Lasius brunneus (Formicidae Formicinae) and Stomaphis quercus (Aphidoidea Aphididae): trophobionts harmful to cork oak forest in Sardinia (Italy)

In 2010 and 2011, we studied the biology, behaviour, harmfulness and distribution of the population of L. brunneus and S. quercus in cork oak forests in Sardinia. During their life cycle, the two trophobionts benefit from the protection provided by the cork bark. In particular, the aphid undergoes a monoic holocycle, spending much of the year inside the ant nest. Our investigations on the distribution of infested trees suggested that they are grouped into clusters, even though we occasionally found cork oaks (especially large ones) colonized by the formicid without any attacks on the surrounding trees. The ant also digs its nests in the female cork, damaging the production, and its infestations involved up to 20% of the cork oaks. The distribution of the two species was limited to some cork oak forests in the central and north-eastern parts of Sardinia between 450 and 780 m a.s.l. where the climatic conditions are typical of the cold subzone of Lauretum type II with summer drought, according to Pavari’s phytoclimatic classification.