Biting rates of Culicoides midges (Diptera: Ceratopogonidae) on sheep in northeastern Spain in relation to midge capture using UV light and carbon dioxide-baited traps

Biting midges in the genus Culicoides (Diptera: Ceratopogonidae) were collected near sunset by direct aspiration from sheep in northeastern Spain to determine species-specific biting rates and crepuscular activity. Midges were also collected by UV-baited light traps and CO2-baited traps over the same period to compare species diversity and abundance using these common surveillance methods to actual sheep attack rates. Culicoides aspirated from sheep included C. obsoletus, C. parroti, C. scoticus, C. punctatus, and C. imicola. Peak host-seeking activity during the time period examined for the two most commonly collected species (C. obsoletus and C. parroti) occurred just before sunset and activity ceased within 1 h after sunset. Host attack rates near sunset averaged 0.9 midges/min for both species with maximum attack rates of 3/min for C. obsoletus and 4/min for C. parroti. For both species, approximately 35% of midges collected from the sheep were engorged, giving a maximum biting rate of 1.1/min for C. obsoletus and 1.5/min for C. parroti. Traps baited with CO2 collected fewer midges of each species relative to other collection methods. Traps baited with UV light provided a good indication of species richness but significantly underestimated the host attack rate of C. obsoletus and C. parroti while overestimating the host attack rate of C. imicola. Animal-baited collecting is critical to interpret the epidemiological significance of light trap collections used for surveillance of the midge vectors of bluetongue virus and African horse sickness virus.

Results of current surveillance of likely bluetongue virus vectors of the genus Culicoides in Catalonia, Spain

Following the outbreaks of bluetongue (BT) disease in sheep on the Balearic islands in 2000, a survey was conducted for Culicoides vectors along the eastern Catalonian cost of continental Spain where the presence of only C. obsoletus (Meigen) and C. pulicaris (Linnaeus) was known. Light-trap collections made at eight sites in 2002 yielded nine species of Culicoides, including C. imicola Kieffer (represented by a gravid female caught at Dosrius at a latitude of 41 degrees 35'N) and C. scoticus Downs and Kettle. The following season (2003), C. imicola was captured consistently at all sites and in greater numbers (maximum catch of 46) from August to November. The findings suggest that the distribution of C. imicola is extending northwards into Europe. The presence of four bluetongue vectors (C. imicola, C. obsoletus, C. pulicaris and C. scoticus) in Catalonia is of concern.

Culicoides midges in Catalonia (Spain), with special reference to likely bluetongue virus vectors

Midges of the genus Culicoides (Diptera: Ceratopogonidae) were trapped weekly from May 2001 through December 2002 on two farms in the province of Barcelona (Spain). Dosrius farm was stocked with sheep and goats whereas Bellaterra farm had only sheep. This trapping programme was carried out within the framework of an investigation into the occurrence/absence of possible vectors of bluetongue virus (BTV) in mainland Spain. A total of 30,079 Culicoides specimens were collected from 165 light trap collections, comprising nine species: C. obsoletus (Meigen), C. pulicaris (Linnaeus), C. circumscriptus Kieffer, C. newsteadi Austen, C. imicola Kieffer, C. scoticus Downes & Kettle, C. punctatus (Meigen), C. pallidicornis Kieffer and C. flavipulicaris Dzhafarov. The last five are new to Catalonia, C. pallidicornis is also new to Spain and C. flavipulicaris is new to Iberia. The seasonal occurrence of these species is described here. Of those species, C. imicola is the main BTV and African horse sickness virus (AHSV) vector in Europe, whereas species belonging to the so-called Obsoletus group (C. obsoletus and C. scoticus in our study) are considered to be potential vectors for BTV.