Culex sitiens

In March 2018, we found larvae from an exotic mosquito species, Culex sitiens, near the Kaipara Harbour, north of Auckland. Find out about the mosquito and what we're doing about it.


26 October 2018 – Aerial spraying programme

In late October and November 2018, Biosecurity New Zealand will be doing aerial spraying to try to eradicate Culex sitiens from the area near the Kawau Parua Inlet.


A closeup of a Culex sitiens mosquito on a human hand
Culex sitiens mosquito

Culex sitiens is wide-spread in Southeast Asia, the South Pacific, and Australia.

It is known to transmit diseases such as Ross River virus. However, this is not a risk for New Zealand as this disease is not present here. Culex sitiens may also be able to transmit Japanese encephalitis but this has not been observed outside of a laboratory.


How was it found?

Culex sitiens larvae were found near the Kaipara Harbour in the Kawau Parua Inlet (north of Auckland). The larvae were found during regular surveillance as part of Biosecurity New Zealand’s National Saltmarsh Mosquito Surveillance Programme. Up to 29 October 2018, no adult mosquitoes have been found.

What's being done?

Contractors for Biosecurity New Zealand have taken water samples and set light traps to collect larvae and trap adult mosquitoes in and around the area where the larvae were initially found.

Only a small number of larvae have been found and no adults have been detected. Surveillance of the surrounding area has determined it has not spread from the site where they were originally detected.


We have a good chance to successfully eradicate the Culex sitiens mosquito from New Zealand.

In late October and November 2018, Biosecurity New Zealand will be doing an aerial spraying programme to attempt to eradicate the Culex sitiens from the area near the Kawau Parua Inlet.

Biosecurity New Zealand has successfully eradicated exotic mosquitoes in the past, including in this area.

What is the spray?

The treatment used is called Vectobacc. It contains the active ingredient Bti (Bacillus thuringiensis subspecies israelensis).

Bti is a biological and naturally occurring bacterium found in soils. It contains spores that produce toxins, which only kill larvae, or mosquitoes when they are in the water.

Bti is not toxic to humans or animals. It's approved in the United States for pest control in organic farming operations.

Spray area

The treatment will be applied to wet areas in the Kawau Parua Inlet. This includes a 5km radius around the sites where larvae have been found. Most of the area is pasture and other non-habitat areas so treatment will only be applied to part of this area.

A helicopter will be used to spray the treatment on a day after 29 October 2018, when the weather permits. We are planning to do 4 applications, with a week between each treatment, covering the same radius each time.

There is always a chance that the use of a low flying helicopter could spook animals. If you have horses and other animals in the vicinity and would like to discuss the spray programme and timings, contact Don Hammond, by emailing

Aerial treatment will be done first thing in the morning. This is when the weather is most predictable and there is usually less wind. However, we may apply the treatment at other times of the day if the conditions are right.

Find out more

Who to contact

If you see unusual mosquitoes call the Mosquito Hotline on 0800 MOZZIE (0800 66 99 43).

If you have health concerns after being bitten by a mosquito you can call the Ministry of Health's Healthline on 0800 61 11 16.

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