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

Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise, via Campo Boario, 64100, Teramo, Italy.
Veterinary Parasitology (Impact Factor: 2.38). 12/2007; 150(4):333-44. DOI: 10.1016/j.vetpar.2007.09.021
Source: PubMed

ABSTRACT 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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Culicoides imicola is the main vector of the bluetongue virus in the Mediterranean Basin. Spatial distribution models for this species traditionally employ either climatic data or remotely sensed data, or a combination of both. Until now, however, no studies compared the accuracies of C. imicola distribution models based on climatic versus remote sensing data, even though remotely sensed datasets may offer advantages over climatic datasets with respect to spatial and temporal resolution. This study performs such an analysis for datasets over the peninsula of Calabria, Italy. Spatial distribution modelling based on climatic data using the random forests machine learning technique resulted in a percentage of correctly classified C. imicola trapping sites of nearly 88%, thereby outperforming the linear discriminant analysis and logistic regression modelling techniques. When replacing climatic data by remote sensing data, random forests modelling accuracies decreased only slightly. Assessment of the different variables' importance showed that precipitation during late spring was the most important amongst 48 climatic variables. The dominant remotely sensed variables could be linked to climatic variables. Notwithstanding the slight decrease in predictive performance in this study, remotely sensed datasets could be preferred over climatic datasets for the modelling of C. imicola. Unlike climatic observations, remote Remote Sens. 2014, 6 6605 sensing provides an equally high spatial resolution globally. Additionally, its high temporal resolution allows for investigating changes in species' presence and changing environment.
    Remote Sensing 07/2014; 6:6604-6619. · 2.62 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 1. Culicoides midges (Diptera: Ceratopogonidae) are ubiquitous on farms in the United Kingdom (UK), but little research has explored their abundance, an important determinant of disease risk. Models to explain and predict variation in their abundance are needed for effective targeting of control methods against bluetongue virus (BTV) and other Culicoides-borne diseases. Although models have been attempted at the national scale (e.g. Scotland), no investigations have taken place at a finer spatial scale. 2. Midge abundances were estimated using light traps on 35 farms in Bala, north Wales. Culicoides catches were combined with remotely sensed ecological correlates, and on-farm host and environmental data, within a GLM model. Drivers of local-scale variation were determined at the 1-km resolution. 3. Local-scale variation in abundance exhibited an almost 500-fold difference (74—33 720) between farms in maximum Obsoletus Group catches. The Obsoletus Group model explained 81% of this variance and was dominated by normalized difference vegetation index (NDVI). This is consistent with previous studies suggesting strong impacts of forest cover and vegetation activity on distribution, as well as shaded breeding site requirements. 4. The variance explained was consistently high for the Pulicaris Group, C. pulicaris and C. punctatus (80%, 73% and 74%), the other probable BTV vector species in the United Kingdom. The abundance of all vector species increased with the number of sheep on farms, but this relationship was missing from any of the non-vector models. This is particularly interesting given that none of the species concerned are known to utilize sheep-associated larval development sites. Performance of the non-vector models was also high (65—87% variance explained), but species differed in their associations with satellite variables. 5. Synthesis and application. At a large spatial scale, there is significant variation in Culicoides Obsoletus Group abundance, which undermines attempts to record their nationwide distribution in larger-scale models. Satellite data can be used to explain a high proportion of this variation and, if shown to be generalizable, they may produce effective predictive models of disease vector abundance. We recommend undertaking a prior survey for farms with high Culicoides catches within the sampling area and checking stability in catch size between seasons and years.
    Journal of Applied Ecology 02/2013; 50(1):232-242. · 4.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Culicoides imicola Kieffer and Culicoides bolitinos Meiswinkel (Diptera: Ceratopogonidae) are both of veterinary importance, being vectors of Schmallenberg, bluetongue and African horse sickness (AHS) viruses. Within South Africa, these Culicoides species show a marked difference in their abundances according to altitude, with C. imicola highly abundant in lower altitudes, but being replaced as the dominant species by C. bolitinos in cooler, high-altitude regions.
    Parasites & Vectors 08/2014; 7(1):384. · 3.25 Impact Factor


Available from
May 20, 2014