EPA Approves Insect Quartet To Stop Wetland Invader

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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