Effect of diversity on eucalyptus pests

In this study it was analyzed the effect of biodiversity changes at stand level, in eucalyptus plantations, upon the abundance of herbivorous insects and their rate of mortality by specialist parasitoids. Three mature eucalyptus stands were selected to monitor the populations of the longhorned beetle Phoracantha semipunctata and to assess egg parasitism by the encyrtid Avetianella longoi. Additionally, the population of the eucalyptus weevil Gonipterus scutellatus and egg parasitism by the mymarid Anaphes nitens were monitored in two young stands, in the early infestation phase. In each stand, six plots having either a low or high biodiversity level were chosen, considering both understorey plant diversity and landscape structure, such as the presence of forest borders. Results showed that higher stand diversity did not reflect into higher rates of parasitism by specific parasitoids, namely A. longoi and A. nitens. Nevertheless, stands having higher diversity, either at vegetation or at landscape level, generally supported lower densities of herbivorous insects, a finding which might be justified by a higher pressure exerted by generalist predators.