Big job for a tiny insect

TIME'S UP: A thriving crop of giant reeds, the target of a new biocontrol proposal. PHOTO/SUPPLIED

A battle of David and Goliath proportions may be out to break out between tiny insects and a giant weed that is becoming an increasing threat to wetlands and waterways.

The Environmental Protection Authority is calling for submissions on an application from the Northland Regional Council, on behalf of the National Biocontrol Collective, to release the arundo wasp and the arundo scale insect, as biological control agents for the giant reed (Arundo donax).

The giant reed is a leafy, woody, bamboo-like grass that grows up to five metres high and has plumes of feathery flowers in summer.

It forms in dense clumps, growing well near river and stream margins, and can threaten wetlands, block waterways and cause flooding.

It can also be a habitat for rats and possums.

It is mainly a problem in the north of the North Island, but isolated infestations can be found as far south as Queenstown.

The EPA was calling for submissions so it could consider all views about the potential risks and benefits of introducing the two insects, Dr Fiona Thomson-Carter, general manager hazardous substances and new organisms, said last week.

"The wasps lay their eggs into the stems of the giant reed, which causes a growth, or gall that stunts, and sometimes kills the stem. The scale insects suck nutrients from the stem, reducing its growth rate," she added.

The reed was thought to be native to Eurasia, and although once valued as an ornamental plant, it was now an environmental weed in a number of countries.

The wasp and arundo scale had been released successfully in the USA and Mexico, where they were beginning to have an impact.

The NRC's application was made under the Hazardous Substances and New Organisms (HSNO) Act 1996, submissions closing on November 3.

A public hearing may be held before a decision is made.