On track for eradication
Hand application of Bti following a
larval find. Photo: Flybusters.
Update: Southern saltmarsh mosquito eradication programme
A programme to eradicate the southern saltmarsh mosquito (Aedes camptorhynchus; SSM) from New Zealand has been in place since 1999 when it was first discovered in Napier. Since that time, the mosquito has been identified at 12 separate sites in New Zealand and the programme has successfully eliminated the mosquito from all but three of these places. The programme is on track to declare elimination of the mosquito from all known sites in New Zealand by 2010.
SSM is a vicious day-time biter and can transmit the debilitating human disease, Ross River Virus. In the absence of government intervention, this disease is predicted to have significant public health impacts.
If the final regional elimination is completed as planned in 2010, it is estimated that the programme will have cost around $70 million over an 11-year period.
In Biosecurity issue 72 (December 2006) 
(2102 KB) it was noted that the programme had been transferred from the Ministry of Health to MAF as part of the wider government decision to put all biosecurity management under the control of MAF Biosecurity New Zealand (MAFBNZ).
In mid 2007, the delivery of the eradication programme was tendered out and the contract let to Flybusters, an Auckland-based insect control company. Staff engaged on the programme operate out of three bases in the eradication zones at Kaipara, Coromandel and Blenheim, and at a laboratory in Auckland for the identification of specimens collected during field surveillance.
Eradication programme components
Science support
A technical advisory group provides independent technical advice to MAF, which is supported by a science programme. Currently a number of science projects are underway looking at egg survival and adult trapping efficiency in particular.
Surveillance and monitoring
Surveillance and monitoring of suitable habitat within the identified eradication zones is carried out to detect the presence of SSM larvae or adults. This is achieved by trained personnel walking the habitat (such as drainage ditches and saltmarshes) and dipping with ladles to extract any mosquito larvae found. In addition, each zone has an array of traps for adult mosquitoes. Capture of an adult potentially indicates either a treatment failure or a cryptic site that has yet to be located.
Treatment
Identified habitat within the eradication zones is treated with an insecticide-coated sand granule (s-methoprene) which is applied by helicopter at 21-day intervals. This is backed up by hand dosing of any ditches which the helicopter cannot reach. The methoprene does not directly kill the mosquito larvae, but prevents them from developing to adults and reproducing.
Eradication zones
Kaipara
In the southern Kaipara eradication zone, no larvae or adults have been located since July 2006, despite intensive surveillance since then. Methoprene treatment has also been ongoing since those finds. Subject to there being no further finds in this area, declaration of local elimination of SSM is on track for August 2008. This will be a significant achievement because, at the height of the infestation, SSM covered a very large area in the Kaipara.
Coromandel
In Coromandel, a similar situation exists; there have been no finds since April 2007.
In this area, in addition to the application of methoprene, other methods of eliminating SSM have been tried. In the area where the last finds were made, MAFBNZ and Environment Waikato have fenced off the salt marsh area to prevent stock access. This prevents the pugging effect which leaves hoof prints in the mud and allows SSM larvae to develop. There are also ecological
benefits from preventing stock access to these sites.
Blenheim
There continues to be isolated finds of SSM larvae in a confined area of the Blenheim eradication zone. The most recent find was in December 2007. While the numbers of SSM found continues to fall, it is clear that there are still unhatched egg banks in the area. It is thus vital that intensive surveillance continues and that treatments are accurately applied to all SSM habitat. In keeping with the ‘eradication rules’ set by the technical advisory group, it will be at least another two years before elimination of SSM from the Blenheim area can be confirmed, assuming no further finds. In the meantime, surveillance and trapping in the area around the more recent finds have been intensified. All these areas have also been treated with Bacillus thuringiensis israelensis (Bti) insecticide, which kills any mosquito larvae present.
In order to determine if there are further incursions (or further spread within New Zealand) of SSM, the Ministry of Health operates a national surveillance programme seeking the early detection of any SSM or other exotic salt marsh mosquito species outside the identified eradication zones. The surveillance provides vital support to the SSM eradication programme and will help determine when national eradication can be declared.
While there is still a long way to go and a lot of work to be done, all staff associated with the project remain confident that SSM can be eradicated from New Zealand.
- Flybusters/Antiants Insect Control (NZ) Ltd, PO Box 100-287, NSMC, Auckland, phone 09 440 9994, fax 09 489 7091
- www.flybusters.co.nz
For further information about the southern salt marsh mosquito programme:
- David Yard, Incursion Manager, Post Border, MAF Biosecurity New Zealand, david.yard@maf.govt.nz
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Page last updated: 18 June 2008