Bev Clarkson (right) with her tradescantia team in Northland. Image by Katrina Hansen, Northland Regional Council.
Bev Clarkson (right) with her tradescantia team in Northland. Image by Katrina Hansen, Northland Regional Council.

Brazilian beetles could help control a common weed and regenerate native forest, according to a recent report led by Manaaki Whenua – Landcare Research.

A three-year Northland study investigated whether forests invaded by tradescantia (Tradescantia fluminensis) could be managed by releasing three species of beetle, which naturally graze on the weed.

Tradescantia, also known as ‘wandering Willie’, commonly forms dense layers across forest floors – smothering native seedlings and preventing forest regeneration. It can be cleared by hand, but this is labour- and time-intensive.

In the report, project lead Dr Bev Clarkson (Manaaki Whenua – Landcare Research) says the three beetle species eat different parts of the plant, which is why they wanted to release them at the same time.

“The beetles Neolema ogloblini (which feeds on the leaf); Lema basicostata (stem); and Neolema abbreviata (tip) were sourced from Brazil. Following rigorous host-range testing that indicated they were safe to release in New Zealand, they were approved for release by the Environmental Risk Management Authority (ERMA) of the New Zealand Government,” Bev says.

At the end of the three-year study, the team found the beetles had reduced the amount of tradescantia in the trial plots and increased the number of woody seedlings that were present.

Bev says “Although the experiment needs to continue for several years before noticeable ecological benefits are achieved, results so far provide early promise of the use of biocontrol beetles in slowing or reversing biodiversity decline in floodplain forest remanants.”

As part of the study, the team has produced best-practice guidelines on how to use biocontrol beetles to control tradescantia. To read these in the full report click here.

This study was a collaborative project between the BioHeritage Challenge, Manaaki Whenua – Landcare Research Wetland Ecosystems project, Living Water and Wairua River Catchment.

Tradescantia leaf beetle (Neolema ogloblini). Image by Bradley White, Manaaki Whenua

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