Coroebus undatus (Coleoptera: Buprestidae) sur chêne liège dans le Sud-Est de la France : estimation des dégâts, relations entre ceux-ci et certains facteurs du milieu

Coroebus undatus (Coleoptera: Buprestidae) on cork oak in southeastern France: an estimate of damage and its relationship to environmental factors. In 52 plots distributed throughout the cork oak stands (Quercus suber L) of the Maures-Esterel region in southeastern France (fig 1) 5-15 oaks were selected from those whose cork had been removed less than 1 year before. On such trees, galleries made by the late-instar larvae of the last generation of Coroebus undatus (Fabr) are clearly visible at the surface of the stripped part of the stem. On each tree, the 4 vertical lines running through the middle of the north, east, south and west sides of the stripped part of stem were divided into 50-cm long sections from soil surface, and intersections between galleries and each of these segments of lines were counted. For each tree and each plot a damage index was calculated as follows: the damage index of a tree (IA) was the mean total number of intersections per stem side counted on the first basal 1.50 m of the stem, that of a plot (IP) was the mean value of IA. IA may be considered to be roughtly proportional to the percentage of damaged stem surface (A%), ie, the ratio, expressed as a percentage, between the total surface of the galleries and the surface of the stem; both variables are approximately linked by the relationship: A % = 0.4 IA. C undatus occurred everywhere in the investigated area, but IA and IP ranged from 0 to 27.6 and 1.2 to 14.8 respectively, according to the trees and the plots (figs 2, 3). The first basal 0.50 m of stems was on average ≈ twice less damaged than the rest of their surface, while their south and west sides were slightly more damaged than the 2 others. Within plots, trees were equally damaged (same mean IA value) whatever the diameter and probably also the shade degree of their stems. Between-plot variation in IP was not explained by the mean diameter nor probably by the mean shade degree of stems. IP value tended to vary inversely with elevation, and was higher on average on southern slopes