SPATIAL AND SEASONAL DISTRIBUTION OF CULICOIDES IMICOLA IN IBERIA IN RELATION TO THE TRANSMISSION OF AFRICAN HORSE SICKNESS VIRUS

Collections of biting midges were made over 24 months from sixty sites spread across Iberia. Information on the distribution of the vector o f African horse sickness virus, Culicoides imicola, from these 3119 sa mples showed that this species was annually present across south-weste rn Spain as far as 3 degrees 53'W and throughout most of Portugal, up to 41 degrees 5'N. C.imicola was found in all areas where African hors e sickness epizootics had occurred in 1987-90 and also in areas outsid e the epizootic zones. Seasonal patterns of capture success of C. imic ola, from seventeen frequently sampled sites where the vector was pres ent, usually showed a late summer-early autumn peak. At the sites furt hest south there was a discrete peak, mostly in September or October, before and after which the numbers captured increased or decreased ste adily. At higher latitudes peak abundances occurred as early as May or as late as November, population build up was less uniform and numbers often declined rapidly after the peak was reached. Both the distribut ion and seasonal abundance patterns closely matched transmission patte rns of African horse sickness virus, which rose during late summer and caused most cases during the autumn months.