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Spraying To Control Exotic Mosquito - Kaipara

Spraying To Control Exotic Mosquito Starts In Kaipara

Spraying to control the southern saltmarsh mosquito Ochlerotatus camptorhynchus will start this week on private properties in Kaipara Harbour, the Ministry of Health announced today.

Treatment is taking place in infested areas to limit the potentially serious public health risks linked with the introduction of mosquito-borne disease into this country, said Dr Bob Boyd, Chief Technical Officer, Health.

"Applying control agents is necessary to attempt to stop the spread of this exotic pest. There has never been an outbreak of a mosquito-borne disease in New Zealand and we want to keep it that way."

The mosquito is a potential vector for Ross River virus disease.

The decision to start spraying this week was made after advanced larvae specimens and adults were found at several sites around Kaipara Harbour.

Sites will be treated with the biological spray Bti -- already being used in eradication programmes in the Hawke's Bay and Tairawhiti. This product has also been extensively used 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.

Disruption to the public will be limited as most sites being sprayed are on private property in remote areas. All affected landowners will be contacted before spraying from quad bikes and knapsack sprayers starts this week. Aerial applications of spray will be used to treat less accessible areas away from residential properties.

Southern saltmarsh mosquitos were first identified in the Kaipara Harbour area in February this year. Since then, extensive public consultation work as well as ground and aerial mapping of the area have taken place.

Spraying is the first step in containing the mosquito in areas where its presence is known.

Containing the mosquito will also help reduce the adult biting population below the level where it could expand further and create a threat to public health ahead of decisions on a long-term eradication or control option, Dr Boyd said. Ongoing surveys of mosquito habitat in and around the Kaipara Harbour will continue to take place.

At this stage no further larvae or adult salt marsh mosquitoes have been found at Mangawhai since earlier this year. Spraying will not be carried out unless larvae are found. Any treatments at Mangawhai will be carried out by ground.

The southern saltmarsh mosquito is a particularly aggressive daytime biting mosquito. The Ministry's advice is that people should avoid being bitten by any mosquitoes. Mosquitoes are most active around dawn, late afternoon and just after dusk. The possibility of being bitten can be reduced by screening open doors and windows, using insect sprays or mosquito coils indoors and wearing long clothing and repellent when outdoors.

Public notices about spraying are being placed in local papers this week and a maildrop is planned. People wanting updated information on the application programme and sites can call 0800 MOZZIE (0800 669943). The Ministry's website will provide regular updates under 'News' link.

NZ Biosecure, whose staff have been involved in the control and eradication of Ochlerotatus camptorhynchus in the East Coast 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.

Meanwhile, Australian taxonomy experts have identified the exotic mosquito larvae found at the Port of Auckland on December 1 as Ochlerotatus japonicus (formerly known as Aedes japonicus).

Ministry of Agriculture and Forestry quarantine staff were inspecting used vehicles and machinery on board the vessel MV Capricorn Ace that had sailed from Japan when they found the mystery mosquito larvae.

New Zealand taxonomy experts advised the exotic mosquito was an Ochlerotatus mosquito but the exact species could not be determined. Further examination and comment was sought from an Australian expert and now a conclusive identification has been made.

Dr Boyd said Ochlerotatus japonicus can carry the Japanese encephalitis virus which can cause fever and encephalitis and may result in death for some patients.

Since the larvae was found, mosquito traps at Auckland and Wellington ports were being checked regularly as an extra precaution. No further mosquitoes or larvae have been found.

Exotic mosquitoes that have public health significance have been intercepted on twelve previous occasions since January 1998 - three of which have been identified as Ochlerotatus japonicus.


Background Information:

When and where were the larvae found in the Kaipara area? Sampling was taken in the Kaipara Harbour area on 18 February, 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 mosquitos have also been found in the area.

Have exotic mosquitos 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. We now know 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 mosquitos earlier this year? The total funding is $6-million nationwide over four years. Of this, $5-million has been approved for spending over four years. The money will be used to eradicate the exotic mosquito in Napier, Gisborne, Mahia and Porongahau and to contain and control the spread of the mosquito in the Kaipara and Mangawhai areas, with eradication remaining an option. An additional 0.25-million per year has been approved for the Ministry of Health's enhanced capacity for biosecurity work. It will also enable enhanced disease response measures in Auckland and Northland.

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