Mosquito Response Programme: Health Information No. 1

Mosquito Response Programme: Health Information No. 1

HE Code: 
Leaflet A4 (online only)
Publication date: 
1 May 2003
Status: This resource is online only.
Web-only information about spraying to eradicate the Southern Saltmarsh mosquito, Ochlerotatus camptorhynchus, for use in affected areas.

An eradication operation is underway to get rid of the southern saltmarsh mosquito Ochlerotatus camptorhynchus. This mosquito has been introduced to New Zealand from Australia. It can carry the Ross River virus which can cause disease in humans.

Ross River Virus Disease

Ross River virus disease can cause a wide range of symptoms, the most frequent of which is inflammation of the joints. The disease has been reported from all the states of Australia, as well as from Papua New Guinea, the Solomon Islands and some other Pacific islands.

All cases reported so far in New Zealand have been in people who have travelled from overseas. It has not yet been found in mosquitoes here.

People infected by the Ross River virus may have pain in muscles and joints, and other symptoms including fever, chills, sweating, a headache and tiredness. There may also be a rash on the body and limbs for a short time. The symptoms can only be confirmed by a special blood test.

There is no cure for Ross River virus disease. The symptoms occur mainly in adults, and occur 3-21 days (average 9 days) after being bitten. The symptoms can be relieved by painkillers and usually fade away within weeks. In a few cases they may persist for months or years. Infected children are much less likely to have symptoms.

The only way people can be infected with Ross River virus is through being bitten by a mosquito which is carrying the virus. The virus cannot be spread from person to person.

Avoid being bitten

Most mosquitoes are active at dawn, around late afternoon and just after dusk. However, the southern saltmarsh mosquito is more active in the morning and during the day. The risk of being infected with Ross River virus is low, but to avoid the nuisance of bites which can be uncomfortable:

At home

  • put screens on windows and doors
  • use insecticides and repellents eg, mosquito coils and aerosols
  • use bed nets
  • use insect sprays indoors when mosquitoes are around.


  • wear a repellent cream or spray
  • wear protective clothing (loose fitting long-sleeved shirts and trousers)
  • use an insect screen on tents
  • avoid places where mossies are most active, such as swampy areas
  • carry a can of insect repellant in your vehicle.

If insect repellents are a concern use non-allergenic products.

Bti – is it safe?

Bti is effective against mosquitoes and blackflies (sandflies).

Wide research shows Bti is extremely safe and organic. It will not affect aquatic plants, organisms or fish, and it has undergone a full health impact assessment which shows that it poses no risk to mammals, including humans.

It does not stay long in the environment after it is applied but breaks down within days. It leaves no residue.

Bti has been used extensively in mosquito and biting fly control programmes, especially in Africa, the United States, Germany and Australia. Over 40 tons of Bti have been applied in West Africa alone with no reported effects on the environment.

Applying Bti

Application programmes will be by helicopter, vehicle-mounted equipment or handtreating of affected areas. Applications are only carried out over saltmarsh areas after mosquito larvae have been found.

No special care needs to be taken by the public during the eradication programme. However people with severe or unstable asthma or other respiratory conditions, immune conditions, allergies, or others who have concerns such as pregnant women, can reduce exposure to the Bti by avoiding the treated sites.

Continue to take your prescribed medication.

What about Bti lying on the ground or in the water?

No health problems are anticipated from residue as it breaks down naturally.

What about spray on fruit and vegetables?

Domestic gardens are not treated as part of this programme. No health problems are known to arise from eating fruit and vegetables treated with Bti. Wash all fruit and vegetables in the normal way.

What about water?

Bti is extremely unlikely to enter the drinking water supply. However, contact with treated water is not anticipated to cause any health problems.


Further information about the eradication programme can be found on the Ministry of Health’s Website – – under News and Issues.

Contact your doctor or other health advisor in the usual way if you have any health worries.