A preliminary attempt to use climate data and satellite imagery to model the abundance and distribution of Culicoides imicola (Diptera : Ceratopogonidae) in southern Africa

Abstract

Abundances of Culicoides imicola, the insect vector of several livestock viruses, including bluetongue and African horse sickness, were recently published for 34 sites in southern Africa, together with associated climate data. Here, these data are analysed statistically in combinationwith certain satellite-derived variables, with the aim of developing predictive models of C. imicola abundance. Satellite-derived variables were the land surface temperature (LST, a measure of temperature at the earth's surface) and the normalised difference vegetation index (NDVI, a measure of photosynthetic activity). Two models were developed: (1) climatic variables only and (2) satellite-derived and climatic variables. For model the best model used a single predictor variable (the mean daily minimum temperature) only, and accounted for nearly 34 % of the variance in C. imicola abundance. Two variable climatic models did not performsignificantly better. For model II, the best 1-variable model used the annual minimum LST as a predictor of C. imicola abundance, and accounted for nearly 40%of the variance in C. imicola abundance. The best 2-variable model, which gave significantly better fit than the 1-variable model, combined the minimum LST and minimum NDVI as predictors of C. imicola abundance, and accounted for nearly 67 % of variance. A map of predicted C. imicola abundances is produced on the basis of this 2nd model which, despite some anomalies, agrees largely with what is currently known of the prevalence of C. imicola in the region.