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Exotic mosquito Kaipara eradication's new phase


Attempts to eradicate exotic mosquito in Kaipara enter new phase

A Ministry of Health programme aimed at eradicating exotic mosquitoes which can carry a debilitating disease will move into a new phase around Kaipara Harbour tomorrow.

Mosquito growth regulator S-methoprene -- which has already been successfully used in southern saltmarsh mosquito Ochlerotatus camptorhynchus eradication programmes in Hawke's Bay and Tairawhiti -- will now be applied around Kaipara.

Sally Gilbert, the Ministry's Chief Technical Officer, Health, said the application of sand, granules or pellets will take place in infested areas to limit the potentially serious public health risks linked with the introduction of mosquito-borne disease into this country.

``Applying control agents is necessary to attempt to eradicate this exotic pest,'' Ms Gilbert said.

``There has never been an outbreak of a mosquito-borne disease in New Zealand and we want to keep it that way.''

The southern saltmarsh mosquito is a potential carrier of the Ross River virus disease. Symptoms include pain and tenderness in muscles and joints, fever, chills, sweating, a headache and tiredness. A rash may also briefly appear on the torso and limbs.

Southern saltmarsh mosquito larvae were found in the Rodney District of Kaipara Harbour in February last year. Since then, the mosquitoes have been found in about 2700 hectares of habitat around the harbour. This is just over 10 percent of the harbour perimeter. Extensive public consultation work as well as ground and aerial mapping of the area have taken place in the lead-up to the full eradication programme.

Ms Gilbert said the Government approved the use of a full-scale eradication programme around Kaipara in June. This means a two-pronged attack with Bti , which is currently being used, and S-methoprene, which has not yet been used in Kaipara.

``We're targeting the life cycle of the southern saltmarsh mosquito over two summers to ensure we treat over two breeding seasons,'' she said.

``Sites around Kaipara have been treated until now with Bti ? and Bti will continue to be used as part of the eradication programme. But now that the S-methoprene we ordered in July has arrived, we can use both agents.''

Ms Gilbert said Bti and S-methoprene have had full health impact assessments and leave no long-term residue.

Because S-methoprene is a slow-release product, it is the most effective way of killing the southern saltmarsh mosquito. Both products are already being used in eradication programmes in the Hawke's Bay and Tairawhiti. The products have also been extensively used in control programmes in Australia, Africa, the United States and Germany.

Disruption to the public will be limited as most sites being treated are in remote areas. The mosquitoes' habitat includes saltmarsh and nearby farm land and farm drains affected by peak tide flooding or heavy rain. All affected landowners have been contacted, before applications from helicopters, quad bikes and people on foot start later this week.

The southern saltmarsh mosquito is a particularly aggressive daytime biting mosquito. The Ministry advises people to try to avoid being bitten by any mosquitoes. Mosquitoes are most active around dawn, late afternoon and just after dusk. Screening open doors and windows, using insect sprays or mosquito coils indoors and wearing long clothing and repellent when outdoors, can reduce the possibility of being bitten.

Public notices about spraying are being placed in local papers this week. People wanting updated information on the application programme and sites can call 0800 MOZZIE (0800 669943) from tomorrow.

NZ Biosecure, whose staff have been involved in the control and eradication of Ochlerotatus camptorhynchus in the Tairawhiti and Hawke's Bay regions, have been contracted to run the southern saltmarsh mosquito programme and have set up a base in the Kaipara area.

Background Information:

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 be in New Zealand regularly (eg tourists or travellers returning from Australian states where Ross River Virus is endemic). Ross River virus disease can only be transmitted by mosquitoes, 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 is not a spray and does not drift. Sand granules are coated in the active ingredient. S-methoprene is used against mosquitoes throughout the world. It has undergone a full health impact assessment in New Zealand. S-methoprene breaks down quickly in the environment and is believed to be environmentally safe for use in New Zealand. Studies of non-target species where it has been applied in the Hawke's Bay have shown no impact.

What is the southern saltmarsh mosquito life cycle? The mosquito life cycle has four stages: The EGGS are laid in water. Southern saltmarsh mosquitos lay their eggs above the surface of the water and the eggs do not hatch until there is a king tide or heavy rainfall to wet them. The LARVAE hatch out and swim in water. The larval stage is when the mosquito is easiest to detect and is vulnerable to eradication measures. The PUPAE is the resting stage between LARVAE and ADULT. The pupa is difficult to detect. The ADULT is the flying and egg-laying stage of the insect's life cycle.

When and where were the larvae 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.

Have exotic mosquitoes ever been found in this area before? No. The Kaipara Harbour has always been considered a possible breeding ground for the southern saltmarsh mosquito, but none have been found in previous surveys of 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, which is less than was initially estimated.

How much funding did the Government allocate to controlling and eradicating exotic mosquitoes earlier this year? The total funding is approximately $30-million nationwide over four years. The money will be used to continue the eradication programme for the exotic mosquito in Tairawhiti, Mahia and Porangahau as well as the Kaipara and Mangawhai areas. The eradication programme in Napier has concluded, with no sign of southern saltmarsh mosquitoes for over two years.

The money was allocated in June this year and S-methoprene was ordered immediately from the USA. Its arrival this week allows treatment to start before the warm breeding season begins.

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