27 June 2002

The Cabinet has approved a $30 million programme to attempt to eradicate the southern saltmarsh mosquito around the Kaipara Harbour, Associate Biosecurity Minister Marian Hobbs announced today.

"This exotic mosquito, a known vector of the Ross River virus, is a real nuisance and is particularly vicious and aggressive, biting during the day," Marian Hobbs said. "We have yet to have a case of New Zealand-acquired, mosquito-borne disease in this country and this eradication programme will help to keep it that way.

"We're encouraged by results from a SSM eradication programme on the North Island's east coast and we expect a similar outcome from the Kaipara programme."

Around $30 million will be spent over the next four years developing and implementing a plan to eradicate the exotic mosquito from the Kaipara area, which covers a potential habitat of 2710 hectares.

The programme will involve aerial and ground spraying, using S-methoprene, an insect growth regulator that stops the mosquito pupae hatching into adults, and the biological spray Bti.

The mosquito lays its eggs on vegetation just above the waterline but wetting is vital for the eggs to hatch. High tides, heavy rain and wind that increase the size of waves can all encourage hatching.

BACKGROUND
What is Ross River virus?
Ross River virus disease is known as epidemic polyarthritis (inflammation of the joints). Symptoms can be wide ranging, from pain and tenderness in the muscles and joints to flu-like symptoms of chills and fevers. Most people fully recover within a month of the onset of symptoms. No locally acquired cases of Ross River Virus disease have been reported. However, people carrying Ross River Virus will regularly be present in New Zealand (e.g. tourists or travellers returning from Australian states where Ross River Virus is endemic). Only mosquitoes can transmit Ross River Virus disease. It cannot spread from person to person.

What is S-methoprene?
S-methoprene is an insect growth regulator that stops the mosquito pupae hatching into adults. It has been used extensively overseas to control mosquitoes and has undergone a full health impact assessment. S-methoprene breaks down quickly in the environment and is believed to be environmentally safe for use in New Zealand. Studies of the effect on 'non-target' species in Hawkes Bay have shown no impact.

What spray is being used currently to control the mosquito in Kaipara?
Sites are being treated with the biological spray Bti -- already being used in eradication programmes in Hawke's Bay and Tairawhiti. This product has also been used extensively in control programmes in Australia, Africa, the United States and Germany. Bti has undergone a full health impact assessment and is not allergenic. It leaves no long-term residue but is not considered adequate to achieve eradication.

When and where were mosquito larvae first found in the Kaipara area?
Sampling was taken in the Kaipara Harbour area on 18 February 2001, nine days after heavy rain and high tides were reported in the area. On February 20, the Ministry of Health was told seven of the larvae found in the Rodney District of Kaipara Harbour were unconfirmed southern saltmarsh mosquito larvae. The samples were then sent to Australia for confirmation. Since then, adult mosquitoes have also been found in the area.

How big is the area of infestation in the Kaipara Harbour area?
The infested area in the Kaipara region is the largest incursion of the southern saltmarsh mosquito in New Zealand. The potential habitat is about 2710 hectares.
How much funding did the Government allocate to controlling and eradicating exotic mosquitoes in 2001?
$5-million was approved for spending over four years to eradicate the exotic mosquito in Napier, Gisborne, Mahia and Porangahau and to contain and control the spread of the mosquito in the Kaipara and Mangawhai areas. The government has now decided that the response in the Kaipara area will move to full eradication and the other eradication programmes will continue as planned.

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