Distribution and Abundance of Bluetongue Vectors in Sardinia: Comparison of Field Data with Prediction Maps

Abstract

Following the spread of Bluetongue virus (BTV) in many Mediterranean countries during the last 5 years, presence of the main BTV vector, Culicoides imicola Kieffer (Diptera: Ceratopogonidae), was recorded in the region, including the island of Sardinia where the first BT epidemic originally started in the year 2000. Several models were also designed based on climate variables and satellite imaging in order to predict the presence and abundance of BTV vectors across Europe. A 3 years entomological survey (2001-2003) was conducted in the southern part of Sardinia confirming the widespread presence of C. imicola. However, substantial differences in terms of relative abundance were observed between field data and prediction maps based on satellite-derived climate variables. Distribution of other potential BT vectors, belonging to Culicoides obsoletus Meigen and Culicoides pulicaris Linnaeus groups was also not congruent with model-based predictions. These results stress the need of taking into account additional environmental factors (such as soil type, land usage, etc.) and local microclimatic conditions, especially related to breeding site requirements of Culicoides species, in order to predict the presence and abundance of BT vectors and to design reliable prediction maps on a local scale.

An Updated Checklist of theCulicoidesLatreille (Diptera: Ceratopogonidae) of Sardinia (Italy), and Seasonality in Proven and Potential Vectors for Bluetongue Virus (BTV)

“…It occurred along the coast (Olmedo) between late August and October, while inland (Musei and Zuri) it generally appeared later toward October to November; its seasonality at these three sites is shown in Fig. 2 and is in agreement with data obtained by Pili et al (2006) in southern Sardinia. With reference to the relative abundance of C. imicola, 81.32% of the specimens came from coastal Olmedo whereas 7.84% and 10.84% came, respectively, from inland Musei and Zuri.…”

“….sandiness and clayiness." This was reiterated subsequently by Pili et al (2006) whose field data for C. imicola also did not match the predictions made in earlier studies (Tatem et al 2003); they stressed that the extremely dry Mediterranean summers induced widespread shrinkage in potential breeding sites, to the point where these were almost wholly restricted to, for example, moist patches of soil surrounding leaking animal drinking troughs as had been documented earlier on Cyprus (Mellor and Pitzolis 1979) and elsewhere on Sardinia (Foxi and Delrio 2010).…”

“…Subsequently, Pili et al (2002Pili et al ( , 2006 reported 25 species from southern Sardinia in the provinces of Carbonia-Iglesias, Medio Campidano and Cagliari; however, some of the species were misidentified as will be discussed below. These authors reported C. imicola as the second most-abundant species, representing 35% of all Culicoides collected, and displayed peaks of major abundance between August and November.…”

Use of high spatial resolution satellite imagery to characterize landscapes at risk for bluetongue

“…Predictions from the only model taking into account Corsican entomological data are in good agreement with the observed vector distribution at the low spatial resolution of the study 2 . Nevertheless, to reveal local contrasts in distribution patterns of BT, additional fine scale analyses are necessary [37].…”

Opinion of the Scientific Panel on Animal Health and Welfare (AHAW) on request from the Commission on bluetongue vectors and vaccines

“…These outcomes show the need of taking into account additional environmental factors (such as soil type, land usage, etc.) and local microclimatic conditions, especially related to breeding site requirements of Culicoides species, in order to predict the presence and abundance of BT vectors and to design reliable prediction maps on a local scale (Pili et al, 2006;Tatem et al, 2003).…”