Mosquito Information for New Zealand

One of the most commonly asked questions about mosquitoes that we get is "How do I kill them?" The adults do the biting so most people think if they kill the adults they won't be bitten. This is true, but more adults are usually only a hatch away.
Mosquito control in and around your home can be achieved by getting rid of the habitat they like to live and breed in. Larvae are aquatic so they need water to survive. The adult female will usually lay her eggs on the surface of water (in an egg raft), or on the dirt or soil just above the waters edge.  If you get rid of the habitat where the larvae hatch from the eggs, then you'll have fewer adults around and less chance of being bitten. Mosquito prefer a warmer ambient temperature so they are at their highest numbers from spring through to late summer and warmer autumns.
 

What is Good Mosquito Breeding Habitat?

It would be nice if all mosquito species simply breed in nice clean fresh water. Unfortunately each species is different, some like salty water, some like fresh water, some like brackish, some like high organics in the water, some like it very clean. In your backyard there are usually two culprits - Culex pervigilans and Aedes notoscriptus. There are a few more species that we have in New Zealand that do bite humans, but generally if you control the habitat on your property with these two species in mind, then the others are unlikely to be a problem.

Culex pervigilans is the most common domestic pest mosquito in New Zealand and is found throughout the country. Its primary host is birds but it will happily bite larger mammals including humans and cattle. This species is able to breed in a wide variety of habitats, almost anywhere where water is collecting, which is why it is so wide spread. Larvae have been found in fresh, brackish, and polluted water, in temporary and permanent ground pools, natural and artificial containers and slow moving streams. They thrive in both urban and rural environments and will breed in troughs, tanks, vases, toilet cisterns, gutters, jars, tins, pot plant drip trays, bottles, tyres, buckets and almost any other type of container left lying around to collect water. It lays its eggs on the surface of the water in rafts. It can lay up to 300 eggs in as little as 15 minutes! Culex pervigilans is a noctural or night time biter. It doesn't have very distinctive markings.
More.
Aedes notoscriptus is an introduced species, but it has been in New Zealand since at least the 1920's when first discovered. It is very common in the North Island, but is also found as far south as Canterbury and it's range appears to be on the increase. It is a fresh water container breeding mosquito, preferring vegetated containers in well shaded areas, found in tree holes and fresh water rock pools. It has also adapted to artificial containers including pot plant drip trays, gutters, jars, tins and other similar items. It is very common around back yards particularly where bush and vegetation is present. The female lays her eggs at the water level around the edges of containers, they are laid as individual eggs. Aedes notoscriptus is a day and night time biter, coming out of the shade during the day to bite is very common. This mosquito is readily recognised by its distinctive markings, being black and white with white stripes on the legs and proboscis. More.

How to Get Rid of Mosquito Habitat?

If you can eliminate the mosquitoes habitat you'll stop them from breeding. These are simple things to do in your backyard to get rid of mosquito habitat:

• Checks gutters and drains are clear of leaves and other debris regularly - this stops water from pooling.
• Make sure rain water collecting tanks are covered and sealed.
• Keep swimming pools well chlorinated and free of dead leaves.
• Empty and clean pot plant drip trays and fill with sand (sand stores the water for the plants but its not suitable for the mosquito).
• Overturn any outdoor item that can't be removed so that water doesn't sit inside it - eg boats, dingy's, drums, unused sandpits and paddling pools etc.
• Cover venting pipes or small gaps on septic tanks.
• Fill or drain holes in the ground that store water.Emp
• Empty and clean pet drinking water vessels regularly.
• Fish ponds - try to find fish species that love mosquito larvae. Over summer there may be too many larvae for the fish to eat, this is one area where mosquito dunks are a good idea.
• Old tyres - mosquitoes love tyres! make sure they have a drain hole in them or get rid of them completely.
• Make sure you remove any rubbish such as old cans, tins, jars, bottles or any other items including plastic that can hold water.
• Under the trees - try to provide a heavy mulch to prevent water from pooling, weed mat compresses the soil and often results in pooling under the weed mat that those clever mosquitoes can still get at.
• The Ministry of Health produced this pamplet a few years ago, but it contains the best simplest methods to help control mosquitoes in and around you home.

 

What is the Best Product to Use to Kill Mosquitoes?

After years of putting up with mosquitoes New Zealand now has access to some simple and safe products suitable for the backyard control of mosquitoes. It has taken awhile, but everyone in the community can now access Bti - Bacillus thuringiensis israelensis. Bti is a group of bacteria used for the biological control of mosquito larvae. Bti produces a toxin in the gut of the mosquito larvae, which destroys the larvae gut lining causing death, usually within 12 hours. 4th Instar larvae (the large larvae) and pupae are non-feeding and thus won't be affected by Bti, so its good to use it regularly while the larvae are still young. Mosquito dunks and Bti granules provide a residual from 1 to 4 weeks which means you only need to treat water with them once a month. Bti powders and liquids need to be mixed with water, and don't usually last longer than 48 hours. They are great for a quick knock down but you'll need to apply every couple of days.

One of the hardest areas to treat and control is under vegetation. Bti granules can be used here, sprinkle in and under the dripline of trees and the granules will fall where rainwater falls, providing treatment in areas that are hard to see but where mosquitoes will happily breed.  More.
Bti is quite specific for mosquitoes and other insects species are not affected, although it can also be used for fungus gnat control. More.

Another great control product very new to the world market and available in New Zealand is Aquatain. This is a silicone based liquid that only needs a few drops per square meter to make the surface of the water unsuitable for the mosquito larvae to breath and they die of suffocation. Mosquito larvae feed with a 'siphon' which pierces the surface of the water, the Aquatain affects the surface tension of the water and the larvae siphon can't pierce the surface to reach air. Perfect!
Aquatain stays across the surface of water so even when the water surface is affected by wind Aquatain doesn't shift with the wind like some other liquid control products. It also has a great residual providing control for up to one month. After a month it tends to be broken down by UV action of the sun.  More.
 

So Bti and Aquatain will kill the larvae, what about the adults?

There are numerous chemical insecticides that can be applied inside and outside for the control of mosquito adults. Unfortunately most of them are not specific to mosquitoes and can kills other flying insects including bees.
For most people a can of fly spray (read the labels, the best ones are those that claim to have a residual) in and around trees will kill most adults that land on the vegetation. Simply spray the can amongst the vegetation where you know the mosquitoes are living making sure you spray from the bottom up to get contact with the underside of the leaves (mosquitoes hide under the leaves). You can spray as often as you like, sometimes a few hours before you are going to be outside enjoying a BBQ dinner is all thats required to keep the numbers low for the evening and a few days afterward.
You can also contact professional pest control services who can apply commercial chemical insecticides.

Some mosquitoes seem to like clothes on washing lines that are under eaves and shaded. Ensuring you shake your washing before removing from the line will help to avoid the adult mosquitoes getting a free trip inside your house. Once inside they often hide until night time when they'll come out of hiding for a blood feed - usually off of you!

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