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Two suspicious mosquito larvae found

Media Release

March 6, 2002

Two suspicious mosquito larvae found south-east of Auckland

Intensive surveillance is planned around the coastline in the Auckland region following the discovery of two suspected southern saltmarsh mosquito larvae in a creek near Whitford, says the Ministry of Health.

The Ministry was concerned as the southern saltmarsh mosquito Ochlerotatus camptorhynchus could spread Ross River virus disease, said Dr Bob Boyd, chief technical officer for biosecurity.

There has never been a case of New Zealand-acquired mosquito-borne disease in this country.

Dr Boyd said photographs of the larvae have been sent to Australia for confirmation.

"If they are confirmed as southern saltmarsh mosquito larvae it will be very disappointing but this is the reason we have kept monitoring the areas where the mosquito could be found."

The larvae were found at one site on Monday near the eastern mouth of Turanga Creek during routine checks of likely mosquito habitat following last weekend's king tide. This is the first time exotic mosquitos have been identified in this area.

An intensive survey of the coastal region from Howick to Miranda and east to Waiheke Island will be carried out tomorrow and Friday to check for any other signs of the mosquito. A team of experts will fly by helicopter to a number of sampling sites.

"It's essential this survey is completed within the next 48 hours so any larvae that hatched during last weekend's king tide can be found before they transform into pupae."

No evidence has been found of the mosquito in the area between Whitford and the Kaipara Harbour. The mosquito's natural flight range is estimated at five kilometres.

The southern saltmarsh 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 increases the size of waves can all encourage hatching.

Southern saltmarsh mosquitos have been found in Kaipara, where a long-term programme is underway to contain the mosquito and reduce the adult biting population, and around the Napier and Gisborne areas.

"When outlying sites were found near Napier, we then carried out a broad and intensive survey to find out how far the mosquito had spread. Our treatment programme at these sites is proving successful and suggests that eradication will be achieved."

New Zealand BioSecure has sprayed more than 170 hectares of mosquito habitat from the ground and the air at 22 sites around the Kaipara Harbour.

Auckland Healthcare carried out previous surveys in Manukau and Mangawahi harbours between February 2001 and November 2001 and on those occasions no mosquitos were found.

Dr Boyd said the Ministry would appreciate residents in the Whitford area advising the local public health service if they see or are bitten by any suspicious mosquitos. The southern saltmarsh mosquito is an "aggressive" daytime biter.

He also advised people in the area to try to avoid being bitten by any mosquitos. Mosquitos are most active around dawn, late afternoon and just after dusk. By screening open doors and windows, using insect sprays or mosquito coils indoors, wearing long clothing and repellent when outdoors, the possibility of being bitten can be reduced.

For more information contact: Anne-Marie Robinson, Media Advisor, ph: 04-496-2067 or 025-802 622 http://www.moh.govt.nz/media.html


Why is it important the initial survey is completed within 48 hours before any larvae that may have hatched following the recent king tide become pupae? The mosquito life cycle has four stages, these being 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 stage of the insects life cycle. Breeding and egg laying occur. An adult female southern saltmarsh mosquito requires a blood meal before laying eggs.

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 mosquitos 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. We now know the potential habitat is about 2710 hectares.

What spray is being used 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 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.

How much funding did the Government allocate to controlling and eradicating exotic mosquitos in 2001? There has been $5-million has been 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, as phase one of a possible eradication programme.

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