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australia:mosquitoes

Mosquitoes in Australia

Introduction

  • mosquitoes are prevalent in most areas of Australia and belong to the insect family Culicidae
  • fortunately, malaria is not found in Australia, and dengue fever is limited to the tropics such as around Cairns carried by Aedes aegypti.
  • also very fortunately, Aedes albopictus (tiger mosquito) has not yet invaded Australia although it is in Torres Strait1) and as it can tolerate cooler climates could eventually spread across Australia and bring dengue, zika and chikungunya viruses even to Victoria as it has down in most other parts of the world, and also tends to bite throughout the day.
  • nevertheless, mosquitoes in Australia can spread viral diseases such as Ross River virus and bites should be avoided where possible.
  • there are more than 275 mosquito species in Australia. Only a few species bite humans, and even less carry human diseases.
  • why insects circle lights
    • it seems most flying insects, as they do not have gravitational sensors as with larger animals, rely on the sky being brighter than the ground day and night and so they use “dorsal light response” to automatically keep their backs to the light when flying - this means when they approach a light, they bank like an aeroplane to keep their backs facing the light and this banking causes them to fly in circles around the light until they die from exhaustion or get eaten by predators. If they approach the light from above it, they end up crashing onto the ground. If they approach from under it, they go upwards then stall and crash. 2)
    • most are not actually attracted to the light itself (phototaxis) or to the heat of a flame (pyrophilic)!
    • this new 2024 research may change the design of mozzie catchers.

Do mosquitoes love you?

  • there seems to be quite a variation as to how attractive or repellent a person is to mosquitoes
  • in addition to female mosquitoes feeding on blood, mosquitoes mainly feed on plant nectar and so plant-based soap scents or perfumes can confuse them
  • the main long range attractant is increased carbon dioxide levels which from a human exhaled air are detectable from 9-10m via GRs on cpA neurons
  • medium range cues are visual and odourants “kairomones”
    • they have up to 80 types of olfactory sensory neurons, depending on the species, and three types of olfactory receptors: the odorant, gustatory, and ionotropic receptors
    • combinations of human kairomones are stronger attractants than single attractants
    • the antennal Ir8a receptors selectively recognize human odors in the presence of CO2 - some kairomones are ignored unless CO2 is detected as well
  • at close range body heat becomes a factor
  • thus body odour is one major contributor
    • every person emits their own unique odor profile, some of which were more attractive to mosquitoes than others
    • it seems what really matters to the mosquito is not the most abundant chemical, but rather the specific associations, ratios and combinations of chemicals, not only from the soap, but also from our personal body odors
    • the following affect your emitted body odour:
      • genetics:
        • “human scent kairomones like sulcatone, geranylacetone, decanal, undecanal, 2-methylbutanoic acid, tetradecanoic acid and octanal” are apparently encoded by HLA system genes 3)
        • some gene variants attract some species of mosquitoes more
      • physiologic status
        • pregnant woman attract more due to increased body heat, metabolic rate and perhaps a unique kairomone
        • those infected by malaria attract more mosquitoes due to a distinct “malaria smell” enriched for aldehydes and thioether 4)
      • the way you live
      • what you eat
        • bananas and alcohol may increase attractions
      • the places you go
      • type of soap used to cleanse yourself and erfume used
        • soaps drastically change the way we smell, not only by adding chemicals, but also by causing variations in the emission of compounds that we are already naturally producing
        • limonene is a repellent but soaps containing this can still be attractant depending upon other chemicals
        • coconut scent is generally repellent and is probably one of the safest bets when choosing a soap 5)
        • eucalyptol appears to be repellant
        • methyl dihydrojasmonate in perfumes, and isopropyl tetradecanoate in deodorants, or the smell of clothing, may mask human scent or reduce olfactory sensitivity
      • light airborne carboxylic acids, as well as another chemical called acetoin that is likely produced by the skin microbiome appear to be particularly attractant, at least to Anopheles gambiae 6)
  • use of mosquito repellents
  • type of clothing
    • mosquitoes can bite through a range of clothing including tightly fitting thin tracksuits
  • species of mosquito
  • infections within mosquitoes
    • “dengue-infected Ae. aegypti mosquitoes are more active and sensitive to kairomones” 7)
  • weather conditions
    • mosquitoes' body temperature is that of the ambient temperature so temperatures below 10degC makes them lethargic
    • they also get dehydrated in direct sun or hot dry air and will thus avoid these and wait for more suitable conditions when they can be even more hungry!
      • a stove inside a tent may thus also be a deterrent
    • heavy rain discourages them from flying
    • their preference is generally warm, humid periods when it is cloudy or the sun has set
  • proximity to smoke from camp fires may reduce mosquitoes
    • mosquitoes and most other insects avoid smoke and heat from fires but some insects are attracted to the light

Life cycle

  • only the females feed on blood which they need to develop eggs which are generally hatched some 48hrs after a feed
  • once the female has fed they will generally rest to digest her meal and develop eggs.
  • males only live about 1 week and feed on plant nectar
  • females can live to around 28 days although less than 10% of mosquitoes survive more than 10 days as adults.
  • the life cycle of eggs hatching through to adult form takes 7-14 days (which thus requires standing water to remain for that period - a flood will wash them away) with the eggs generally hatching after contact with water and eggs can survive many months of drought
    • they can tolerate organically polluted water such as septic tanks, drains, sludge pits, ground water at garbage dumps, as well as brackish water such as estuarine marshes and swamps, tidal reaches of river margins and irrigation run-off in inland areas with saline soil.
  • some species only remain near where they hatch, others travel a km or two, whereas other species can travel up to 50km downwind
  • female adults are generally most active at dawn and dusk when the air is more humid and the insects are at less risk of drying out, and will seek blood sources depending upon a range of stimuli including carbon dioxide levels, body odour, air movement or heat
  • in Victoria, mosquito numbers tend to increase after rains in Winter/Spring followed by a warm Spring with previously desiccated eggs (these may carry vertically transmitted viruses) hatching with the rains
  • most species disappear over winter

pest species which bite humans in Victoria

  • there are two primary mosquito species which play a major role in Ross river Virus (RRV) transmission in Victoria these include: Aedes camptorhynchus and Culex annulirostris. Macropod marsupials are generally regarded as key reservoir species, making Eastern Grey kangaroos (Macropus giganteus) and possums (Trichosurus vulpecula) likely reservoirs and juvenile susceptible hosts amplify transmission more so than high mosquito populations 8)

major pests

  • Aedes alternans: nuisance pest in many areas and noticed because of its size; can carry Ross River; vicious biters of humans and other animals, biting by day and night; may disperse several kilometres from larval habitat. The larval stage is predacious on other mosquito larvae.
  • Aedes camptorhynchus (aka Ochlerotatus or southern saltmarsh mosquito): a major pest in coastal areas of Vic, Tas and parts of SA and southern WA; can carry Ross River virus and this has been found in E. Gippsland and east coast Tas. can be vicious biters readily attacking humans and other animals including birds, and will feed during the day, at dusk and after sunset.
  • Aedes notoscriptus: arguably the major domestic pest species in southeastern Australia; can carry MVE, Ross River and Barmah viruses; readily attack humans by day in shaded areas but also feed during evening, night and early morning.
  • Aedes rubrithorax: (NSW, QLD, SA, TAS, WA, VIC) more common in coastal areas than the inland. It breeds in a variety of groundpools and creekline rockpools. Can be a pest in or near some bushland areas.
  • Aedes sagax: (NSW, QLD, SA, VIC, WA) a large mosquito from inland regions, and can be a major pest after flooding in summer and autumn. can carry MVE and Ross river viruses;
  • Aedes theobaldi: Can be a significant pest in irrigation areas and after floods in rural riverine areas in Murray River regions; can carry MVE and Ross river viruses; day-biting is usually apparent as the species readily attacks humans and other animals but they will bite also in the evening and at night.
  • Aedes vittiger: Can be a significant pest in irrigation areas and after floods in rural riverine areas in Murray River regions; can carry MVE;
  • Culex molestus (“London Underground Mosquito” probably arrived in Victoria in WWII with returning soldiers): can be a serious domestic pest indoors in certain areas; can carry MVE; bites at night; can be active all year round.
  • Culex quinquefasciatus: This is the major domestic pest in many urban areas, particularly as indicated by indoor biting but is mainly north of Central Highlands and into NSW. Can carry MVE. Bites in middle of the night.
  • Culex annulirostris
    • Common Banded Mosquito, has a distinctive median pale band on its proboscis and has banded legs
    • one of the most important nuisance-biting pests and vectors of mosquito-borne pathogens associated with freshwater habitats in Australia, especially around Echuca.
    • can transmit a variety of viruses including Ross River, Barmah Forest, JEV, MVE

tasmanianinsectfieldguide.com_wp-content_uploads_2021_03_img_0944-copy-2.jpg

female Ochlerotatus camptorhynchus image courtesy of Tasmanian insect field guide

Culex annulirostris image courtesy https://wrbu.si.edu/vectorspecies/mosquitoes/annulirostris

can be nuisance

  • Aedes alboannulatus: (all states) a commonly collected mosquito, particularly early or late in the mosquito season. The larvae are found in bushland ground pools and creekline rockpools. Can be a pest in bushland areas,
  • Aedes bancroftianus: (NSW, NT, QLD, SA, VIC, WA) common mosquito in inland regions, and can be a nuisance after flooding or extensive rain. can carry Ross river and barmah;
  • Aedes flavifrons: (NSW, southern QLD, SA, TAS, VIC) a large and sometimes common mosquito that breeds in bushland groundpools and can be a nuisance biter. Ross River virus has been isolated from this species but it is not thought to be a major pest.
  • Tripteroides atripes: (all states) collected occasionally from both inland and coastal regions, this species breeds in both natural (tree hole) and artificial containers. Can be a nuisance pest in some rural areas, but vector status unknown.

not usually a serious pest

  • Aedes dobrotworskyi: (NSW, VIC) found in association with sword grass.
  • Aedes nivalis: (NSW, TAS, VIC) a cold-tolerant highlands mosquito; even found in the Mt Kosciuszko area. It will bite humans, but is not often a problem
  • Aedes procax: (NSW, QLD, VIC) a common species in coastal regions and breeds in bushland groundpools. Can be a minor pest close to its breeding area, and Ross River & Barmah Forest viruses have been isolated from this species.
  • Aedes tremulus: (NSW, NT, QLD, SA, VIC, northern WA) a small species that breeds in treeholes (and artificial containers). Ross River, Kunjin & Murray Valley Encephalitis viruses have been isolated from the mosquito
  • Aedes wattensis: (NSW, NT, QLD, SA, VIC) an uncommon very small, stoutly built mosquito from inland areas. Little is known about its ecology but it probably is a tree-hole breeder. It will bite humans, but is not a significant pest and its vector status is unknown
  • Anopheles annulipes: only rarely a pest even when relatively abundant as it does not preferentially attack humans but rather bites cattle. Bites at night and could carry MVE, Ross River and even malaria.
  • Tripteroides marksae: (NSW, QLD, VIC) a smallish mosquito with a very long proboscis. Larvae breed in both natural and artificial containers. Adults are known to attack humans but rarely are they considered a serious pest. Vector status unknown.
  • Tripteroides tasmaniensis: (NSW, southeast QLD, SA, TAS, VIC) an uncommon species that breeds in natural and artificial containers. Adults are known to attack humans, mostly during the day, but rarely are they considered a serious pest. Vector status unknown
australia/mosquitoes.txt · Last modified: 2024/01/31 07:46 by gary1

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