USING A VEGETAL INDICATOR TO CARTOGRAPHY THE POPULATIONS OF AN EXOPHILE TICK ON THE SCALE OF A COUNTRY - THE EXAMPLE OF IXODES-RICINUS, A VECTOR OF LYME-BORRELIOSE IN FRANCE

In Western Europe, Ixodes ricinus has been recognized as the vector of several animal and human diseases. The last discovered nosological entity linked with that species is Lyme Borreliosis, whose repartition is to date badly known. It then becomes important to have a comprehensive view of the vector distribution in order to know what areas are propitious to the disease. The tick is an exophile species and lives more particularly in wooded areas. For mapping the species in France, we have conceived a method L using the different vegetation types as ecological indicators, each << series >> having homogeneous environmental conditions. The successive steps in the accomplishment of the study (from the zoning of the territory to the tick sampling) are presented here (Use of small and medium scale vegetation maps, fixing the forest stations to be prospected, standardization of the flagging technique). Some results are analysed here in order to give an idea and the limits of the method. In this purpose, the authors point out the results obtained in two different areas. In South-Western France, the vegetation series can be easily distinguished and are largely variable from one area to another. In the present study, the tick frequencies are also proved to be varying from one << series >> to an other. In this case, the vegetation can be considered as an efficient indicator. The acarological data are obviously in connection with the ecological variability of the territory. As regard of Brittany (North-Western, France) because the homogeneity and uniformity of the area, the vegetation series cannot be distinguished continuously. So the use of the vegetal indicator from the reason that has been exposed, can be thought of little interest.