Removal of bell miners Manorina melanophrys from Eucalyptus radiata forest and its effect on avian diversity, psyllids and tree health

The removal of a colony of bell miners Manorina melanophrys from a Eucalyptus radiata forest in Victoria, Australia resulted in an immediate influx of other species of insectivorous birds and a short-term increase in avian diversity and abundance, similar to that reported by Loyn et al. (1983). Once bell miner numbers were greatly reduced on the experimental site, the remaining individuals ceased to exhibit interspecific territoriality and eventually abandoned the site. This suggests that a critical minimum number of individuals is needed to defend a territory. Once bell miners were removed an infestation of Glycaspis sp. psyllids at the site was devoured by the invading insectivorous birds. However, once bell miners recolonised the site, the Glycaspis sp. population returned to close to its former levels. The major reduction in the number of bell miners and psyllids at the site for a period of 10 months did not lead to an improvement in tree health during the 2 1/2 years following the cull. This contrasts with earlier findings by Loyn et al. (1983). Phytophthora cinnamomi (a pathogenic fungus) was present at both the experimental and control sites suffering dieback, and may have been the primary cause of the trees' ill-health and their lack of recovery, despite the reduction in psyllid numbers at the experimental site. Our results highlight the fact that removal of bell miners from a site suffering eucalypt dieback does not guarantee the recovery of the trees, especially if other factors may be contributing to the trees' decline. (C) 1999 Elsevier Science Ltd. All rights reserved.