Introduction The biting midge Culicoides imicola (Diptera: Ceratopogonidae) is found in sub-Saharan Africa (24), North Africa (3, 23, 51) and southern Asia (55). The species is also found in parts of Europe, including south-western Iberia (46) and the Greek islands of Lesbos (9), Rhodes (8), Chios, Kos, Leros and Samos (M. Patakakis, personal communication). In addition, the range of the insect in Europe appears to be expanding. In 1999, C. imicola was discovered for the first time in mainland Greece, in the prefectures of Thessaloniki, Khalkidhiki, Larisa and Magnisia (M. Patakakis, personal communication), while in 2000, the species was detected for the first time in Italy, in the regions of Sardinia, Sicily, Calabria and Tuscany (M. Goffredo, personal communication; P . Scaramozzino, personal communication) and in France, on the island of Corsica (39). Culicoides imicola is a vector of several arboviruses of livestock, including bluetongue virus (BTV), which infects ruminants, and African horse sickness virus (AHSV), which infects equids. The diseases caused by these viruses, bluetongue (BT) and African horse sickness (AHS), are of major international concern and are therefore classified as List A diseases by the Office International des Epizooties (OIE). Although BT and AHS are not endemic in Europe, epidemics occur periodically in the south (Table I). During the period from 1998 to 2000, BT has occurred in several countries in the Mediterranean Basin, resulting in the loss of over 100,000 sheep (32, 34, 35, 36, 37, 39, 40, 41, 42, 43). Culicoides imicola has been implicated as the principal vector species in the outbreaks of BT and AHS in Europe (28, 44), with the exception of the outbreaks of BT in Bulgaria and northern Greece (33), where C. imicola has not been found. Areas in which C. imicola is found are potentially at risk of BT and AHS, but discoveries of C. imicola in Europe are usually only made following outbreaks of disease. A better approach would be to determine the distribution of C. imicola in Europe in advance of disease outbreaks, so that control measures (e.g. vaccination, use of insecticides and insect repellents, Rev. sci. tech. Off. int. Epiz., 2001, 20 (3), 731-740 Using climate data to map the potential distribution of Culicoides imicola (Diptera: Ceratopogonidae) in Europe E.J. Wittmann (1) , P .S. Mellor (1) & M. Baylis (2) (1) Institute for Animal Health, Ash Road, Pirbright, Surrey, GU24 0NF, United Kingdom (2) Institute for Animal Health, Compton, Newbury, Berkshire, RG20 7NN, United Kingdom Submitted for publication: 12 February 2001 Accepted for publication: 22 August 2001 Summary Culicoides imicola , a vector of bluetongue virus and African horse sickness virus, is principally Afro-Asian in distribution, but has recently been found in parts of Europe. A logistic regression model based on climate data (temperature, saturation deficit, rainfall and altitude) and the published distribution of C. imicola in Iberia was developed and then applied to other countries in Europe, to identify locations where C. imicola could become established. The model identified three temperature variables as significant determinants of the distribution of C. imicola in Iberia (minimum of the monthly minimum temperatures, maximum of the monthly maximum temperatures and number of months per year with a mean temperature ≥ 12.5°C). The model indicated that under current conditions, the distribution of C. imicola in Spain, Greece and Italy could be extended and the vector could potentially invade parts of Albania, Yugoslavia, Bosnia and Croatia. To simulate the effect of global warming, temperature values in the model were increased by 2°C. Under these conditions, the potential spread of C. imicola in Europe would be even more extensive. Keyw ords African horse sickness – Arbovirus – Bluetongue – Climate change – Culicoides imicola – Global warming – Mapping – Model – Vector-borne diseases.