Cameron Webb/NSW Well being Pathology, Creator supplied
Summer season evenings by the pool, lake or BBQ imply mosquitoes. However what about throughout winter once we’re largely indoors? Because the climate cools, these bloodsucking pests are hardly ever seen.
However the place do they go?
Heat, moist situations go well with mosquitoes
Mosquitoes have advanced life cycles that depend on water delivered to wetlands, flood plains, and water-holding containers by seasonal rainfall. Relying on whether or not we’re experiencing a summer season beneath the affect of El Niño or La Niña, mosquito populations will change in several methods.
Throughout hotter months, their life cycle lasts a few month. Eggs laid round water hatch and the immature mosquitoes undergo 4 developmental levels. Larvae then change to pupae, from which an grownup mosquito emerges, sits briefly on the water floor, after which flies off to buzz and chunk and proceed the cycle.
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Water is essential however temperature is basically necessary too. Not like warm-blooded animals, mosquitoes can’t management their very own physique temperatures. The hotter it’s, the extra lively mosquitoes might be. There’s often extra of them about too.
However as soon as chilly climate arrives, their exercise slows. They fly much less, they don’t chunk as typically, they reproduce much less, and their life cycle takes longer to finish.
Temperature additionally performs a job in figuring out the flexibility of mosquitoes to unfold viruses.
Chilly climate isn’t nice for mosquitoes however tens of millions of years of evolution have given them just a few tips to outlive.
Ponds and puddles could also be frozen however that doesn’t imply all mosquitoes have disappeared.
Tom Keldenich/Unsplash, CC BY
Mosquitoes don’t disappear fully
On a sunny afternoon in winter, it’s possible you’ll discover the occasional mosquito buzzing about in your yard. Not as many as in summer season however they’re nonetheless round.
Some mosquitoes do disappear. For instance, the exercise of the pest mosquito Culex annulirostris, thought to play an necessary function within the unfold of Japanese encephalitis virus in Australia, dramatically declines when temperatures begin dropping beneath 17.5℃.
Research in Sydney have proven some mosquitoes, similar to Culex annulirostris, disappear. Others, similar to Culex quinquefasciatus and Culex molestus, stay lively all through the winter. You simply could not discover them (until they enter your own home to buzz about your ears).
Some mosquitoes, such because the widespread Aedes notoscriptus, could often be seen buzzing about in winter.
Cameron Webb/NSW Well being Pathology
Mosquitoes can disappear into diapause
We’re conversant in the thought of mammals hibernating by way of winter however mosquitoes, like many different bugs, can enter a section of inactivity known as diapause.
As soon as chilly climate arrives, grownup mosquitoes discover hiding locations similar to tree hollows and animal burrows, throughout the cracks and crevices of bushland environments, or in garages, basements or different constructions round our houses, suburbs and cities. These mosquitoes could solely reside just a few weeks throughout summer season however going into diapause permits them to outlive many months by way of winter.
Mosquitoes can be present in frozen our bodies of water, whether or not it’s a bucket of water in your yard or a close to freezing wetland. For instance, there’s a group of mosquitoes that belong to the genus Coquillettidia whose larvae connect to the submerged components of aquatic crops and might survive the chilly winter temperatures. Their growth dramatically slows they usually’ll keep within the water till spring arrives.
By going into ‘diapause’ adults can survive in locations like tree hollows for the chilly months.
Unsplash/Pat Whelan, CC BY
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All their eggs in a single winter basket
Some mosquitoes make it by way of the winter because of their eggs. Mosquito eggs will be extremely resilient. They survive being dried out in sizzling and salty coastal wetlands throughout summer season but in addition frozen in snow-covered creeks in winter.
In coastal areas of Australia, eggs of the saltmarsh mosquito (Aedes vigilax), sit completely safely on soil. As soon as the climate warms and tides herald water to the wetlands, these eggs might be able to hatch.
There’s additionally a particular mosquito in Australia generally known as the “snow soften mosquito” (Aedes nivalis) whose eggs survive beneath snow and hatch as soon as that snow melts and fills ponds, creeks and wetlands all through alpine areas.
Does it matter the place mosquitoes go within the winter?
It additionally isn’t simply the mosquitoes that survive the chilly months. Viruses, similar to Japanese encephalitis virus or Ross River virus, can survive from summer season to summer season in mosquito eggs, immature levels, or diapausing adults.
Realizing the seasonal unfold of mosquitoes helps well being authorities design surveillance and management packages. It might assist perceive how invasive mosquitoes survive situations in Australia exterior their native ranges by hiding out from the chilly, similar to in rainwater tanks.
Even mosquitoes sometimes present in tropical places may even adapt to cooler climates.
This data could even expose the chilly chink in mosquito’s armour that we are able to use to raised management mosquito populations and cut back the dangers of illness outbreaks.
Cameron Webb and the Division of Medical Entomology, NSW Well being Pathology, have been engaged by a variety of insect repellent and insecticide producers to offer testing of merchandise and supply skilled recommendation on mosquito biology. Cameron has additionally obtained funding from native, state and federal businesses to undertake analysis into mosquito-borne illness surveillance and administration.
