Everything Everywhere Daily: History, Science, Geography & More - Mosquitoes

Starting point is 00:00:00 Throughout human history, a tiny insect has influenced wars, shaped settlement patterns, halted major engineering projects, and caused more deaths than any other animal. For most of history, no one understood why these creatures were so dangerous, or even that they were the things responsible for spreading disease. Eventually, we learned to fight back, but our efforts were middling at best. Learn more about mosquitoes, how they became one of humanity's greatest biological enemies and how we learn to fight them on this episode of Everything Everywhere Daily. New from Nespresso.

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Starting point is 00:01:49 hasn't been sharks, tigers, or venomous snakes. It's been the tiny mosquito. Mosquitoes seldom killed directly. Their lethality comes from their role as disease vectors. Mosquitoes can be found almost everywhere on Earth, from the tropics to the Arctic. Some species are remarkably cold tolerant and survive harsh winters as eggs, larvae, or dormant adults. Yet others thrive in tropical climates. Biologically, mosquitoes are insects belonging to the order Diptera.

Starting point is 00:02:21 the group of true flies. Diptera literally means two wings, because members of the group possess a single functional pair of wings. Mosquitoes belong to the family Kulikidae, which contain more than 3,500 known species. And within Kulikidae, mosquitoes are divided into several sub-families and many genera. The overwhelming majority of species that are important to human health belong to just three of these genera.

Starting point is 00:02:49 Anophiles, Aedes, and Kulex. Anopheles mosquitoes are best known for transmitting malaria. Aedes mosquitoes include species such as Aedes Aetis Aiptai and AEDs Elbiphthictus, which can transmit yellow fever, dengue, and Zika. Kulix mosquitoes are important vectors for West Nile virus and Japanese encephalitis. Despite their reputation as bloodsuckers, mosquitoes primarily survive on plant. sugars. Both male and females normally feed on nectar and other sugary plant fluids. Male mosquitoes do not drink blood at all. In most blood feeding species, females take blood

Starting point is 00:03:33 meals because they need protein and other nutrients to produce their eggs. There are exceptions, and some mosquito species can reproduce without taking blood, but the familiar mosquito bite is almost always produced by a female preparing to reproduce. The itching and swelling associated with mosquito bites are not primarily caused by the physical puncture of the skin. They are an immune reaction to proteins in the mosquito's saliva. The body recognizes these proteins as foreign and releases compounds including histamine that produces the familiar redness, swelling, and itching. Mosquitoes actually have a very short life cycle. Male mosquitoes typically live shorter than females, sometimes only a week or two, while females of some species,

Starting point is 00:04:19 can survive for several weeks or considerably longer under favorable conditions. The mosquito life cycle consists of four stages, egg, larva, pupa, and adult. The first three of those stages normally occur in water. After mating, and for many species, obtaining a blood meal, a female searches for an appropriate place to lay her eggs. Different mosquito species have evolved dramatically different preferences. Some deposit eggs directly on. on standing water. Others place eggs on damp soil or vegetation where flooding will later cause them to hatch. Basically, almost anywhere there's standing water has the potential for mosquito eggs to be laid. When the eggs hatch, mosquito larvae emerge. The larvae are sometimes called wrigglers because of the

Starting point is 00:05:09 way they move through the water. They feed on microorganisms, algae, bacteria, and bits of organic matter. Many mosquito larvae breathe atmospheric oxygen, forcing them to raise. return frequently to the surface. As larvae grow, they mold several times and eventually enter the pupil stage. Mosquito pupi sometimes called tumblers do not feed, but unlike many other species of insects, they're highly mobile. They remain aquatic while the adult mosquito develops inside. The word for mosquito comes from the Spanish, Mosca, which means fly, and the suffix Edo, which means little. So mosquito literally means little fly. The relationship between humans and mosquitoes goes back as far as history itself,

Starting point is 00:05:53 even if for most of that time, humans were unaware that it was mosquitoes that were causing a problem. Humans believed epidemics arose from environmental corruption, divine punishment, imbalances in the body, or poisonous vapors known as miasmas. Ironically, attempts to avoid swamp air, sometimes reduce mosquito exposure, without anybody really understanding why. The ancient Greeks recognized an association between fevers and swampy environments, although they did not understand mosquitoes or parasites. Medical writers from the time described reoccurring fevers that closely resembled malaria. Malaria profoundly affected some ancient societies.

Starting point is 00:06:35 Marcy regions around Rome were notorious for fevers. Seasonal outbreaks reduced agricultural productivity, killed travelers, and contributed to the abandonment of some low-line areas. The disease was so strongly associated with marshes and foul-smelling air that Italians eventually used the term Mal Aria, which just meant bad air. Mosquitoes have repeatedly influenced warfare. Historically, armies entering tropical or malarial environments sometimes lost enormous numbers of soldiers to disease. Military commanders might win battles yet lose campaigns because mosquito-borne illness debilitated. their forces. The first major breakthrough in understanding the role mosquitoes played in disease came in 1880 when the French military physician, Alphonse Leveron, observed malarial parasites in the blood of infected patients. This, for the first time, demonstrated that malaria was

Starting point is 00:07:34 caused by a living organism. The next crucial discovery came through the work of the British physician Ronald Ross. In 1897, while working in India, Ross showed that mosquitoes transatlose transmitted malaria parasites. Italian researchers, including Giovanni Batista Grassey, subsequently established that human malaria was specifically transmitted by Anophilis mosquitoes. And roughly at the same time, researchers were solving another mosquito mystery involving yellow fever.

Starting point is 00:08:05 Yellow fever had repeatedly devastated cities and armies in tropical and subtropical regions. Victims could suffer fever, internal bleeding, and vomiting of blood. During the 18th and 19th centuries, Yellow fever periodically swept through American cities, including Philadelphia, New Orleans, Charleston, and Memphis. The Philadelphia epidemic of 1793 killed thousands and caused much of the population, including members of the federal government, to flee the city.

Starting point is 00:08:34 Yellow fever was also one of the greatest obstacles to European military operations in the Caribbean. During Napoleon's attempt to suppress the Haitian revolution, diseases killed far more French soldiers than combat ever did. Similar problems also confronted workers during early French attempts to build the Panama Canal. A Cuban physician, Carlos Finley, proposed in 1881 that mosquitoes transmitted yellow fever. Much of the medical community initially dismissed or ignored his hypothesis. But nearly two decades later, the Yellow Fever Commission, led by Walter Reed, provided strong evidence supporting mosquito.

Starting point is 00:09:13 transmission. And once this mechanism became accepted, disease prevention changed dramatically. During the American construction of the Panama Canal, sanitary engineer William Gorgas organized a massive mosquito control program. Workers drained standing water, fumigated buildings, improved drainage, and treated breeding sites with oil or other substances that killed mosquito larvae. Yellow fever was effectively eliminated from the canal zone and malaria deaths. fell sharply as well. This achievement demonstrated that mosquito control could transform areas previously considered almost impossible for large numbers of outsiders to inhabit safely. The 20th century introduced chemical mosquito control on an unprecedented scale. One of the most

Starting point is 00:10:01 famous chemicals was DDT, or dichloral diphenyl trichloral ethane. Although first synthesized in the 19th century, the Swiss chemist Paul Herman Mueller discovered its powerful insecticidal properties in 1939. DDT is a contact insecticide that disrupts a mosquito's nervous system by interfering with sodium channels in nerve cells. This causes uncontrolled nerve firings, paralysis, and eventually death. DDT proved extraordinarily effective against mosquitoes and other insects. During World War II, Allied forces used it extensively.

Starting point is 00:10:39 to control malaria and insect-borne typhus. Buildings and entire communities were all treated with DDT. However, widespread agricultural use of DDT created major environmental problems. The chemical persists in ecosystems and accumulates through food chains. This became particularly notorious for causing eggshell thinning and predatory birds. Rachel Carson's 1962 book Silent Spring drew widespread attention to the environmental effect of indiscriminate pesticide use, including DDT. Many countries subsequently restricted or banned agricultural DDT use.

Starting point is 00:11:20 Modern mosquito control uses a combination of approaches rather than just relying on a single weapon. One strategy is source reduction, meaning eliminating breeding habitat. Communities will remove discarded containers, improve drainage, cover water storage tanks, and reduce unnecessary standing water. Larvicides can be applied to water that can't be easily removed. One widely used biological larvicide is produced by the bacteria, bacillus, thuringensis, Israelensis, commonly abbreviated as BTI. The bacteria produces toxins that kill mosquito larvae after they ingest them

Starting point is 00:11:59 with relatively limited effects on many other organisms when used appropriately. Adult mosquitoes can still be targeted with insecticides delivered through trucks, aircraft and handheld sprayers. Modern mosquito control programs try to use these methods selectively because insecticides can affect other insects and because mosquito populations can evolve resistances. Insecticide resistance has become one of the greatest challenges in mosquito control. Mosquitoes reproduce quickly and intense pesticide use creates powerful evolutionary pressure. Individuals carrying mutations that help them survive insecticides, reproduce, gradually making the population more resistant.

Starting point is 00:12:41 Modern repellents provide another layer of personal protection. Diet, which was developed by the U.S. military after World War II, became one of the most widely used mosquito repellents. Repellents work largely by interfering with the mosquito's ability to detect or recognize a host rather than simply poisoning the insect. Another mosquito control technique is the sterile insect method. Large numbers of male insects are sterilized. traditionally using radiation and then released into the wild.

Starting point is 00:13:12 Females that mate with sterile males produce no viable offspring, potentially reducing the population. This method can work extremely well, but only for short periods. Mosquitoes reproduce quickly, so even if you reduce the population by 99%, it can bounce right back to previous levels in just a few months. An even more powerful and controversial possibility involves gene drives. Normally an organism has a roughly 50% chance of passing a particular version of a gene to its offspring.

Starting point is 00:13:47 In particular, the sex of the offspring. Gene drive systems can dramatically increase that probability. A mutated or modified mosquito could, in theory, be released that would only create other male mosquitoes, which in turn could only create other male mosquitoes. As the population of these modified mosquitoes increased, the percentage of female mosquitoes would decrease, eventually eliminating the entire species, or at least within a certain area.

Starting point is 00:14:17 Despite how annoying mosquitoes are, there are serious concerns about completely eliminating any species. If you've ever experienced mosquitoes, you might have found yourself wondering exactly what functions do mosquitoes actually serve. Many species do not bite humans and most do not transmit diseases. Mosquito larvae form part of the aquatic food chain, consuming microorganisms and organic matter, while they themselves are providing food for insects, fish, and other organisms. Adult mosquitoes can serve as prey for spiders, dragonflies, birds, bats, and other animals.

Starting point is 00:14:54 Because both males and females consume nectar, mosquitoes also contribute to the animals. Mosquitoes also contribute to plant pollination. However, the benefits of mosquitoes can be hard to appreciate when you're constantly slapping yourself and getting bitten. Mosquitoes might be small, but few animals have had greater impact on human history. They have spread diseases that shaped wars, limited where people could settle, and killed millions, while forcing humans to develop countless techniques to fight them. The battle against mosquitoes continues, and it quite probably will never fully end.

Starting point is 00:15:29 end. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Otkin and Cameron Kiefer. My big thanks go to everyone who supports the show over on Patreon. Your support helps make this podcast possible. And I also want to remind everyone about the community groups on Facebook and Discord. That's where everything happens that's outside the podcast. And links to those are available in the show notes.

Starting point is 00:15:55 As always, if you leave a review on any major podcast app or in the above community groups, you two can have it read in the show.

Everything Everywhere Daily: History, Science, Geography & More - Mosquitoes

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