Page 16 - LandscapeSA Issue 106

fEATURE

Lysathia sp. a leaf-eating beetle on Parrot’s feather, an aquatic weed. The insect was the first
biological control agent brought to South Africa and was released at five sites in December 1995.
PHOTOS BY BEN MILLER.

spread of Port Jackson willow in invaded There are still several weed species for for managing biodiversity risks to native
areas. In conjunction with the pathogen, a which successful biocontrol remains elusive flora and fauna.
seed-feeding weevil reduces the numbers and remain a significant biodiversity threat.
of viable seeds released from the plant. Although >30 agents were investigated Still, it is not the only solution to these risks.
After three decades, the fungus’s impact against Lantana camara, only seven agents For many species, utilising an integrated
on the plant’s growth and development were released. None have yet to have any management approach, i.e. one that
is extremely high. Stands of Port Jackson significant impact on the density, survival incorporates more than one management
willow that would otherwise have been or spread of Lantana. In the late 1980s, option, is perhaps the most efficient
extremely dense and likely spreading, have the first biocontrol agents against Prosopis means of controlling invasive species
decreased in abundance due to the impact were released in South Africa. Only seed- populations. For others though, the use
of this fungus. feeding agents that consumed mature of a sustainable, environmentally-friendly
seeds were considered for release. Since option such as biological control cannot
Biological control is also prevalent and then, only a single agent has been released. be rivalled. Research into this field provides
effective in controlling invasive water Prosopis is regarded as a usable resource very valuable insight for managing invasive
weeds. Some water weed species are (firewood, charcoal and furniture). There are species in a global and national context.
controlled to the point where they are no considerable constraints for the escalation
longer considered a significant threat to of biocontrol against this invasive weed, About the authors
ecosystems and biodiversity. One such which remains a significant concern. Dr Candice Lyons is an Honorary Research
species is the red water fern. A weevil Associate of the Biological Sciences
released in 1997 successfully reduced weed As with most other biological disciplines, Department at the University of cape
populations to where they are no longer the success of biological control Town and an Adjunct Research Officer
considered a problem. Parrot’s feather programmes is influenced by many factors, of the Department of Ecology, Evolution
is another water weed considered to be including environmental/ biological and Environment, La Trobe University,
under complete biocontrol. A single beetle factors that impact either agent, target Melbourne.
species was deemed adequate to reduce plant or both plant and agent. For this
the infestations of this weed to within reason, and as explained above, success is Dr Alana den Breeyen is a Senior Researcher
tolerable levels, in some cases clearing never guaranteed. Biological control is an in Plant Pathology with Manaaki Whenua
entire water bodies in a matter of months. ongoing and evolving field that is valuable Landcare Research in New zealand.

Azolla filiculoides in George (before) Azolla filiculoides in George (after eight months)

14 Landscape SA • Issue 106 2021