Felling a giant

Two insects common around the Mediterranean can now be imported into New Zealand to control the giant reed (Arundo donax), following a decision by the Environmental Protection Authority(EPA) made under the Hazardous Substances and New Organisms Act (1996).An application by Northland Regional Council to introduce the arundo galling wasp and the arundo scale insect to New Zealand has been approved.

An application by Northland Regional Council to introduce the arundo galling wasp and the arundo scale insect to New Zealand has been approved.
The giant reed is mainly found in the far north of New Zealand, but there are fears it may spread south as temperatures increase, adversely impacting on riparian and other sensitive habitats.

The committee noted that giant reed effectively grows and expands its range via a strong rhizome network. This generates large colonies of giant reed plants that directly impact the environments it invades. Giant reed negatively affects the biodiversity of insect and plant life associated with habitats where giant reed grows prolifically, and has been shown to displace endemic and endangered species in the United States of America, Mexico and the Canary Islands.

“The arundo galling wasp and arundo scale insect have been successful in curbing the vigour and abundance of giant reed stands in those habitats,” says EPA scientist Dr Clark Ehlers. “The galling wasp lays its eggs inside giant reed shoot tips, which swell as gall tissue builds up. Growing wasp larvae feed on this tissue. A single wasp can produce 20-30 offspring.”

“The arundo scale insect attacks the giant reed by puncturing plant tissue and sucking out nutrients, reducing plant growth. As the two insects’ feeding niches do not overlap, their combined impact on the giant reed can be significant,” Dr Ehlers says.

In making its assessment the committee considered various potential risks and costs, including those to the environment, human health and safety, the market economy, Māori culture and tradition, and the Treaty of Waitangi.
It noted there are no native plants closely related to the giant reed and considered the results of containment and field-tests done in the United States, Spain and New Zealand to assess the insects’ preference for the giant reed over other food sources.

The committee also noted a Landcare Research survey showing the number and diversity of insects living in and around giant reed was low. As there are no native insects closely related to those covered by the application, the chance of them hybridising is negligible, the committee found.

“The committee concluded it would be beneficial to establish a population of the two insects, and that neither would be likely to cause adverse effects in the New Zealand environment. It also noted it was highly improbable that the arundo galling wasp or arundo scale insect would form undesirable self-sustaining populations,” Dr Ehlers said.

For the committee’s decision see: http://www.epa.govt.nz/search-databases/HSNO%20Application%20Register%20Documents/APP202887_APP202887_Decision_FINAL.pdf

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