Tiny beetle helps battle mimosa in tropical wetlands

The mimosa flea beetle, Nesaecrepida infuscata, has successfully negotiated host specificity testing in quarantine in Brisbane – to make sure there’s no threat to native fauna – and Biosecurity Australia and the Australian Department of Environment have now given permission for its release.

“Mimosa has been the target of biological control for many years and we now have a suite of insects busily eating stems, seeds and flowers and driving back the edges of stands,” says Dr Tim Heard, from CSIRO Entomology and the CRC for Australian Weed Management.

“Since 1983, we have released 12 insects and two fungi on mimosa in Australia and a recent study showed that the four most effective insects have reduced seed rain and soil seed banks by 90 per cent.”

Dr Heard says the mimosa flea beetle was specifically chosen to fight mimosa in the tropical wetlands because its larvae feed on mimosa roots and the soft tissues of seedlings, often killing them. Adults feed on the leaves.

These parts of the plant are relatively untouched by current agents so this beetle should put mimosa under even more pressure.

CSIRO entomologists originally found the flea beetle on mimosa in Mexico and Venezuela, the weed’s home range.

The Weeds Management Branch of the Northern Territory Government in Darwin will mass rear the beetle ready for initial releases on local infestations.

Dr Heard says in the long term mimosa management will depend on an integrated package of control methods, including biological control. Trials showed that the use of chemicals, mechanical disruption and fire did not affect agent numbers on mimosa plants, and in some cases even increased them.

Mimosa was introduced into Australia in the late 1800s as a curiosity, and escaped from the Royal Darwin Botanic Gardens into the Adelaide River system. It is now a serious weed of northern Australian wetlands and floodplains. Its potential distribution is enormous, stretching from Broome in WA to northern NSW. In 1999, it was declared one of Australia’s 20 Weeds of National Significance.

Its other common names in Australia include giant sensitive plant or giant sensitive tree.

The mimosa flea beetle research was supported by the Australian Department of the Environment’s Natural Heritage Trust, through its Defeating the Weeds Menace program.

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