Novel environmental factors influencing the distribution and abundance of Culicoides imicola and the Obsoletus Complex in Italy.
Bluetongue (BT) is an orbiviral disease of ruminant livestock. In Europe, the insect vectors implicated in BT virus transmission are Culicoides imicola, C. obsoletus, C. scoticus, C. pulicaris and C. dewulfi. C. imicola - an Afro-Asiatic species - is believed to account for approximately 90% of BT virus transmission; the latter four species are endemic to the Palaearctic region and are becoming increasingly important as the zone of BT virus infection in Europe moves northwards. As Culicoides distribution and ecology is critical in the spread of BT, it is essential to map their geographic ranges and to determine the ecological and climatic factors influencing their occurrence. Since 2000, more than 50 000 light trap collections have been made across Italy and the presence/absence and abundance of C. imicola ascertained; 3000 of these collections were also screened for two species (C. obsoletus, C. scoticus) of the Obsoletus Complex. To gain further insights into vector breeding habitats, spatial analysis techniques and statistical methodologies were used to investigate the association between the trap collection (municipality [polygons] and geographic point level) data and environmental and climatic variables. For the first dataset, 100 municipalities with the largest collections of C. imicola and 100 of the Obsoletus Complex, were selected and the average values of six independent climatic/environmental variables were calculated for each polygon. Factor analysis identified two principal factors explaining 84% of the total variability in climatic and environmental variables; 87.5% of trap collections were correctly classified by a discriminant analysis model. C. imicola was found to predominate in more sparsely vegetated habitats. Obsoletus Complex species were associated with a more densely vegetated habitat. For the second dataset, the presence/ absence of C. imicola at 172 sites in the region of Calabria (southern Italy) was investigated using 13 climatic, environmental and pedological variables. Factor analysis identified four factors; 89.5% of trap collections were correctly classified by a discriminant analysis model. Proximity to water-holding, clay soils was the most important factor explaining the markedly disjoint distribution of C. imicola in the 'toe' of Italy. Soil type may explain the patchy distribution of C. imicola elsewhere in Mediterranean Europe.
Conte
Annamaria
A
Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise G. Caporale, Via Campo Boario, 64100 Teramo, Italy. a.conte@izs.it
Ippoliti
Carla
C
Savini
Lara
L
Goffredo
Maria
M
Meiswinkel
Rudy
R