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.

[1]  P. Rao,et al.  Relation between root zone soil moisture and normalized difference vegetation index of vegetated fields , 1993 .

[2]  P. Mellor,et al.  Observations on breeding sites and light-trap collections of Culicoides during an outbreak of bluetongue in Cyprus. , 1979 .

[3]  R. Capela,et al.  Spatial and seasonal distribution of Culicoides imicola in Iberia in relation to the transmission of African horse sickness virus , 1997, Medical and veterinary entomology.

[4]  D. Rogers,et al.  Mortality rates and population density of tsetse flies correlated with satellite imagery , 1991, Nature.

[5]  B. Wood,et al.  Estimating high mosquito-producing rice fields using spectral and spatial data , 1992 .

[6]  R. Meiswinkel.  Discovery of a Culicoides imicola-free zone in South Africa: preliminary notes and potential significance. , 1997, The Onderstepoort journal of veterinary research.

[7]  P. Mellor,et al.  The spatial and seasonal distribution of African horse sickness and its potential Culicoides vectors in Morocco , 1997, Medical and veterinary entomology.

[8]  R. Meiswinkel.  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. , 1989, The Onderstepoort journal of veterinary research.

[9]  T. Gibson.  Weather and parasitic animal disease , 1978 .

[10]  P. A. Schultz,et al.  Global correlation of temperature, NDVI and precipitation , 1993 .

[11]  D J Rogers,et al.  Monitoring trypanosomiasis in space and time , 1993, Parasitology.

[12]  A. Walker.  Seasonal fluctuations of Culicoides species (Diptera: Ceratopogonidae) in Kenya , 1977 .

[13]  S. Hay,et al.  Predicting the distribution of tsetse flies in West Africa using temporal Fourier processed meteorological satellite data. , 1996, Annals of tropical medicine and parasitology.

[14]  Baylis,et al.  Use of climatic data and satellite imagery to model the abundance of Culicoides imicola, the vector of African horse sickness virus, in Morocco , 1998, Medical and veterinary entomology.

[15]  Y. Braverman.  Characteristics of Culicoides (Diptera, Ceratopogonidae) breeding places near Salisbury, Rhodesia , 1978 .

[16]  B. Wood,et al.  Spectral and spatial characterization of rice field mosquito habitat , 1991 .

[17]  F. Davies,et al.  A preliminary survey of the epidemiology of bluetongue in Kenya , 1971, Journal of Hygiene.

[18]  R. Capela,et al.  Preliminary note on the distribution and ecology of Culicoides imicola in Portugal , 1993, Medical and veterinary entomology.

[19]  S I Hay,et al.  Remotely sensed surrogates of meteorological data for the study of the distribution and abundance of arthropod vectors of disease. , 1996, Annals of tropical medicine and parasitology.

[20]  C. Tucker,et al.  Detection of Rift Valley fever viral activity in Kenya by satellite remote sensing imagery. , 1987, Science.

[21]  C. Tucker,et al.  Use of weather data and remote sensing to predict the geographic and seasonal distribution of Phlebotomus papatasi in southwest Asia. , 1996, The American journal of tropical medicine and hygiene.

[22]  M. Thomson,et al.  The ecology of malaria--as seen from Earth-observation satellites. , 1996, Annals of tropical medicine and parasitology.

[23]  D J Rogers,et al.  Distribution of tsetse and ticks in Africa: past, present and future. , 1993, Parasitology today.

[24]  S. Randolph,et al.  Climate, satellite imagery and the seasonal abundance of the tick Rhipicephalus appendiculatus in southern Africa: a new perspective , 1993, Medical and veterinary entomology.

[25]  P. Sellers.  Canopy reflectance, photosynthesis and transpiration , 1985 .

[26]  M Daniel,et al.  Using satellite data to forecast the occurrence of the common tick Ixodes ricinus (L.). , 1990, Journal of hygiene, epidemiology, microbiology, and immunology.

[27]  C. Khamala,et al.  Larval habitats of common Culicoides Latreille (Diptera, Ceratopogonidae) in Kenya , 1976 .

[28]  S. Nicholson,et al.  The influence of soil type on the relationships between NDVI, rainfall, and soil moisture in semiarid Botswana. I. NDVI response to rainfall , 1994 .