Consultation under way on plan to release insects to combat invasive weed in Manawatū-Whanganui

The largest population of purple loosestrife in Manawatū-Whanganui is at Lake Horowhenua and the surrounding area.

An application to release insects to control an invasive wetland weed in the Manawatū-Whanganui region is now open for public feedback.

The Environmental Protection Authority (EPA) wants people’s views on Horizons Regional Council’s application to introduce four insects as biocontrol agents to target different parts of the purple loosestrife plant, Lythrum salicaria.

The insects are two beetles that eat the plant’s leaves (Neogalerucella calmariensis and Neogalerucella pusilla), a root-feeding weevil (Hylobius transversovittatus) and a weevil that eats purple loosestrife flowers (Nanophyes marmoratus).

Purple loosestrife is a bushy plant that forms high, impenetrable stands which overwhelm other plants, threatening native biodiversity and significantly impacting wetland ecosystems, the EPA said in a statement.

It is native to Europe, parts of Asia, and Australia, and was introduced to New Zealand as an ornamental herb before naturalising in the wild in the 1950s.

The plant can be found in Canterbury, the West Coast, Wellington and Manawatū-Whanganui regions, with the largest populations at Lake Horowhenua and the surrounding area.

Purple loosestrife is considered a noxious weed in the United States and Canada, where it has affected large areas of wetland ecosystems.

The two leaf-eating beetles proposed to control the weed are from Europe and Asia, while the two weevils that feed on the roots and flowers are from Eastern Europe.

“The applicant’s risk assessment includes studies that show they are highly unlikely to harm native plants or animals,” EPA hazardous substances and new organisms general manager Dr Chris Hill said.

“None of these insects bite or sting, so there is no potential risk to people.”

Horizons said the same insects had been used together as biocontrol agents in the US, where they reduced purple loosestrife infestations by up to 90 per cent in some areas within the first 10 years.

Through the public consultation process, the public and people in relevant industries can provide additional information on the risks and benefits of introducing the insects.

Submitters can provide information, make comments and raise issues to contribute to the EPA decision-making process. Submissions close at 5pm on October 17.

More information about the application is available at www.epa.govt.nz.