Modelling the distribution and abundance of Culicoides imicola in Morocco and Iberia using climatic data and satellite imagery
Relative abundances of Culicoides imicola at 22 sites in Morocco were compared with climatic variables, altitude and the NDVI (Normalised Difference Vegetation Index, a satellite derived measure of photosynthetic activity) of the same sites. Abundances were negatively correlated with wind speed and positively correlated with the average and minimum NDVI (NDVImin). There were no significant correlations with air or soil temperatures, relative humidity, saturation deficit, rainfall, altitude or mean annual maximum or range of NDVI. The best 2-variable model, which combined wind speed and NDVImin as predictors, explained over 50% of the variance in abundance. It is suggested that wind speed affects the abundance of C. imicola by causing adult mortality while NDVImin provides a measure of the availability of C. imicola breeding sites. Data from 27 sites in Iberia yielded broadly similar results to those found in Morocco although the great abundance of C. imicola at Milfontes (Portugal) could not be accounted for. Several northern sites where the NDVImin is sufficiently high to suggest the presence of C. imicola but where it appears to be absent indicate that there may be a northern limit to the distribution of C. imicola in Iberia that is independent of NDVImin. The potential use of NDVImin to predict the distribution of outbreaks of African horse sickness was investigated using data from the 1989–1990 epizootic in northern Morocco. Within the cluster of outbreaks in Larache province is a corridor of very low NDVImin in which few or no outbreaks were reported.
KeywordsWind Speed Normalise Difference Vegetation Index Automatic Weather Station Rift Valley Fever Normalise Difference Vegetation Index Data
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- 1.Anonymous (1992) La peste équine au Maroc. Epizooties de 1989, 1990 et 1991. Données epidemiologiques et strategie de lutte. Report of the Direction de l’Elevage, Ministère de l’Agriculture et de la Reforme Agraire, Rabat, MoroccoGoogle Scholar
- 2.Baylis M, Bouayoune H, Touti J, El Hasnaoui H, Mellor PS (1998) Use of climatic data and satellite imagery to model the abundance of Culicoides imicola Kieffer, the vector of African horse sickness virus, in Morocco. Med Vet Entomol 12 (in press)Google Scholar
- 5.Braverman Y, Galun R, Ziv M (1974) Breeding sites of some Culicoides species ( Diptera, Ceratopogonidae) in Israel. Mosq News 34: 303–308Google Scholar
- 9.Edney EG (1957) The Water Relations of Terrestrial Arthropods. Cambridge University Press, CambridgeGoogle Scholar
- 14.Meiswinkel R (1989) Afrotropical Culicoides: a redescription of C. (Avaritia) imicola Kieffer, 1913 (Diptera: Ceratopogonidae) with description of the closely allied C. (A.) bolitinos sp. nov. reared from the dung of the African buffalo, blue wildebeest and cattle in South Africa. Onderstepoort J Vet Res 56: 23–39PubMedGoogle Scholar
- 15.Meiswinkel R (1995) Afrotropical Culicoides: biosystematics of the Imicola group, subgenus Avaritia (Diptera: Ceratopogonidae). With special reference to the epidemiology of African horse sickness. M Sc thesis, University of Pretoria, PretoriaGoogle Scholar
- 27.Service MW (1978) The effect of weather on mosquito biology. In: Weather and Parasitic Animal Disease. World Meteorological Organisation, Geneva. Technical Note No. 159, pp 151–167Google Scholar