An Australian pest, the eucalyptus leaf beetle, has taken up residence in New Zealand for the first time, in Whitemans Valley near Wellington.
Discovery of the beetle was made by the Katherine Mansfield Dr residents who noticed the beetle in the trees and sent it to an entomologist.
The leaf beetle, about 12mm long when adult, strips eucalyptus trees of young leaves and shoots. Its discovery has led to a comprehensive biosecurity response from the Ministry of Primary Industries which will involve two 30-minute insecticide sprays, by helicopter at least 10 days apart, over half a hectare.
"This beetle is new to New Zealand. We have never encountered this before," David Yard, Primary Industry's response team manager said.
"We are responding to eradicate it as we don't want it to be established in New Zealand.
"If we allow it to become established it would be at a huge cost impact to the country."
The beetle, native to Australia, was discovered in August and the ministry's response team has been monitoring the site since then and preparing for the aerial spraying, scheduled for April 23, depending on weather conditions.
The detection of several eggs, larvae and adult beetles indicated a breeding population may exist.
"The beetle defoliates the trees. It likes the fresh young trees," Yard said.
There are "quite a few stands of eucalyptus trees in the Whitemans Valley," he said.
Inspection of an area with a 3km radius from the located beetle had not found any more nests and the aerial spray will be limited to the known stand of 40-50 trees.
"Surveillance of the surrounding area has determined the beetles have not spread from the mall site where they were originally detected."
Yard estimated the full ministry response and eradication could cost up to $100,000 and will continue for more than a year after the helicopter spraying.
"Hopefully it will be successful but there will be no announcements (of success) and we will be investigating and monitoring the area for another year to 18 months."
It is not known how the beetle arrived, Yard said.
"We have investigated possible pathways on to the site but there doesn't seem to be any obvious source."
The spraying will only be carried out when wind conditions mean "spray drift" will be kept to a minimum.
"There are no public access points to the stand of trees to be treated (while) a creek in the spray zone will be covered during spraying," a public notice said.
Property owners have been helpful and the ministry has been in communication with several since the discovery with their searches and to explain the eradication process.
Yard said properties, and their roofs especially, will need to be hosed down after the spraying.
The aerial spray, Dominex 100 EC, contains the insecticide alpha-cypermethrin.
"It is commonly used on many insect pests (ants, spiders) in and around buildings and houses. It is also sprayed on food crops such as beans, tomatoes and sweetcorn," ministry information said.
The spray has been effective in controlling other eucalypt pests in New Zealand.
The ministry and its contractors will be on site while the eradication work is carried out "to ensure compliance with the spraying plan and the provisions of the Regional Air Quality Management Plan".
The potential impact of the (Paropsisterna beata) beetle is unknown. "It may cause moderate impact to New Zealand eucalyptus trees due to the absence of natural enemies to control the population," the information said.
The beetle is not a major pest in commercial eucalyptus plantations in Australia but some related species cause significant damage to eucalyptus species.