What we do and why we do it – Mosquito Surveillance

 

There is real benefit to everyone you know through the early detection of exotic mosquitoes. If they can be found early, they can be gotten rid of more easily. It is a clear method of protecting yourself and your family, friends, workmates, domestic stock, and native wildlife from disease spread by exotic mosquitoes.

 

Mosquito Consulting Services NZ undertakes surveillance for the early detection of exotic mosquitoes.

 

We target a range of mosquitos known to be important for transmission of diseases such as Ross River virus and Barmah Forest virus. Generally, disease spreading mosquitoes also are a significant nuisance to humans and livestock from painful biting attack as they require a blood meal for each batch of eggs the female will ever produce. We are looking mostly for exotic mosquito species as the mosquitoes native to New Zealand, or ones previously introduced and now endemic, are not responsible for disease transmission. Examples of the mosquitoes we are looking for include Australian salt-marsh mosquitoes (Southern Salt-marsh Mosquito: Aedes camptorhynchus and its northern cousin: Aedes vigilax) and freshwater breeding species including Culex annulirostris. All of these mosquitoes are efficient at transmitting a number of viruses capable of causing human disease and some disease in domestic and native animals. Mosquitoes don’t transmit all viruses. They don’t transmit cold or flu viruses. They don’t transmit the aids virus or hepatitis. They only transmit viruses that can infect both mosquitoes and people simultaneously (and selected domestic and native animals). There are also non-viral diseases transmitted by mosquitoes such as Malaria. Malaria is however considered a small risk here.

 

Mosquito surveillance needs to go to where the mosquitoes are. We cover a lot of ground around the types of habitats each exotic species needs for breeding. All mosquitoes need water in which to complete their breeding cycle. Depending on the mosquito species involved, some need salty ground pools in salt-marsh, tidal drains, pasture and reclaimed land that still contain high salt levels. A high tide that covers salt-marsh then leaves salt-water filled depressions is ideal. Reclaimed pasture that no longer gets flooded by tide but does still get saturated by rain is still suitable habitat for salt-marsh mosquitoes. Salt-marsh mosquitoes will tolerate a very wide range of salinity. From concentrated sea-water (as pools dry they get saltier) to relatively fresh water after high rainfall has flushed out much of the salt.  Fresh water breeding mosquito species can use a very wide range of breeding opportunities.

The high risk mosquito, Culex annulirostris breeds in grassy ground pools following rain. Semi-flooded pasture is ideal. Other species that include the carriers of the viruses that cause Dengue breed in small container type situations including discarded auto tyres, drums, pots, plastic sheeting, anything that holds water after rain.

 

When we are looking for exotic mosquitoes, we search for the mosquito larvae while they are still developing in their breeding site. We also set special traps that attract the adult mosquitoes from a wider area. We sample for mosquito larvae by walking through the breeding habitat and taking dips of water using a ladle on a long handle and looking carefully for mosquito wrigglers. This can be tricky as newly hatched mosquito larvae are very small, almost transparent and hard to see. We sometimes take a few minutes to look at each dipper of water. Older larvae are larger and much more easily seen. We take samples of mosquito larvae, kill them in ethanol and dispatch them to the Mosquito Consulting Services NZ laboratory in Lower Hutt. Our entomologists than make positive species identification by confirming key microscopic features presence or absence against published formal descriptions of the species.

The mosquito larvae are only present in the breeding site when it is wet and semi-flooded. We make all of our sampling visitations during suitable weather conditions that improve the likelihood of finding mosquito larvae. Adult traps are used anytime as the adult mosquitoes may disperse over long distances and be around for some time after breeding sites have dried up.

 

How long does a mosquito live for? It depends greatly on weather conditions. During hot dry weather, adult mosquitoes may live for only a few days before they dry out and die. In cooler, wet conditions mosquitoes may live for several weeks.

 

We work closely with land owners and managers to ensure that we don’t cause a bother during busy periods on farms. MCSNZ staff use duel-cab utes for land transport and often tow a quad-bike to use to move efficiently across properties. We take a lot of care to not damage pastures and when it’s too wet, we generally walk the final leg to get to the sample points we need. We take nothing but the mosquito samples. We like to keep in contact with land owners and managers to let them know what we are doing and what results we are seeing. Mosquitoes bite people and some of the best surveillance we get is from land owners and managers that are on site all of the time and saying if they are being bitten or if they have noticed any problems with stock. So there is real benefit in keeping good communications with land owners and managers as it is in everyone’s self-interest to detect exotic mosquitoes early and protect yourself and your family, friends, workmates, stock, and native wildlife from disease spread by exotic mosquitoes.