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The Mosquito Book. Brett Ortler
Читать онлайн.Название The Mosquito Book
Год выпуска 0
isbn 9781591934585
Автор произведения Brett Ortler
Жанр Биология
Издательство Ingram
The genus name Culex (CUE-lex) is far less colorful and simply means “gnat” or “fly” in Latin12.
Even Mosquito Researchers Get Annoyed at Mosquitoes
Some mosquito researchers clearly had some pointed (ha?) opinions about mosquitoes. Want proof? The species names they chose say it all; you’ll probably recognize most of these root words, all of which are used in English: vexans14 and inundatus and abominator and excrucians and tormentor and horrida. None of them have positive connotations.
Some biologists literally agree with Anopheles’ scientific name and think that mosquitoes are worthless, even calling for the outright eradication of mosquitoes. They argue that the ecosystem would likely be relatively unaffected13.
Four Phases of Life
Like butterflies, ants and many other insects, mosquitoes go through four general stages of life: they start life as an egg, which hatches into a larva. After feeding, the larva pupates, where it transforms into an adult.
Where Do Mosquitoes Lay Eggs? Pretty Much Everywhere
Female mosquitoes lay their eggs on or near water, or in areas that will soon be exposed to water. As you might expect, that encompasses much of the U.S., and with over 150 species in the country, there’s a great deal of variation among mosquitoes.
Very generally speaking, there are two types of mosquitoes—floodwater mosquitoes and freshwater/stagnant water mosquitoes. These names are informal, and since mosquitoes are quite opportunistic when depositing eggs, some species undoubtedly fit in both categories. Still, these categories are enough to give the layperson an idea of where mosquitoes lay their eggs—and how one can avoid giving mosquitoes places to deposit eggs.
Floodwater mosquitoes
As their name suggests, floodwater mosquitoes (which includes important Aedes species) lay their eggs in areas that are damp or that will be inundated by water, such as salt marshes or riverside forests. The eggs need to be inundated by water before they hatch, but reduction of dissolved oxygen in the water is the most important factor for egg hatching15. When levels drop beyond a certain point, the eggs hatch. This ensures that the larvae will be born into the shallow, food-filled areas where the larvae thrive. These mosquitoes often become a scourge after river flooding or the storm surge of a hurricane.
Freshwater and Stagnant Water Mosquitoes
Some species, like the malaria-bearing Anopheles mosquitoes, only lay eggs on freshwater, whereas the notorious pest Culex pipiens lays eggs16 in stagnant water, everywhere from cesspits and plant pots to hoofprints in cow pastures. The invasive Asian tiger mosquito will deposit eggs nearly anywhere it can—and doesn’t venture far from where it hatches, so if a female of a pest species deposits eggs in the birdbath on your deck rail, you’re certainly on the dinner menu17. Perhaps surprisingly, flowing streams and deep ponds and lakes are often less ideal environments for most mosquito species, as they have less food, too much turbulence and more predators.
How opportunistic are mosquitoes when finding a place to lay their eggs? During a study in the 1930s, a cage holding research mosquitoes and eggs was inadvertently torn open. When the researchers returned and discovered the damage, they noticed that some mosquitoes had escaped, but wild females had entered the cage and laid additional eggs18 !
To make matters more complex, some mosquitoes are often referred to as “container” mosquitoes because they are found in a variety of natural or artificial containers. Mosquitoes found in natural containers are often referred to as “woodland” or “treehole” mosquitoes because they are found in wooded areas, and often deposit eggs near trees—or in cavities within them. When it rains, these holes fill in with water, and the eggs then hatch. There are many types of natural cavities—from rotting stumps to containers as specific as a particular type of pitcher plant. In fact, some mosquito species even lay their eggs in pitcher plants, which serve as natural cavities and catch rainwater19. An African Aedes species even lays its eggs on the legs of crabs, which then transport the eggs to the crab’s nest, where the eggs later hatch20.
Of course, many21 mosquitoes are just as comfortable depositing eggs in artificial containers such as gutters, tarps, birdbaths and old tires. Oddly enough, many disease-transmitting mosquito species have been found developing in artificial containers in cemeteries. The vases, toys, and flowerpots left behind by mourners prove to be ideal habitat for these sometimes-deadly insects22.
Eggs: Laid Alone or Together?
In North America, there are two primary ways that mosquitoes lay eggs: some mosquitoes, including all of the Anopheles and Aedes species, deposit their eggs one-by-one, either on the water or on moist soil at the water’s edge, whereas nearly all23 Culex species (and those of a few other groups) glue their eggs together to form an egg raft, which floats on the water and rebounds to the surface when submerged.
When female mosquitoes build an egg raft, they are nearly totally committed. According to the observations of one researcher, Culex females were so focused on building an egg raft that one could be picked up from the surface and didn’t try to fly away24. Talk about a maternal instinct!
Waiting It Out: Dormancy
If the conditions aren’t right, the eggs of some species can become dormant; dormancy can last for some time—the eggs of some Aedes species25 can remain viable for up to four years. When floodwater eggs are laid in cooler weather, the eggs remain dormant until the weather warms. This is also why Dengue fever and other diseases carried by Aedes mosquitoes often spike in spring or during the monsoon season in tropical areas.
Whereas most mosquito females simply deposit their eggs and leave, one species in South America actually broods its eggs, protecting them until they hatch26. While this is common in other insects, it’s the only mosquito species known to do so.
The Eggs Hatch and Larvae Emerge
Mosquito eggs usually hatch within a few days, but under ideal27 conditions, some species can hatch within just 30 hours. Larvae are colloquially referred to as “wigglers” thanks to their wiggly swimming motions. Larvae have two primary jobs: eating and molting. Larvae go through four molting periods, each of which is referred to as an “instar.” After hatching, the larva is in its first instar. Once it molts, it is in the second instar, and so on.
With each molting period, they get larger. Of course, to grow, they need food, and eating is their specialty. Larvae are almost always filter feeders and eat a variety of algae, single-cell organisms and plant material. In some Culex species, larvae are fierce predators, consuming many larvae of other mosquito species, and even members of their own species28.
The length of the mosquito’s larval stage depends on the species and the conditions but is usually a matter of 7–10 days29.
Let’s Go Snorkeling!
All mosquito larvae are aquatic, but they