CLASSIFICATION TREE METHODS FOR ANALYSIS OF MESOSCALE DISTRIBUTION OFIXODES-RICINUS (ACARI, IXODIDAE) IN TRENTINO, ITALIAN ALPS

Cases of Lyme disease and tick-borne encephalitis were recognized rece ntly in the Province of Trento, Italian Alps. Assessment of areas of p otential risk for these tick-borne diseases is carried out by a model based on classification and regression trees (CART), using both discre te and continuous variables. Data on bodes ricinus (L.) occurrence res ulted from extensive sampling carried out by standard methods in 99 si tes over an area of approximate to 2,700 km(2) in the Province of Tren to. A series of environmental parameters were recorded from each site and population densities of roe deer, Capreolus capreolus (L.), were c onsidered. The CART model discriminates 2 variables that appear to hav e the greatest effect on the mesoscale occurrence of ticks: altitude a nd geological substratum, with a drastic decrease of tick frequency ab ove an altitude of approximate to 1,100 m and on volcanic substrata. T he model is effective in identifying the mesoscale areas at greater po tential risk, with a relatively low sampling effort.