A century of classical biological control of Lantana camara: can pathogens make a significant difference?

Lantana camara L. (Verbenaceae) is a perennial woody shrub, native to the tropical and sub-tropical zones of the Americas. It is now a major weed in many regions of the Palaeotropics, invading both natural and agricultural ecosystems. It was the first weed ever targeted for classical biological control at the turn of the century, and since then 36 insect species have been released in 33 countries throughout the exotic range. Despite these efforts, control of the weed has generally been disappointing. One of the main reasons for this, is the genetic diversity of the weedy types that have invaded the exotic range following horticultural “improvement”, including crossing with other Lantana species, resulting in a species complex. Many of these cultivars have proved to be highly invasive; in Australia alone 29 are recorded. In general, the insect agents released have a restricted host range within this complex, and, in addition, the weed is able to tolerate wider climatic and geographical areas. In the last decade, evidence of a conspicuous and damaging mycobiota on lantana in the Neotropics, has tempted protagonists of biological control to consider fungi as potential agents. In Hawaii, a Septoria sp. from Ecuador was released in 1997, whilst in South Africa, neotropical isolates of Mycovellosiella lantanae (Chupp) Deighton are currently being screened. In Australia, the Department of Natural Resources, Queensland has commissioned CABI Bioscience to investigate the potential of a sub-tropical rust pathogen, Prospodium tuberculatum (Speg.) Arthur (ex Brazil). Glasshouse results show that the agent is highly host specific (50 non-target species tested), and is pathogenic to two of the major Australian biotypes (Pink and Pink-edged red). It is envisaged that this isolate will be released in Queensland in 2000. Two other pathogens show promise: Puccinia lantanae (Farlow) Lindquist and Ceratobasidium lantanae-camarae Evans, Barreto and Ellison (web-blight). Preliminary work has started on a Peruvian isolate of the rust, and initial evidence indicates that it is able to infect a wider number of weedy cultivars and it is significantly more damaging to the target plant, causing cankering and stem die-back, than Prospodium. Moreover, it would complement the supposed geographic range of Prospodium because of its tropical rather than sub-tropical origins.