Microbiological control programs against two Lepidoptera defoliators of cork oak in Sardinia (Italy): short- and long-term effects

Abstract: The gypsy moth, Lymantria dispar, and the tent caterpillar, Malacosoma neustrium, are the main pests of cork oak in Sardinia (Italy) and are characterized by cyclical fluctuations of their population abundance. During the years of maximum infestation, the two species can defoliate more than 60,000 hectares of cork oak forests, negatively affecting the health status of oaks and reducing plant growth and cork production. In order to reduce Lepidoptera infestations in cork oak forests, large-scale control programs based on aerial applications of Bacillus thuringiensis subsp. kurstaki (Btk) formulations have been carried out in Sardinia since 2001. The microbiological applications protected efficiently the oak foliage from the gypsy moth and the tent caterpillar. However, the long-term effectiveness of Btk against L. dispar differed depending on the gradation phase in which the bioinsecticide was applied. Lymantria dispar infestations decreased gradually in the years following Btk applications when they were done in the culmination phase, whereas applications performed in the progradation phase led to an increase in the population density after 2-3 years. These results could be useful for decision-making in control programs against L. dispar in cork oak forests and indicate that an accurate choice of timing of Btk application is necessary.