Biological control of Australian acacias: what you see is not what you get

Biological control of Australian acacias: what you see is not what you get
John H. Hoffmann1, Fiona A.C. Impson1,2 & Carien A. Kleinjan1
1Department of Biological Sciences, University of Cape Town, Rondebosch 7700, South Africa.
2ARC-Plant Protection Research Institute, P. Bag X5017, Stellenbosch 7600, South Africa. 

Biological control is being used against 13 species of invasive Australian acacias in South Africa with agents comprising two gall midges (Cecidomyiidae), two gall wasps (Pteromalidae), several seed beetles (Curculionidae) and a rust fungus (Basidiomycetes).  The fungus is the only agent that damages the whole plant.  The insects are all associated with the flowers and seeds on the plants.  It is 40 years since the first agent was released, the bud gall wasp Trichilogaster acaciaelongifoliae on Acacia longifolia.  The question is what has happened in the interim and have we achieved anything worthwhile with the flower and seed-feeding insects.  An overview of historic and recent events is used to show that, while the record is regrettably incomplete, there is enough evidence to show that the investment in biological control has been very worthwhile and will provide increasing benefits into the future.