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Saltmarsh Mosquito eradicated from Mahia

Saltmarsh Mosquito eradicated from Mahia -- another year for Hawkes Bay and Gisborne

Health authorities have won a second battle against the Southern Saltmarsh Mosquito but warn that the war against the Aussie invader is still far from over, Associate Biosecurity Minister Marian Hobbs said today.

No adults or larvae of the saltmarsh mosquito have been detected in the Mahia Peninsula for two years and the mosquito is now officially regarded as eradicated from the area. The mosquito has also been cleared successfully from Napier where the Australian pest was first detected in 1988.

However eradication continues in nearby Porongahau, the last remaining Hawkes Bay site where the mosquito has been detected. It is on target to be cleared in August next year. Tairawhiti is expected to be cleared a month after that.

Meanwhile the largest eradication programme in the country is continuing in the Kaipara region, targeting a potential habitat of 2700 hectares.

The southern saltmarsh mosquito can carry the Ross River Virus with a wide range of debilitating symptoms lasting for up to a month or, in some cases, much longer.

There has never been a case of the disease contracted in New Zealand and Marian Hobbs said health and biosecurity authorities want to keep it that way.

Treatment with an insect growth regulator S-methoprene and a biological control agent, Bti, is conducted over the mosquito-breeding season in summer.

"I'd like to thank everyone involved for their input. The support for this programme has been really pleasing, with the community well behind the project," Marian Hobbs said.

The southern saltmarsh mosquito is a particularly aggressive daytime biting mosquito. 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.

Questions and Answers:

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 (e.g. tourists or travellers returning from Australian states where Ross River Virus is endemic). The Ross River Virus can only be transmitted by mosquitoes; it cannot spread from person to person.

What is the southern saltmarsh mosquito life cycle? The mosquito life cycle has four stages: The EGGS are laid in water. Southern saltmarsh mosquitoes 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 larvae stage is when the mosquito is easiest to detect and is most 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, biting and egg-laying stage of the mosquito's life cycle.

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 phase of the programme in Napier has concluded, with no sign of southern saltmarsh mosquitoes for over two years.

What chemicals are being used, and are they safe? S-methoprene is a slow-release 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. It may also be used in pelletised form. S-methoprene is used against mosquitoes throughout the world. Bti is also being used in eradication programmes in Kaipara, Hawke’s Bay and Tairawhiti, and has also been extensively used in control programmes in Australia, Africa, the United States and Germany. Both chemicals have undergone a full health impact assessment in New Zealand. They break down quickly in the environment and are 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 would happen if the eradication programme didn't go ahead? If the southern saltmarsh mosquito got established in the North Island the chances of an outbreak of the Ross River virus would be greatly increased. If someone coming into the country with the virus in their system was bitten and the mosquito then bit another person, the virus would be spread to the second person. An estimate done in 2001 put the cost to the taxpayer of an outbreak in Auckland alone more than $38 million - and that estimate is thought to be conservative.

Where else are the eradication programmes being carried out?

Napier and Mahia: This programme has been completed. Surveillance is continuing as part of the public health service's routine monitoring of high-risk mosquito habitats.

Porangahau and Tairawhiti: Applications of mosquito control agents have been completed at all sites. The last mosquito found in Porangahau was in August 2002. If no further larvae or adults are detected, eradication will be completed in September 2004. The last mosquito detected in Tairawhiti was in September 2002. If no further adults or larvae were found, eradication would be completed in October 2004.

Kaipara: The Kaipara eradication programme is being fully implemented. Permanent sentinel surveillance sampling sites have been established at 31 locations including Mangawhai and Whitford, and sites are visited twice weekly and sampled for adults and larvae. Sites have been selected to represent known positive areas; intermittently positive areas and known negative sites and reports include community reports of unusual biting activity. Only single adults were found in each of August and September 2003 and no adults were found in October 2003. Whitford: After finding several adults and larvae in February 2002, an eradication programme was begun. There have been no sightings of mosquitoes for some months now, and if that continues it's expected the treatment phase will be able to finish around March 2004 and the area will go into surveillance phase.

Mangawhai: After the initial discovery at Mangawhai, north of Kaipara in about April 2001, no further larvae or adult salt marsh mosquitoes were found at that site for some 15 months. Then following a large water event a single adult was captured. Surveillance was stepped up and is ongoing with no further finds of mosquitoes to date.


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