An adult of the moth Leuciris fimbriaria.

The moth, Leuciris fimbriaria, released to help control mimosa in the Northern Territory.

Moth joins Kakadu weed battle

After years of research, a new biological agent has been introduced in Australia's north to help bring an introduced weed menace under control.

  • 4 December 2007 | Updated 14 October 2011

The weed mimosa threatens sensitive wetlands in northern Australia and we are engaged in a biological control battle with this introduced plant species.

Under a program overseen by CSIRO, a small moth from Mexico and South America is the latest insect to join the fight.

Wetlands menace

Mimosa pigra, or the 'giant sensitive plant', is one of Australia’s 20 Weeds of National Significance.

It forms impenetrable thickets over more than 800 square kilometres of the Northern Territory.

It is a threat to Kakadu National Park and other wetland areas in tropical Australia and has already invaded north Queensland.

Where mimosa blankets the landscape, it reduces biodiversity, competes with pastures and hinders access to water.

Mimosa was introduced to Australia from tropical America in the late 1800s as a curiosity.

People were fascinated by the fact that when the leaves were touched, they folded up.

But the plant escaped from the Royal Darwin Botanic Gardens and entered the Adelaide River system in the Northern Territory.

Exhaustive testing

The Australian Government has given CSIRO Entomology permission to release the moth, Leuciris fimbriaria, from quarantine.

Mimosa covers more than 800 square kilometres of the Northern Territory.

Years of research in Central America and in quarantine in Brisbane, Australia have lead to the granting of permission to release this new agent.

The first releases were made near the Adelaide Rver in the Northern Territory in December 2004.

Caterpillars of this moth feed on the leaves of mimosa. Extensive tests showed that these caterpillars cannot feed or grow on any plant other than mimosa.

20-year battle

Ten insect species and two fungal pathogens have been released in northern Australia over almost 20 years and are now having a noticeable impact on mimosa.

Five of the insects are well established and abundant:

  • The flower-feeding weevil, Coelocephalapion pigrae
  • The twig and stem-mining moths, Neurostrota gunniella and Carmenta mimosa
  • The seed-feeding beetle, Acanthoscelides puniceus
  • The leaf feeding beetle, Chlamisus mimosae.
 
A green looper caterpillar eating mimosa leaves.

A green looper caterpillar of the moth Leuciris fimbriaria eating mimosa leaves.

 
An aerial view of a mimosa infestation in Northern Australia.

The wet tropics of Northern Australia are threatened by dense thickets of mimosa.

Integrated attack

With the current suite of agents, widespread mimosa control may still be decades away so biological control must be integrated with other control options.

We have shown that biological control agents prefer the edges of stands of the weed so integration of these with other control methods, which break up the stands, could increase the effect of the agents.

Herbicides and fire could be used to break up the stands into smaller patches of plants thus exposing more plants to insect attack.

Biocontrol agents were also more abundant on regrowth after the use of these other methods.

The search goes on in Mexico and Brazil for more agents to attack this weed.

Of particular interest are agents that will attack plants in the middle of stands.

Why biological control?

Biological control provides the most promise for controlling mimosa as chemical and physical solutions are expensive. 

And on land that is often flooded for months access for implementing these control measures can be next to impossible.

Find out more about the Mimosa biological control project.