaris group (accounting for 29% and 10%, respectively, of females trapped). Abundance models performed well for C. impunctatus, Culicoides deltus Edwards and Culicoides punctatus Meigen (adjusted R(2) : 0.59-0.70), but not for C. pulicaris s.s. (adjusted R(2) : 0.36) and the C. obsoletus group (adjusted R(2) : 0.08). Local-scale abundance patterns were best explained by models combining host, landscape and climate factors. The abundance of C. impunctatus was negatively associated with cattle density, but positively associated with pasture cover, consistent with this species' preference in the larval stage for lightly grazed, wet rush pasture. Predicted abundances of this species varied widely among farms even over short distances (less than a few km). Modelling approaches that may facilitate the more accurate prediction of local abundance patterns for a wider range of Culicoides species are discussed.     

Evaluation of housing as a means to protect cattle from Culicoides biting midges, the vectors of bluetongue virus

The housing of animals at night was investigated as a possible means of protecting them from attack by Culicoides biting midges (Diptera: Ceratopogonidae), the vectors of bluetongue. Light-trap catches of Culicoides were compared inside and outside animal housing, in the presence and absence of cattle. A three-replicate, 4 × 4 Latin square design was used at four farms in Bala, north Wales, over 12 nights in May and June 2007, and the experiment repeated in October. In the two studies, respectively, >70 000 and >4500 Culicoides were trapped, of which 93% and 86%, respectively, were of the Culicoides obsoletus group. Across the four farms, in May and June, the presence of cattle increased catches of C. obsoletus by 2.3 times, and outside traps caught 6.5 times more insects than inside traps. Similar patterns were apparent in October, but the difference between inside and outside catches was reduced. Catches were strongly correlated with minimum temperature and maximum wind speed and these two variables explained a large amount of night-to-night variation in catch. Outside catches were reduced, to a greater extent than inside catches, by colder minimum temperatures and higher maximum wind speeds. These conditions occur more frequently in October than in May and June, thereby suppressing outside catches more than inside catches, and reducing the apparent degree of exophily of C. obsoletus in autumn. The results suggest that the risk of animals receiving bites from C. obsoletus is reduced by housing at both times of year and the benefit would be greatest on warm, still nights when outside catches are at their greatest.     

Vector competence of Culicoides bolitinos and C. imicola for South African bluetongue virus serotypes 1, 3 and 4

Abstract .The susceptibility of field-collected Culicoides bolitinos to infection by oral ingestion of bluetongue virus serotypes 1, 3 and 4 (BLU 1, 3 and 4) was compared with that of field-collected C. imicola and laboratory reared C. variipennis sonorensis . The concentration of the virus per millilitre of bloodmeal was 10^5.0 and 10^6.0TCID₅₀ for BLU 4 and 10^7.2TCID₅₀ for BLU 1 and 3. Of 4927 C. bolitinos and 9585 C. imicola fed, 386 and 287 individual midges survived 10 days extrinsic incubation, respectively. Midges were assayed for the presence of virus using a microtitration assay on BHK-21 cells and/or an antigen capture ELISA. Infection prevalences for the different serotypes as determined by virus isolation ranged from 22.7 to 82.0% in C. bolitinos and from 1.9 to 9.8% in C. imicola; infection prevalences were highest for BLU 1, and lowest for BLU 4 in both species. The mean log₁₀ TCID₅₀ titre of the three BLU viruses per single fly was higher in C. bolitinos than in C. imicola . The results suggested that C. bolitinos populations are capable vectors of the BLU viruses in South Africa. A high correlation was found between virus isolation and ELISA results for the detection of BLU 1, and less for BLU 4; the ELISA failed to detect the presence of BLU 3 in infected flies. The C. v. sonorensis colonies had a significantly lower susceptibility to infection with BLU 1, 3 and 4 than C. bolitinos and C. imicola . However, since infection prevalence of C. v. sonorensis was determined only by ELISA, this finding may merely reflect the insensitivity of this assay at low virus titres, compared to virus isolation.     

Protection of livestock against bluetongue virus vector Culicoides imicola using insecticide‐treated netting in open areas

The protection of livestock against Culicoides species (Diptera: Ceratopogonidae) using physical barriers or chemically treated barriers is difficult owing to the small size of these biting midges and animal welfare concerns associated with the reduction of air flow. Culicoides imicola Kieffer is the main bluetongue virus vector in the Mediterranean basin, including the southern Iberian peninsula, where livestock is mainly housed in open pens or sheds which offer no physical protection against C. imicola. In this study we assessed the efficacy of surrounding yearling ewe pens with a canvas barrier or a cypermethrin‐treated canvas barrier in reducing the entry of Culicoides spp. and C. imicola. Analyses were based on comparisons of Culicoides catches in traps in pens with and without barriers, and in traps located outside pens. Although there was no clear reduction in the abundance of Culicoides other than C. imicola in pens with either barrier, the C. imicola presence was markedly reduced by the insecticide‐treated barrier compared with the untreated barrier; the latter did not reduce the abundance of this species in pens. Estimates of the protection conferred against C. imicola by the treated barrier differed depending on whether catch comparisons were based on outside traps or on traps located inside no‐barrier pens. The results suggest that the use of insecticide‐treated barriers may reduce contact between livestock and C. imicola in open areas or sheds. More research is necessary to assess the degree of protection as a function of barrier height, C. imicola abundance, and the size of the area to be protected.     

Replication of live-attenuated vaccine strains of bluetongue virus in orally infected South African Culicoides species

Field-collected South African Culicoides (Diptera, Ceratopogonidae) were fed on sheep blood containing 16 live-attenuated vaccine strains of bluetongue virus (BTV) comprising serotypes -1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -16 and -19. After 10 days extrinsic incubation at 23.5 degrees C, 11 and seven of the 16 BTV serotypes used were recovered from Culicoides (Avaritia) imicola Kieffer and Culicoides (A.) bolitinos Meiswinkel, respectively. One serotype was also recovered from Culicoides (Remmia) enderleini Cornet & Brunhes. Bluetongue virus recovery rates and the mean titres for most serotypes were significantly higher in C. bolitinos than in C. imicola. Significant differences were found in virus recovery rates from Culicoides species fed on blood containing similar or identical virus titres of different BTV serotypes. In addition, we demonstrated that a single passage of live-attenuated BTV-1, -2, -4, -9 and -16 through the insect vector, followed by passaging in insect cells, did not alter its infectivity for C. imicola and that the oral susceptibility of C. imicola to the attenuated vaccine strains of BTV-1, -4, -9 and -16 remained similar for at least three consecutive seasons.     

Recovery rates of bluetongue virus serotypes 1, 2, 4 and 8 Spanish strains from orally infected Culicoides imicola in South Africa

Bluetongue (BT) is an infectious disease of ruminants that has spread northwards in Europe during the last decade. The aetiological agent of the disease is an arbovirus [bluetongue virus (BTV)] that belongs to the genus Orbivirus (family Reoviridae). The virus is transmitted by certain species of biting midge within the genus Culicoides (Diptera: Ceratopogonidae). Information on the vector status of the Culicoides species in a specific area will be essential to predict the risk for BTV incursion. Field-collected Culicoides (Avaritia) imicola Kieffer from South Africa were fed on blood containing several Spanish isolates of BTV. Despite the high virus concentrations in the bloodmeal (5.1-6.4 log(10) TCID(50) /mL of blood), virus was recovered from <1% of midges assayed after incubation. Virus concentrations >2.5 log(10) TCID(50) /midge in individual infected C. imicola suggest virus replication with possible risk for transmission to susceptible vertebrate hosts in the field for at least two of the serotypes assayed (BTV-1 and BTV-2). A third serotype (BTV-4) was very close to the estimated threshold for transmission. The relatively low to near refractory status of C. imicola compared with other vector species such as Culicoides bolitinos supports previous results, indicating that Culicoides species other than C. imicola may play a more important role in the epidemiology of BTV.     

The susceptibility of Culicoides imicola and other South African livestock-associated Culicoides species to infection with bluetongue virus serotype 8

In 2006, a strain of bluetongue virus serotype 8 (BTV-8) of sub-Saharan origin was responsible for the first outbreaks in recorded history of clinical bluetongue disease (BT) in northern Europe. In this study, we examine the oral susceptibility of Culicoides (Avaritia) imicola Kieffer (Diptera: Ceratopogonidae) and other livestock-associated Culicoides species from southern Africa to infection with several strains of BTV-8. Following feeding using an artificial membrane-based method and incubation, virus was found in <1% of C. imicola individuals tested. Higher rates of susceptibility were found, however, for a variety of other South African species, including Culicoides (Avaritia) bolitinos Meiswinkel. Although these results do not preclude the role of C. imicola as a vector of BTV-8, its low susceptibility to BTV indicates that other less abundant Culicoides species may have the potential to play decisive roles in the epidemiology of this virus and should not be excluded from risk assessment studies.     

Geographical and seasonal distribution of the bluetongue virus vector, Culicoides imicola, in central Italy

Following the first incursion of bluetongue virus (BTV) into Italy, the geographical and seasonal distribution of the biting midge Culicoides imicola Kieffer (Diptera: Ceratopogonidae), the main vector of BTV and African horse sickness virus, was investigated in two regions of central Italy (Lazio and Tuscany). Surveillance of Culicoides was carried out between July 2001 and December 2002 using light traps: 1917 collections were made in 381 trap sites, well distributed across both regions. During the survey, bluetongue outbreaks were recorded in both regions. Culicoides imicola was found in 89 (23%) trap sites, distributed fairly continuously along the whole western coastline, between 41.2697 degrees N and 44.05724 degrees N. It was found only occasionally inland and usually in low abundance, with catches of more than 1000 specimens per night found in only two sample sites and 74% of catches numbering fewer than 10 specimens. Adults were caught from March to mid December, with peaks ranging from the end of August to mid November. The coastal distribution and the presence of only few sites with year-round records of adult vectors suggests that colonization may have occurred recently, by passive wind-dispersal from external source areas (Sardinia and Corsica). Alternatively, the species may occur in established, previously undetected, autochthonous populations that are limited from extension inland and northern-ward within Lazio and Tuscany by cool winter temperatures.     

Indoor and outdoor winter activity of Culicoides biting midges,vectors of bluetongue virus,in Italy

Indoor and outdoor winter activity of Culicoides spp. (Diptera: Ceratopogonidae) in central Italy was investigated in order to evaluate whether indoor activity might account for the overwintering of bluetongue virus, as has been hypothesized by some authors. Weekly Culicoides collections were performed at three farms over three consecutive winter seasons. At each farm, two black‐light traps were operated simultaneously, indoors and outdoors. Culicoides were identified using both morphological and molecular means. The Culicoides obsoletus group accounted for 98.2% of sampled specimens. Within this group, C. obsoletus s.s. accounted for 56.8% and Culicoides scoticus for 43.2% of samples. Nulliparous, parous and engorged females were caught throughout the entire winter, both indoors and outdoors. At times, indoor catch sizes outnumbered outdoor collections. A significant inverse correlation was found between minimum temperature and the proportion of indoor Culicoides of the total midge catch, thus indicating that lower outdoor temperatures drive Culicoides midges indoors. High rates of engorged females were recorded indoors, possibly as the result of the propensity of C. obsoletus females to feed indoors. Higher proportions of parous females were found in indoor than in outdoor catches, indicating higher survival rates indoors and, consequently, higher vectorial capacities of midges sheltering indoors compared with those remaining outdoors.     

Rates of bluetongue virus transmission between Culicoides sonorensis and sheep

Abstract.  Two experiments were undertaken to estimate the transmission rates of bluetongue virus (BTV) serotype 1 between a biting midge vector, Culicoides sonorensis (Wirth & Jones) (Ceratopogonidae), and a natural host, sheep. In an experiment to measure the transmission rate from vector to host (V→H), six batches of one, five and 20 intrathoracically infected midges were fed on a total of 18 bluetongue (BT)-naïve sheep. The sheep were then monitored for 21 days for clinical signs of BT, viraemia and antibody response. All sheep fed on by five or 20 midges and five of six sheep fed on by just one midge showed signs of BT, were viraemic and developed antibody. The sixth sheep fed on by a single infected midge did not show signs of BT or have detectable viraemia; it did, however, develop a weak antibody response. A bite from a single infected midge is therefore able to transmit BTV to naïve sheep with 80–100% efficiency. Sheep fed upon by larger numbers of infected midges took less time to reach maximum viraemia and developed stronger antibody responses. Sheep exposed to greater amounts of BTV in feeding midges developed a higher level of viraemia and stronger antibody responses. In a second experiment to measure the transmission rate from host to vector (H→V), batches of up to 500 uninfected female C. sonorensis fed every 1–2 days on two experimentally infected sheep during the course of infection. Of 3929 engorged midges that were individually titrated after surviving the extrinsic incubation period, only 23 (0.6%) were infected with BTV. Viraemia in the sheep extended for up to 19 days post-inoculation. No infected midges, however, were detected from 14 days post-infection.     

Culicoides aspirated from cattle in Costa Rica, Honduras, Panama and Puerto Rico, and their role as potential vectors of bluetongue viruses

Abstract. In 1991, as part of an epidemiological study of bluetongue viruses (BTV) in the Central American and Caribbean region, eight farms located in Costa Rica, Honduras, Panama and Puerto Rico were sampled for Culicoides spp. attacking cattle. Using cattle bait, 3884 biting midges were collected with an electric aspirator during both crepuscular periods. The predominant species captured was Culicoides insignis Lutz (95%), followed by C.furens (Poey) (3.4%), C.filarifer Hoffman/ C.ocumarensis Ortiz (0.9%), C.lahillei (Iches) (0.7%), C.arubae Fox and Hoffman (<0.1%) and C.gorgasi Wirth and Blanton (<0.1%). Blood-engorged specimens from some of these species were collected and comprised: 18% of all C.insignis , 36% of C.furens , 37% of filarifer/ocumarensis and 25% of C.lahillei. No engorged C.arubae or C.gorgasi were caught. These results confirm earlier findings pointing to C.insignis, C.furens and C.filarifer/ ocumarensis as potential vectors of BTV in the region.     

Vector competence of selected South African Culicoides species for the Bryanston serotype of equine encephalosis virus

Equine encephalosis virus (EEV) was recognized and described in the Republic of South Africa in 1967 and subsequent serological studies have shown this orbivirus to be both widespread and prevalent in southern Africa. In the present study it was shown that wild-caught Culicoides (Avaritia) imicola Kieffer (Diptera: Ceratopogonidae) can become infected with and permit the replication of the Bryanston serotype of EEV following membrane-feeding on infective blood containing 5.0 log10 plaque-forming-units (PFU)/ml. The mean prevalence of Bryanston virus infection in C. imicola after 10 days extrinsic incubation at 23.5 degrees C was 22.3% (23/103). The mean infectivity of Bryanston virus in the infected C. imicola increased from 1.3 log10 PFU/midge, in insects assayed immediately after feeding on the blood-virus mixture, to 2.6 log10 PFU/midge in insects assayed after incubation. The virus concentration in individual C. imicola infected with the Bryanston serotype of EEV ranged from 0.7 to 3.6 log10 PFU/midge. Bryanston virus titres higher than 2.5 log10 TCID50, found in individual C. imicola, suggest that this species may be able to transmit this virus to susceptible hosts. Prevalence of virus infection in C. imicola was determined by PFU and microtitration assays on both BHK and Vero cells and confirmation of the Bryanston serotype of EEV was determined by plaque inhibition. No virus replication could be demonstrated in 102 C. nivosus tested after the incubation period, suggesting that not all Culicoides species are equally susceptible to Bryanston virus infection. Other Culicoides species that survived the incubation period and that were negative for the presence of Bryanston virus were C. pycnostictus (42), C. leucostictus (7), C. magnus (2), C. bolitinos (1) and C. bedfordi (1).     

Predicting potential climate change impacts with bioclimate envelope models: a palaeoecological perspective

Aim We assess the realism of bioclimate envelope model projections for anticipated future climates by validating ecosystem reconstructions for the late Quaternary with fossil and pollen data. Specifically, we ask: (1) do climate conditions with no modern analogue negatively affect the accuracy of ecosystem reconstructions? (2) are bioclimate envelope model projections biased towards under‐predicting forested ecosystems? (3) given a palaeoecological perspective, are potential habitat projections for the 21st century within model capabilities? Location Western North America. Methods We used an ensemble classifier modelling approach (RandomForest) to spatially project the climate space of modern ecosystem classes throughout the Holocene (at 6000, 9000, 11,000, 14,000, 16,000, and 21,000 YBP) using palaeoclimate surfaces generated by two general circulation models (GFDL and CCM1). The degree of novel arrangement of climate variables was quantified with the multivariate Mahalanobis distance to the nearest modern climatic equivalent. Model projections were validated against biome classifications inferred from 1460 palaeoecological records. Results Model accuracy assessed against independent palaeoecology data is generally low for the present day, increases for 6000 YBP, and then rapidly declines towards the last glacial maximum, primarily due to the under‐prediction of forested biomes. Misclassifications were closely correlated with the degree of climate dissimilarity from the present day. For future projections, no‐analogue climates unexpectedly emerged in the coastal Pacific Northwest but were absent throughout the rest of the study area. Main conclusions Bioclimate envelope models could approximately reconstruct ecosystem distributions for the mid‐ to late‐Holocene but proved unreliable in the Late Pleistocene. We attribute this failure to a combination of no‐analogue climates and a potential lack of niche conservatism in tree species. However, climate dissimilarities in future projections are comparatively minor (similar to those of the mid‐Holocene), and we conclude that no‐analogue climates should not compromise the accuracy of model predictions for the next century.