The painted apple moth: What, why and how

What is painted apple moth, where did it come from and how long has it been here?

Painted apple moth (Teia anartoides) is a native of Australia. It has three characteristics central to the debate on its eradication - it is a voracious feeder, a highly efficient reproducer and the female does not fly.

It was discovered in Glendene, West Auckland, in May 1999, but is likely to have arrived six months earlier, possibly in a shipping container.

What does it look like, and how big is it?

The male moth has a 2.5cm wingspan, a dark brown forewing marked with a black band and an orange hindwing with a broad black outer band. The wingless female moth is about 1cm long and is covered with thick short brown hairs - she looks like a small, brown, hairy cocoon.

The mature larva or caterpillar is about 3cm long and is covered with dense brown hairs. Four tufts of white hairs extend from its back, and a pair of black horn-like tufts projects from behind its head.

How similar is it to white-spotted tussock moth, found in East Auckland in 1996?

The two belong to the same family. The Ministry of Agriculture and Forestry estimated white-spotted tussock moth could have caused $100 million worth of damage to our forestry industry if not wiped out. For painted apple moth, the estimate is $48 million worth of damage to horticulture and forestry over the next 20 years.

The biggest difference cited by the ministry between painted apple moth and white-spotted tussock moth is that the spread of this latest invader is naturally limited because of the flightless female. But the small larva are quite mobile, hanging by long silken threads and "ballooning" when picked up by the wind.

One thing the two have in common is an impressive ability to reproduce. Like white-spotted tussock moth, painted apple moth females can lay up to 700 eggs at a time and produce several generations each year.

Why didn't they just blitz the thing when they first found it?

The ministry says it took a "conservative and responsible" approach to eliminating the pest, by ground-spraying, property surveys and removal of trees in an effort to save West Auckland residents from an aerial campaign.

How did they think they were going to get rid of it during the past two years?

The ministry has been ground spraying infested areas with Decis Forte (Deltamethrin), a synthetic chemical pesticide registered for use in New Zealand.

The use of this chemical is controversial because it is toxic to fish. Critics also argue is could be harmful to humans.

They also argue that Btk should have been used in ground spraying from the beginning because it is not as toxic and could therefore have been used more freely.

The ministry says Decis is more effective than Btk for a ground operation.

It has also been removing vegetation from the area - trees and plants the caterpillar likes to feed on such as wattle and acacia trees.

How many caterpillars and moths are there and how does that number compare with white-spotted tussock moth in 1996?

In November-December last year, up to 500 live moths were being caught in a week. Single male moths finds (the ministry has a grid of 600 traps across most of Auckland) and more serious infestations have been found in an area that stretches from Titirangi in the west to Pakuranga in the east, from Pt Chevalier in the northwest to Onehunga in the southwest.

White-spotted tussock moth infested approximately 7sq km near the ASB Stadium in Kohimarama with moth finds in three nearby suburbs.

What is Btk?

The main ingredient is a naturally occurring bacterium called Bacillus thuringiensis var kurstaki, found in soil, foliage, water and air.

But the spray has an unknown number of added ingredients which are secret for commercial reasons. It kills caterpillars by rupturing their gut.

nzherald.co.nz/environment