Mosquito

Scientific Name: Family Culicidae

How to identify a mosquito

Adult mosquitoes both have a long proboscis which the males use to feed on nectar. The female, however, feeds on blood which leads to the transmission of disease.

Where are mosquitoes commonly found?

Mosquitoes can be found in a variety of environments but are often found in areas with water sources. The mosquito can exploit a range of fresh and salt water sources – natural or artificial - for breeding habitats.

Why are mosquitoes considered a pest?

Mosquitoes are commonly known for leaving an itchy rash when they bite due to the transfer of mosquito saliva. In addition to being a nuisance, mosquitoes are also vectors for a range of dangerous diseases. In Australia, instances of mosquito related disease are mostly isolated to the northern tropical regions but various species can act as carriers for serious diseases such as malaria, dengue fever and filariasis and the Ross River virus in humans as well encephalitis in horses and heartworm in dogs. Mosquito-borne malaria is one of the world’s major infectious diseases, killing around two to three million people each year.

What is the biology and lifecycle of a mosquito?

Australia is host to over 300 species of ‘mozzies’ which start their lifecycle as aquatic larvae until the adults emerge as little as one week later, in optimum conditions. The mosquito can exploit a range of fresh and salt water sources – natural or artificial - for breeding habitats.

A few days after a blood meal, female mosquitoes lay about 200 eggs on any water surface-even small water bodies such as bottom trays of potplants are suitable. Most species produce egg 'rafts' where many eggs are cemented together, floating until they hatch after two to three days. Although they live in water, the larvae known as 'wrigglers' breathe air and come equipped with their own snorkelling equipment. Attached to their abdomen is a siphon, which they use when they come to the surface to breathe.

Chemicals Required to Control Mosquitoes

Chemical control involves the application of products designed to kill mosquitoes, either in the larval stage through physical damage or hormonal disruption, or in the adult stage through nervous system disruption.

The use of chemicals must form part of a larger integrated approach to mosquito management and should not be considered a stand-alone control strategy. Every effort should first be made to prevent mosquito breeding through physical control activities, such as habitat source reduction or breeding site maintenance, reducing the need for chemical application. Avoiding over-application of chemicals with the same mode of action will also help to prevent the development of chemical resistance.

Larvicides kill or disrupt the development of mosquito larvae, resulting in death before the adult can emerge and pose a potential health or nuisance risk. If used at specified label rates, larvicides are target-specific. Therefore, the environmental impact can be limited through appropriate product use. For these reasons, larvicides should be considered the preferred option over adulticides, if chemical control is deemed to be the most appropriate management strategy.

It is important to determine if the larvae collected are a species that is of concern as a nuisance or public health risk and therefore require chemical control.

The advantages of larvicide application include:

• target-specific when applied at the label rate, resulting in minimal impact on the environment

• require a potentially smaller area to treat as larvae are confined to breeding sites (compared to adulticide application)

• a range of product formulations are available allowing for flexibility in treatment

• no specialist equipment required when treating small areas.

The disadvantages of larvicide application include:

• breeding sites need to be mapped, which can be labour intensive

• different products are effective at different stages of mosquito lifecycle, leaving a small window of opportunity for larvicide application to be successful

• treating large areas can be impractical and expensive.

The active constituent in larvicide products used for mosquito control generally includes a bacterial toxin (Bti or Bs), an insect growth regulator (S-methoprene) or a combination of both. Their modes of action are very different, requiring application at specific stages of the mosquito life cycle in order to be effective (see table below for summary). A range of product formulations are available, including liquids, granules, pellets and briquets. 

Adulticides target adult mosquitoes and can be used in fogging activities or as a residual barrier treatment. It is important to note that adulticides are not target-specific and will kill other insects, such as bees and dragon flies, and can also be lethal to fish.

Fogging involves the application of an adulticide, generally a synthetic pyrethroid, via thermal or ultra-low volume (ULV) space spraying equipment. The mode of action of synthetic pyrethroids involves disruption of the nervous system, resulting in paralysis and eventual death of the adult mosquito. As adulticides are not target-specific, fogging is only recommended when there is an imminent public health risk associated with mosquito-borne disease transmission. There is no residual effect from these products. Fogging activities should be planned appropriately to ensure wind conditions are optimal, there is no rain and the product will not drift over wetlands or water bodies where fish may be present.

Residual barrier treatments involve application of a synthetic pyrethroid to any surface where adult mosquitoes may land. This may include internal/external building walls, eaves, fences, vegetation or foliage. If applied appropriately, the product binds well to surfaces and can provide control for 6-8 weeks. Residents can have these applications applied by a licenced pest technician. It is important to note that these products are not target-specific either, and will knock down all other insects that come in to contact with the surface. They are also toxic to fish and other aquatic fauna so should not be applied near waterways.

Management Tips for Mosquitoes

It is important to determine if the larvae collected are a species that is of concern as a nuisance or public health risk and therefore require chemical control.

Pre-treatment surveys will need to be undertaken to determine where and when application is required, ensuring the product is applied at the correct stage of larval development. Post-treatment surveys are also recommended to evaluate treatment efficacy.

Maintenance in and around the home and business needs to be carried out:

• Pot plants: Empty any water from plant pots or from the leaves of bromeliads once a week.

• Ponds and water features: Make sure you have enough fish in any ponds to keep mosquito larvae in check and keep vegetation away from the edge of the water.

• Drains and gutters: Ensure drains and gutters are flowing freely and water is not pooling. Remove leaves from gutters.

• Rainwater tanks: Rainwater tanks need to have solid, close-fitting lids on any access points and mosquito-proof meshes on all inlets and overflows (mesh less than 1 mm). This prevents access by adult mosquitoes and also prevents eggs or larvae being washed in from pooled water in the gutter.

• Swimming pools: Make sure swimming pool chlorine / salt levels are kept up and remove any leaves from the pool.

• Site drainage: If long-lasting puddles persist (longer than a week) after a period of rain, improve drainage or level the ground to prevent puddles.