The Environmental Protection Authority (EPA) has approved the import and release of four insects to control the spread of purple loosestrife, an invasive wetland weed.

Horizons Regional Council applied to introduce the four insects in the Manawatū-Whanganui region as biocontrol agents to target different parts of the purple loosestrife plant, Lythrum salicaria.

"These insects have been used as biocontrol agents for more than 30 years in the USA and Canada, where they reduced purple loosestrife infestations by up to 90 percent," says Dr Chris Hill, General Manager, Hazardous Substances and New Organisms.

"We hope the introduction of these insects will help slow the spread of this aggressive weed in our precious wetland ecosystems, which are home to many amazing native species, as well as capturing and storing carbon."

The insects are:

- two beetles that eat the leaves of the purple loosestrife: Neogalerucella calmariensis (commonly known as the black-margined loosestrife beetle) and Neogalerucella pusilla (commonly known as the golden loosestrife beetle)

- a root-feeding weevil, Hylobius transversovittatus (commonly known as the loosestrife root weevil)

- a weevil that eats purple loosestrife flowers, Nanophyes marmoratus (commonly known as the loosestrife flower weevil).

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

It is listed in the top 100 invasive species worldwide by the International Union for Conservation of Nature (IUCN) and has been rated by the Department of Conservation as similar to old man’s beard and Japanese honeysuckle in terms of its impact on conservation land.

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.

An established plant can create over 2.5 million seeds.

"Using chemicals or manually removing this invasive plant is often challenging due to the sensitive and remote nature of wetlands. These insects are an environmentally friendlier method of controlling these plants, rather than using chemicals."

"The testing results provided to us showed these insects are highly unlikely to harm native plants or animals. There is also no risk to people."

"Purple loosestrife is well established in some regions, such as Canterbury, the West Coast, Wellington, and Manawatū-Whanganui regions with the largest populations at Lake Horowhenua. However, it has yet to spread more widely throughout the country and the release of these insects may help to stop, or dramatically slow, this infestation."

"Our panel of independent experts approved these insects for import and release following a rigorous, evidenced-based investigative process which included the consideration of public submissions and international best practice and engagement with mana whenua."

In recent years the EPA has approved other biocontrol agents for weeds such as old man’s beard, Sydney golden wattle and moth plant, amongst others.

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