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Southern Saltmarsh Mosquito In Kaipara Harbour

Confirmed Finding Of Southern Saltmarsh Mosquito In Kaipara Harbour

Mosquito larvae found in the Rodney District of the Kaipara Harbour during routine surveillance last week, have been confirmed as being the exotic southern saltmarsh mosquito, Aedes camptorhynchus.

Seven larvae samples, suspected as being Aedes camptorhynchus, the southern saltmarsh mosquito, were detected during routine surveillance last week, and sent to Australia for official identification. Aedes camptorhynchus is an unwanted organism in New Zealand.

Dr Bob Boyd, chief technical officer for biosecurity in the Ministry of Health, said that while the finding showed that the national surveillance programme was working, it was extremely disappointing to find this unwanted mosquito at another site, well away from previous finds.

Surveillance programmes have been in place since December 1998 when the exotic mosquito was first found in Napier, Hawke's Bay.

"An eradication programme in Napier has been progressing well, as have the containment programmes underway at Muriwai in Gisborne, and Porongahau and Mahia in Hawke's Bay.

"There have been no adult mosquitoes or mosquito larvae found in Napier for many months. However, before we can confidently say that the area is free of the exotic mosquito, the programme has to continue for another two years.

"In Muriwai, Mahia and Porongahau, there is ongoing containment of the southern saltmarsh mosquito within the known habitats, and no new positive habitat has been identified since December 2000. Currently, there are 24 hectares at Porangahau, 63 ha at Mahia and 86 ha in the Gisborne area being treated with s-methoprene to contain the mosquito.

Dr Boyd said that the Ministry and the local public health service immediately put in place an intensive survey covering more than 150 hectares to determine the potential habitat and location of colonies in the Kaipara area.

A progress report on that survey will be presented to an expert Technical Advisory Group early next week. The Ministry will use the advice from the Technical Advisory Group, as it considers the possible long term response to the southern saltmarsh mosquito in New Zealand.


For more information contact: Selina Gentry, Media Advisor, ph: 04-496-2483 or 025-277-5411 Internet address:

Questions and Answers

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 Tuesday 20 February the Ministry of Health was alerted that 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.

Why were the samples taken nine days after the water event? The surveillance work had actually started five days after the water event, but it was on the fourth day of surveying that these samples were collected. We know that the southern saltmarsh larvae relies on saline water for its survival. Heavy rainfall and/or high tides after a period of dry weather is known to activate larvae laid earlier in the year. Larvae can survive up to nine months. The period of five to nine days allows eggs to hatch into larvae so they can be found. These specimens collected were 'late fourth stage instars', which means they were most likely to have been larvae from eggs which hatched after being inundated during the high tide and heavy rainfall.

Is there any suggestion as to how the southern saltmarsh got to Kaipara Harbour? We do not know when or how they arrived in the area. We do know that the southern saltmarsh species does prefer coastal areas due to a preference for saline water habitats, and it is believed that the species has a 5 kilometre flight range. We will be seeking the technical advisory group's advice on this question.

How widespread is the mosquito in the Kaipara Harbour area? It is not possible at this time to say how widespread it may be, or how it arrived or when it established here. However, this area has been surveyed for some time, with enhanced surveillance being undertaken following the finding of southern saltmarsh mosquitoes in the Gisborne area in October 2000. No evidence of establishment has been detected until now.

What happens now? An intensive survey of the area is underway to confirm the extent of breeding sites, and identification of other potential breeding areas. This study will be completed next week. A progress report will be reported to the technical advisory group which will meet early next week.

What advice is being given to people in Kaipara Harbour area? The public have an important role in the containment programme. They are asked, if possible, to take any mosquito specimens to their Public Health Service, and also report any incidents where they suspect the presence of southern saltmarsh mosquito. The southern saltmarsh mosquito is known to be an "aggressive day-time biter", whereas the endemic mosquito is more commonly active during the evening.

Can we be sure the mosquito hasn't spread further afield? No. However, we do have a national surveillance programme in place whereby sampling of potential habitat is occurring after heavy rainfall. This programme ensured early discovery of the unwanted organism in the Kaipara Harbour area, Gisborne, Mahia and Porongahau sites. Containment programmes have been implemented in Gisborne, Mahia and Porongahau, and appear to be showing signs of success. The mosquito has not been found in any new habitat since December 2000.

In the Napier case, an eradication programme has been in place since December 1998, and no adult mosquitos or larvae have been found for many months.

Has a decision been made about the future management of the southern salt marsh mosquito in the Gisborne and Central Hawke's Bay regions? No. At this stage the containment programme will continue until a decision is made.

When will Government be making a decision on future management of the exotic mosquito? The Ministry of Health had been due to report to Government by 31 May 2001 on options for a long-term response to the southern saltmarsh mosquito. The implications of this new finding at Kaipara will be included in the Ministry's advice.

Have adult southern saltmarsh mosquitos been found recently at any of the other sites? No

What impact does this discovery in Kaipara Harbour have on the future of all programmes? The Ministry of Health had been due to report to Government by 31 May 2001 on options for a long-term response to the southern saltmarsh mosquito. The implications of this new finding at Kaipara will be included in the Ministry's advice.

How much money annually has been allocated for future management of the Southern Saltmarsh mosquito? None - The Ministry of Health is due to report to Government by 31 May 2001 on options for a long-term response to the southern saltmarsh mosquito. The implications of this new finding at Kaipara will be included in the Ministry's advice. At that time, the costs and benefits of each option will be described and the funding for the preferred option will be estimated.

What is s-methoprene S-methoprene is being used to supplement Bti, the control agent already being used. These two products are the same ones used already in the Napier eradication programme, both of which have undergone full health impact assessment. Bti, which is a biological spray, leaves no long-term residue and has no other impact on the environment or people. S-methoprene is an insect growth regulator that stops the mosquito pupae hatching into adults. It has been used extensively overseas to control mosquitoes.

S-methoprene breaks down quickly in the environment and is believed to be environmentally safe for use in New Zealand. Studies of the impact on non-target species where it has been applied in the Hawke's Bay have shown no impact.

Selina Gentry Media Liaison Communications Corporate & Information Directorate Ministry of Health DDI: 04 496 2483

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