Border wars against little nasties

New Zealand has been invaded again. CATHERINE MARSTERS reports on the constant battle to keep out foreign pests that could cost the country millions and pose health risks.

Most of them burrow, crawl or slither their way into the country by stealth.

Overseas pests with the potential to devastate the environment and the economy and cause havoc to your health are already here and more keep turning up.

In the past week, the discovery of a black widow spider and an Asian tiger mosquito have revived questions about border security.

Here are some of the biggest biosecurity threats - some thwarted, some not - which New Zealand has faced in the past few years.

MOSQUITOES

Species: Asian tiger mosquito, yellow fever mosquito, southern saltmarsh mosquito.

Origin: Australia, Asia.

Arrival: Mosquitoes hitch rides on ships and turn up in ports. Larvae and pupa cases of the Asian tiger mosquito were found at Queen's Wharf in Auckland this week. Traps have since been set at ports in Auckland, Wellington and Christchurch.

Danger: All these mosquitoes are potential carriers of a raft of unpleasant and potentially fatal diseases, including yellow fever, dengue fever and Ross River virus. Yellow fever causes flu-like symptoms and, in more advanced cases, nausea, fever, headache and muscle pain. Dengue causes fever, upset stomach and severe restlessness. If the Australian southern saltmarsh brings Ross River fever, which can cause similar health problems that last for years, thousands of people could be infected.

Status: The southern saltmarsh was discovered in Hawkes Bay in 1998 and this year in the Kaipara Harbour and at Mangawhai. In the Hawkes Bay, spraying programmes may have done the trick as none has been found for about a year.

SPIDERS

Species: Many, including redbacks from Australia, the black widow from America and a South African species known as the false katipo, which is displacing the native. Well established now is the Australian white tail.

Origin: Australia, America, South Africa and elsewhere.

Arrival: Black widows, with red blotches on the back, love to hide in bunches of Californian grapes, which New Zealand imports for the wine industry and for supermarkets. A third black widow in three months turned up this week - that's one for every one million bunches of grapes.

But MAF says about 12 a year get in by crawling into clothing and luggage and coming through airports.

Danger: Redbacks are venomous and like to hide in nooks, crannies and dark places. They prefer the outdoors but can turn up in the toilet. A bite is not usually fatal.

You are more likely to cross paths with the now common Australian white tail in the woodpile or on the wall of your house. It has a particularly nasty bite, which causes swelling. Sometimes the poison eats away flesh.

Status: Black widows are not thought to be established in NZ. Californian grapes are fumigated in the US. MAF says an audit after the spiders were found here showed there had not been a failure, but if another one turns up MAF will review the system.

Another danger from the grapes is a pest called the glassy winged sharpshooter, which has not made it into New Zealand but has decimated the Californian wine industry. The local wine industry has called for a ban on imports of Californian grapes.

MOTHS

Species: Painted apple moth, white-spotted tussock moth.

Arrival: The white-spotted tussock moth infected Auckland City's eastern suburbs in 1996 and a $12 million aerial spraying programme was launched to eradicate it.

The painted apple moth from Australia turned up in West Auckland in 1999.

Danger: The tussock moth could have wrecked our forestry industry and native beech forests if it had become established. The painted apple moth can defoliate trees and especially likes wattles.

Status: The 1996 spraying campaign on the tussock moth succeeded. A painted apple moth community advisory group has been set up and targeted aerial spraying is being discussed, along with trapping.

ANTS

Species: Argentine ant and the red imported fire ant.

Origin: South America.

Arrival: A nest of red imported fire ants was found at Auckland Airport in March, sparking a high alert, partly because it had been there for months. Argentine ants have been in the North Island for more than 10 years.

Danger: Considered one of the world's worst insect pests, red imported fire ants are tiny but aggressive, swarming and attacking together when disturbed and giving nasty stings. Their damage is very expensive. In America, they are well established and cause billions of dollars of damage a year to livestock, wildlife, property and public health. Riverbanks and playgrounds cannot be used when they are present.

The Argentine ant is not poisonous but it bites and eats just about anything. It kills other ants and insects and is a serious nuisance around the house.

Status: The fire ants' nest was treated and the ants killed. But because the nest was so old, some of the ants are feared to have flown from the nest. MAF, the Conservation Department, the Ministry of Health, the Auckland Regional Council and pest controllers are working on measures to prevent them getting established.

The Argentine ant is now widespread but a new bait from Australia may be able to control them.

SNAKES

Species: Eastern brown (Australia), Indonesian tree-pit viper, tiger snake (South Australia).

Origin: Most of the world.

Arrival: Two snakes have arrived so far this year. Five were found last year.

Danger: They bite, some are venomous and some kill. They would eat native birds and small animals.

Status: Despite several discoveries of individual live snakes, which have been caught and destroyed, New Zealand remains snake-free.

VARROA BEE MITE

Origin: Widespread around the world, apart from Australia.

Arrival: Probably up to five years ago, although it was not discovered until last year.

Danger: Attacks honey bees and their larvae, wipes out hives by killing the bees needed to pollinate pastures and crops. It has been found in many thousands of hives and is expected to cost between $400 million and $900 million in losses over the next 35 years.

Status: The Government has given up on getting rid of the mite but has committed $7.5 million to controlling it in the North Island.