Bug to battle pesky privet pest

The privet lace bug has just been deployed against the widespread pest shrub privet. Photo / Landcare Research

Scientists are pitting a tiny Chinese bug against a pest shrub believed to worsen respiratory problems in a world-first Waikato trial.

Privet, an evergreen pest plant widespread in the North Island and in warmer parts of the South Island, produces poisonous leaves and berries and it's suspected that its pollen irritates people, especially in urban areas.

In attempt to control privet, Waikato Regional Council recently released about 1000 privet lace bugs near Cambridge and Whenuakite on the Coromandel Peninsula, with more of the insects to be deployed elsewhere in the region later this year.

The bug adults and nymphs combat the pests by piercing and sucking the sap from the privet leaves, which damages the leaf tips and causes defoliation.

Ahead of the release, Landcare Research conducted tests to ensure the bug was safe to set free and would prove an effective biocontrol weapon.

In May, the release was approved by the Environmental Protection Agency (EPA).

"We have been fortunate to be able to ride on the coat-tails of the Americans with this project as they had already done quite extensive host testing on plants in the Oleaceae family, which includes olives, when we got interested in the project," Landcare Research scientist Dr Quentin Paynter said.

"The early indications are that the lace bug is relatively easy to rear, which is definitely a bonus."

Waikato Regional Council biosecurity officer Hamish Hodgson said it was hoped that, over the time, the bugs would multiply and reduce the density of privet in Waikato.

As privet prevented the regeneration of native species, the bug could help to bring back New Zealand fauna that had been suppressed by the pest.

Meanwhile, the EPA also recently approved the use of the Japanese honeysuckle stem beetle, which is hoped to battle privet alongside the released Honshu white admiral butterfly, which attacks the leaves of the plant.

It is expected to be released later this year.

Many so-called biocontrol agents have been released in the country to counter weeds and plant pests, and with mixed results - but some, including a beetle used deployed against ragwort and St John's wort in Waikato had been effective.

"Biocontrol agents do take time to establish, but if they breed successfully we would look to collect bugs from the initial sites and release them elsewhere in the region," Mr Hodgson said.

"Sometimes herbicides are the best and most effective way to control some pest plants. But biocontrol is cost effective, it's environmentally friendly, and it provides a long term tool for weed control."