The gypsy moth, Lymantria dispar (L.), and the tent caterpillar, Malacosoma neustrium (L.), are the main cork oak, Quercus suber L., pests in the Mediterranean area and cause complete defoliation in large forest districts. In order to control infestations, large scale aerial applications of insecticides based on Bacillus thuringiensis subsp. kurstaki (Btk) have been carried out in Sardinia (Italy) since 2001. This paper evaluated the frequency of outbreaks in forest districts with varying homogeneity of land use, forest areas annually exposed to defoliation and the effectiveness of control programs based on Btk insecticide applications. The volume of areas annually exposed to defoliation depends on forest homogeneity, as infestations are more frequent in cork oak areas with a lower than 25% canopy cover rate. The microbiological control programme efficiently protected cork oaks from lepidopteran defoliators and caused an overall annual mean mortality of over 60%, with maximum rates of 89.9 and 98.0% for L. dispar and M. neustrium, respectively. To date, approximately 180,000 hectares of cork oak forests have been protected by spraying Btk-based insecticides.
