In July 2009, MAF Biosecurity New Zealand officials announced a significant milestone in their efforts to eradicate the southern saltmarsh mosquito (Ochlerotatus camptorhyncus) from New Zealand. They are to cease aerial spraying in the Wairua area in Marlborough as no larvae have been sighted in the area for over a year and no adults trapped for more than 2.5 years.
Wairau was the last New Zealand location under treatment since eradication activities began in 1998 with the discovery of the mosquito in Napier and then other subsequent locations. In 2009 elimination was declared in 10 areas including Napier, Coromandel, Kaipara and Grassmere (also in Marlborough). In 2010 it was anounced that this mosquito had been eradicated for all of New Zealand after normal ground-based surveillance activities of trapping and checking for larvae all came back negative.
A key eradication tool was the helicopter spraying of S-methoprene granules, an insect growth regulator designed to stop the mosquito pupae hatching into adults. In Wairau over a 4 years period, every 3 weeks an aerial application of S-methoprene was applied to areas of suitable habitat. This ranged from 150 hectares in the dry summer period to over 1,600 hectares in the winter. Spraying with Bti (Bacillus thuringiensis israelensis) is another tool used if live larvae are found.
The southern saltmarsh mosquito arrived from Australia
The southern saltmarsh mosquito is an unwanted immigrant from Australia. People first complained about the aggressive day-time biter (most of our native species prefer the shadier evening hours) in 1998 when it was discovered near Napier. In 2004, the mosquito was discovered in the Wairau estuary near Blenheim when duck hunters complained about aggressive mosquitoes on the lagoons. Wairau, in Marlborough, was the last New Zealand location under treatment.
Ross River virus is carried by these mosquitoes
The mosquito was a concerning arrival to our country as it is a known carrier of Ross River virus. This virus causes a debilitating flu-like disease in humans where the symptoms can persist for years. There is no vaccine to prevent this disease. Thankfully, there have been no cases of Ross River virus in New Zealand linked to these mosquitoes. In addition, the mosquito doesn’t just pester humans; it’s also a biting nuisance for livestock and birds.
What do I do if I think I have found a southern saltmarsh mosquito?
The southern saltmarsh mosquito can look very similar to other mosquitoes to the untrained eye. They are, however, an aggressive day-time biter and, as the name suggests, salt marshes are its preferred habitat. If you think you have found one, please take note of its location and phone the MAF Exotic Pest and Disease Emergency Hotline on 0800 80 99 66 to report the possible finding.