A review of the Chrysanthmoides monilifera biological control program in Australia: 1987-2005

Two subspecies of Chrysanthemoides monilifera, namely subsp. rotundata (DC.) T.Norl. (bitou bush) and subsp. monilifera (L.) T.Norl. (boneseed), have been introduced to Australia from South Africa and are now among our worst environmental weeds. A biological control program was established in 1987 to combat these two invaders. To date, six species of insects have been released on bitou bush, four of which have established. The bitou tip moth (Comostolopsis germana Prout) and bitou seed fly (Mesoclanis polana Munro) are now widely established in New South Wales and two other agents, the bitou tortoise beetle (Cassida sp.) and the bitou leaf roller ('Tortrix' sp.) are currently surviving in low numbers in New South Wales but only in the vicinity of their initial release sites. A total of six species have been released for boneseed, but despite repeated and often large releases, none of these agents have established in the field. Predation by indigenous invertebrates is suspected as being a key factor in preventing establishment of the foliage feeding agents in Tasmania, South Australia and Victoria. The leaf buckle mite, Aceria sp., is one of several additional agents being investigated for the control of boneseed; it was approved for field release in 2005. Despite the failure of several agents to establish in the field, especially on boneseed, the biological control program has delivered some successes. The pending release of the leaf buckle mite and the targeted selection of future agents specifically for boneseed should help to counteract previous setbacks.