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Mosquitoes: Can we get rid of them, and what would happen if we did? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.
Answer by Matan Shelomi, Entomology, Biology, Evolution, on Quora:
Mosquitoes: Can we get rid of them, and what would happen if we did? This is easily the most common question type I'm asked to answer, in various forms. “What’s the point of mosquitoes?”, "What role do mosquitoes play in the ecosystem?”, “Should we get rid of all the mosquitoes?”, “Could we get rid of all the mosquitoes?”, “How do we get rid of all the mosquitoes?”, “Is anyone trying to get rid of all the mosquitoes?”, “Why haven’t we gotten rid of all the mosquitoes?”... And so on and so forth. In addition to mosquitoes, we see the same questions asked about “flies” and cockroaches, maybe bedbugs and fleas, and non-insects like ticks. Merging all these questions or answering them all would take forever, so I decided to write the answers to all of these questions together. We’ll focus on mosquitoes, because the facts for them can be applied to the other pests as well.
It's strange to hear people so eager to cause an extinction for once rather than prevent it, right? This hatred is not just because mosquitoes are annoying. Mosquitoes are arguably the deadliest animal in the world to humans, and I'm including other humans. They spread, or vector, diseases like malaria, yellow fever, dengue, chikungunya, West Nile Virus, and Zika virus, which together cause more deaths each year than war and homicide combined. Eliminating these diseases would save millions of lives, and eliminate much suffering and disability as well. Without the mosquitoes, these diseases would cease to exist… but why is that?
Do we need to kill all the mosquitoes?
No, because not all are bad. Mosquitoes are a fly in the family Culicidae, and there are over 3500 species of them! The females lay eggs usually in still water, anything from a shallow pond to a flowerpot or birdbath or puddle. The larvae live in the water, eating microbes and small particles or algae. They pupate in the water, and the adult mosquito eventually emerges from the water surface and flies off.
What do adult mosquitoes eat? Most are vegetarian. They drink flower nectar, plant sap, and fruit juices, and never drink blood. Killing these species is not necessary: in fact, it’s counterproductive. The more than 90 species of one such harmless genus, Toxorhynchites, also known as the “elephant mosquito” because of their great size, are an ally to our cause: their larvae eat other mosquito larvae! Since they are helpful, we should make sure any strategies we use to kill bad mosquitoes will leave these gentle giants alone.
Of the mosquitoes that do suck blood, only a few (200 or so) feed on humans. Others only feed from birds or lizards or smaller mammals, and many of those that do bite humans would prefer feeding on something else. Of those that can feed on humans, not all carry human diseases, and even in the species that do, not all strains are efficient vectors. Also, different species carry certain diseases. For example, Plasmodium, the protozoan parasite that causes malaria, is spread almost exclusively by mosquitoes in the genus Anopheles. Of the about 460 species of Anopheles mosquito, only a hundred or so can actually carry the five or so species of Plasmodium that infect humans [out of over 200 species of Plasmodium that infect other animals]. Of this hundred, only three or four dozen are good enough vectors to pose a risk to humans, and only a handful of these actually prefer humans as a blood source, and only five carry Plasmodium falciparum, the one species of malaria responsible for the worst symptoms and most deaths. Of these, the worst is Anopheles gambiae, although this is technically a species complex of at least seven different species… but that's another story. In summary, if you want to destroy malaria, there are only a few species that matter the most, and focusing on An. gambiae is the priority. Killing this one species [complex] alone would save millions.
A few other genera carry other disease agents, namely arboviruses (short for arthropod-borne viruses). Many species in the genus Aedes, but especially Aedes aegypti and Ae. albopictus, vector arboviruses such as dengue virus, yellow fever virus, Zika virus, chikungunya virus, West Nile Virus, La Crosse virus, and some animal viruses such as Western equine encephalomyelitis virus. Many of these viruses are also spread by species in the genus Culex, which also spreads bird malaria, and the genus Culiseta, which rarely bites humans, and Ochlerotatus [there is controversy over this genus name that I won't get into here]. The genus Haemagogus spreads yellow fever and some rarer viruses called Mayaro and Ilheus viruses. The genus Mansonsia can spread some arboviruses, but are more important for spreading roundworms that cause filiariasis in Asia and the Pacific. The other genera also have roundworm-vectoring species, responsible for the spread of heartworm in dogs and other animals and lymphatic filiariasis and elephantitis in humans.
Why are some species better vectors than others? The answer is because mosquitoes don’t just carry diseases: they get sick from them. When the mosquito swallows infected blood, its own midgut gets infected. The pathogens replicate in the midgut and burst out into the body cavity, where they eventually infect the salivary glands. The whole process takes up to two weeks depending on the disease. When mosquitoes bite their next victim, the pathogen is injected with the saliva. This is one reason why HIV, the virus that causes AIDS, is not vectored by mosquitoes: it cannot infect the mosquito midgut and just gets digested away. Different mosquito species may be immune to certain pathogens, have resistant midguts or resistant salivary glands, or may simply die of natural causes before the pathogen can complete its replication cycle and reach the salivary glands. Infected mosquitoes do sometimes have shorter life spans, so evolution keeps the diseases in check: they cannot kill the mosquito before they've finished incubating and have been injected into a new host.
In summary, we don't need to kill all the mosquitoes. Just the vector species.
What do mosquitoes do for the world?
Do mosquitoes serve a purpose other than spreading disease? More importantly, do the vector species have a role that makes them worth keeping around?
Let’s start with the larvae. Living in the water and eating detritus, they do keep the water somewhat clean, but so do lots of other organisms that aren't disease vectors. So mosquito larvae don’t eat anything important… except for the Toxorhynchites larvae that eat other mosquito larvae, and we’ve already agreed that we’ll be sparing this genus from genocide.
What eats the larvae? Other aquatic larvae do, such as dragonfly and damselfly nymphs, as well as some turtles and large tadpoles and fish. The most famous predators of mosquito larvae are Gambusia affinis and Gambusia holbrooki, better known as mosquitofish. Native to the USA, they are commonly introduced to ponds and pools as a mosquito control, with some governments giving them out for free, with the assumption that they will eat the mosquito larvae rather than anything else. This worked wonders in some parts of the world, especially near the Russian city of Sochi, formerly a malaria hotspot; a statue of the fish was erected there in gratitude in 2010.
However, the assumption is incorrect, and the common name a misnomer. G. holbrookiactually prefers plankton, algae, and detritus [the same foods as larval mosquitoes], and mostly switches to invertebrates like mosquito larvae when it really has no choice. G. affinis is a better predator, capable of eating half to one-and-a-half times their own body weight in mosquitoes every day. However, they cannot live on mosquitoes alone, but actually suffer malnourishment and stunted growth, and must eat other foods too like plankton and other insects. Despite their name, they only eat mosquitoes as a small part of their normal diet. Worse, they are extremely aggressive towards other fish, which themselves are often just as effective at eating mosquitoes. In Australia, mosquitofish deliberately introduced in the 1920’s and 30’s bullied or outcompeted native fish and frogs and reduced their numbers to such an extent that mosquito numbers actually went up, because there were fewer predators overall. That the fish and frogs and native insects being killed or eaten by the mosquitofish were themselves important species now threatened by extinction meant introducing the mosquitofish would have been a bad idea even if they did fight mosquitoes. Sochi was spared this disaster because they didn’t have many native fauna to be threatened by the mosquitofish to begin with. The possibility exists that introducing another fish, like a catfish or even goldfish, would have worked there just as well. Clearly, Gambusia is not a reliable ally in the global mosquito extinction campaign, but on the other hand we need not worry about losing fish if the mosquito larvae die off, since no fish [or other animal] depends on them exclusively.
What about adult mosquitoes? They’re food for an even greater diversity of creatures, from fish and frogs to salamanders and lizards to venus fly traps and birds and bats, not to mention other insects… but not, by the way, the "mosquito-hawk." That's a name given to crane flies, which not only don't eat mosquitoes but also don't eat anything at all: the adults have short lifespans and don't bother feeding. The insects that do eat adult mosquitoes include dragonflies and damselflies, with the benefit that their aquatic nymphs also eat the aquatic mosquito larvae and pupae. They are the mosquitoes’ lifelong nemesis.
Could these natural predators be used to eradicate mosquitoes, and would eradicating mosquitoes harm these predators? No and no. Again, the mosquito is not the only animal eaten by any of these creatures. A great example is the Purple Martin (Progne subis), a rather handsome, insectivorous, American bird commonly promoted as a viable biocontrol against mosquitoes, but possibly overhyped. Multiple studies have looked at its feeding habits, and found that mosquitoes are not a big part of its diet, that their feeding ranges and times do not overlap with when and where vector mosquitoes are active, and that Purple Martin releases have not had big effects on local mosquito populations [though some contradictory studies exist]. Also, like Gambusia, the Purple Martin can make the situation worse because it eats other predatory insects like dragonflies, as well as other insects across the harmful/helpful spectrum from beetles to bees. Dragonflies themselves will also happily eat honeybees and butterflies in addition to mosquitoes, gnats, midges, and flies. The same applies for bats, where mosquitoes may make up less than 1% of their diet. Can you blame these predators? Mosquitoes are tiny, barely a mouthful, while a fat beetle or chubby moth is much more nutritious snack.
What if these alternative food sources did not exist? Is there any part of the world where mosquitoes are a dominant insect? Yes: the arctic. While most insects prefer warm weather, and the tropics have the greatest insect diversity overall, the arctic tundra actually has the biggest mosquito problems in the world, because the land there is a perfect incubator for mosquitoes. The soil is near frozen all winter, but in the summer it thaws, making entire fields one gigantic breeding ground for mosquitoes. Mosquito swarms reach biblical proportions in these regions, forming thick, dark clouds of insects. Scientists believe the mosquitoes are a critical part of the diet of birds in these regions… but others disagree, claiming native midges (related flies from the family Chironomidae) are actually a bigger part of the native birds’ diets and would fill the gap left by mosquitoes. Thus the birds of the arctic are the most likely and perhaps only creatures that could lose a major food source without mosquitoes. Fortunately, the dominant mosquito species in the arctic are Aedes impiger and Aedes nigripes, neither of which vectors human diseases. So if our goal is to fight vector species, we could leave the arctic alone.
What about pollination? Are any plants mosquito-pollinated? Yes, many, but most of these are pollinated by other insects as well, such as goldenrod. A few plants do exist that are preferentially mosquito pollinated, meaning other insects can pollinate them but mosquitoes are the most common and most efficient. All are orchids, namely cold-temperature ones. An example is Platanthera obtusata, the blunt-leaved orchid found across the Arctic, pollinated by mostly female Aedes mosquitoes as well as a few moths. It attracts mosquitoes by giving off a faint scent, detectable by mosquitoes but not our own noses, that is very similar to human body odor. The related Platanthera flava is also pollinated by Aedes primarily and small moths secondarily. Other Platanthera species are pollinated by mosquitoes secondarily and other insects primarily, or are mostly self-pollinating and rarely require insect help, and a few other orchid species have similar cases. Loss of some of these orchids is thus a risk of loss of mosquitoes. However, none of the orchids are important to the ecosystem itself, nor are they important to humans: the world will live on without them. That’s not to say the rather large problem of orchid extinctions isn’t serious, but the problem of insect-vectored disease is arguably worse.
What are the risks of eradicating mosquitoes?
As you noticed, there are no keystone species in mosquitoes. No ecosystem depends on any mosquito to the point that it would collapse if they were to disappear. An exception may be the Arctic, but the species there are non-vectors and thus can be left alone.
Granted, we are making assumptions here. We certainly do not know all the myriad ways all mosquitoes interact with all life forms in their environment, and there may be something we are overlooking. Non-target extinction isn’t the only problem: there’s also the possibility that the gap (technically an ecological niche) left behind by mosquitoes will be filled by something even more annoying, though likely non-vectoring. The worst scenario is one vector mosquito species will replace another, and the most likely scenario is mosquitoes will be replaced by midges. They also have aquatic larvae and the females of some also blood-feed, some on humans. The combination of fewer mosquito competitors and possibly fewer predators of mosquitoes could mean an explosion of midge populations. On the other hand, the predators now reliant on mosquitoes may eat more midges instead, causing the populations to reach a stable equilibrium after a while. Are midges dangerous? Those in the family Chironomidae do not bite, but those in the family Ceratopogonidae do, and not only can their bites be itchy for as long as week, a few do vector human and animal diseases [though not human malaria or yellow fever as far as we know].
Another surprising way mosquitoes can affect the ecosystem comes, again, from the arctic. Mosquitoes control the migrations of woodland caribou (Rangifer tarandus caribou). Their massive herds in Canada are always on the move to find food, but in the summer they travel a lot more, covering greater distances and moving to higher ground, sometimes avoiding the best feeding sites, because they are trying to avoid the gigantic swarms of mosquitoes that plague the Arctic regions in the summer! All the time spent running and not eating means they build up less fat that they would need for the cold winters, which can often mean death. Killing off these mosquitoes would change the historic caribou historical migration routes, with unpredictable consequences. On the other hand, caribou populations today are a fraction of what they once were, down to several thousands from several hundreds of thousands due primarily to human habitat destruction, so more caribou would be a good thing. The caribou are clearly are bothered by mosquitoes, losing up to a liter of blood a week during the worst outbreaks, so if asked I’m sure they’d vote for eliminating mosquitoes, and given their population size and herd mentalities they’d likely come out to vote in large numbers.
Truly worst-case scenarios are unlikely, considering that we’ve eradicated many malaria mosquitoes from parts of Europe and North America without trouble, but they are still possible, so any extinction or extirpation [a local extinction from a smaller area, not the entire planet] has unforeseen risks. The question is: are the risks of maybe altering an ecosystem worth human life, and how much? We are not arguing over whether or not to save the panda, but to eliminate the greatest killers humanity has ever known. Given that arboviruses and malaria currently are killing or affecting millions, to not eradicate the vector mosquitoes responsible could only be justified if the expected environmental effects would be similarly damaging. We cannot poison an entire rainforest to fight yellow fever, because millions of people depend on that rainforest for food, medicine, wood, employment, clean water, and clean air: the cure would be worse than the disease [literally] and affect more people. On the other hand, say we eliminate Aedes aegypti and a salamander species and an orchid are eliminated along with it: that is a trade we can live with, and by “we” I mean the millions who will no longer die from yellow fever. The other extinctions will be a tragedy, yes, but the loss of yellow fever will be a triumph worthy of the Nobel Peace Prize. Compared to the losses of the dodo and the Tasmanian tiger, which came with no benefit to society and are thus completely unfortunate, the benefits of the loss of Ae. aegypti or An. gambiae would outweigh even the most pessimistic estimates of costs.
How could we kill all the world's vector mosquitoes?
Because tampering with ecosystems is so tricky, it is important not to use methods that are too broad. It’s hard enough to predict the effects of killing one species: imagine having to factor in the loss of any species accidentally killed in the process… assuming we can even predict them all! So pesticides are out: they have non-target effects, and, besides, they won't work on a global scale. Aerial sprays won't hit the mosquitoes that like to bite indoors, and putting oils or insecticides in breeding sites won't catch the many, many tiny breeding sites in peoples' properties: everything from a tree hollow to a bit of rainwater sitting in a discarded plastic bag is a potential mosquito breeding site. That's why public participation is important in mosquito control: everyone must do their part to clear the breeding sites in their backyards. Alas, if even one is missed, the mosquitoes will return.
No, if we are going to eradicate mosquitoes worldwide, we need a method that is species specific, unstoppable, and inescapable. Something guaranteed, by way of design, to affect only the target organism, and to be impossible to adapt to or evolve resistance against. We need autocide, where the species is unwittingly responsible for its own death. Is such a thing even possible?
It is, and it has been done. The New World screw-worm fly (Cochliomyia hominivorax), also known as the screw-worm, is a parasitic fly whose maggots infest the healthy tissue of warm-blooded mammals. This includes humans, but the bigger problem is cattle, where the worms cause death within ten days. In the 1950’s, losses in the USA due to screw-worm were over US$200million a year. Something needed to be done, but pesticides were not working. Scientists studied the screw-worm intensively, including a $250000 study partly on the sex-lives of screw worms that was widely decried by US senators as wasteful spending of taxpayer funding. They would later eat their words with an American-grown steak and a glass of milk. It turns out that female screw-worms are monogamous, only mating once in their lifetime. Scientists Edward Knipling and Raymond Bushland reasoned that if a female screw-worm mates with a sterile male, her eggs will never hatch, and since males mate repeatedly, one sterile male can not-impregnate multiple females. Thus, if one floods an ecosystem with a large enough number of sterile males [which have no effect on cattle, because males don't drink blood or lay eggs], they will out-mate the healthy males and the number of fertile matings is reduced, instantly reducing the size of the next generation. This process is repeated constantly until eventually every female mates with a sterile male, at which point the population is wiped out… forever.
This sterile insect technique (SIT) was tested with screw-worms in the 1950’s using X-rays [later gamma rays and other techniques] to sterilize flies mass-reared on ground meat in the lab, irradiating them at the pupal stage just enough to sterilize males without making them too weak to compete with normal males. Long story short, it worked. By releasing large numbers of sterile male flies over several weeks at a time, SIT successfully eliminated the screw-worm from the USA, then Mexico, working southwards until all of North and Central America was cleared of the flies. When screw-worm was accidentally imported to Libya in 1988, sterile males were eventually brought in on December 1990 and eradicated the screw-worm in less than a year. Sterile screw-worm males are still released in Panama periodically, forming a biological wall against any females from the South. The results saved the US cattle industry alone over $20billion and counting, winning its authors the 1992 World Food Prize and being declared “the greatest entomological achievement of (the 20th) century.”
The principles of SIT make sense for safely eliminating vector species, since there are no other effects on the environment other than those caused by the loss of the species itself, and it only works on a single species at a time: SIT against Aedes aegypti won’t have an impact on Aedes impiger, let alone other genera of mosquitoes, let alone other insects, let alone mammals or people. Many mosquito females are also monogamous, so SIT could work in theory. Plus, since only the vegetarian male insects are released, one can unleash billions of these mosquitoes in an area and there won’t be a single extra insect bite. SIT has been successfully used to eradicate tsetse fly (Glossina spp., the vector of African Sleeping Sickness) in parts of Africa, and several have tried it against mosquitoes… but many failed. Efforts to eliminate Anopheles quadrimaculatus in Florida, USA over nearly a year had no effect, because the sterile males simply could not compete with the normal ones and were not chosen by mates. This happened again for Culex tarsalis in California. The problem is the radiation can weaken mosquitoes and/or lower their lifespans, so they fail to attract females. Not all insects respond well to irradiation, which limits the subjects SIT can work with.
An alternative strategy is cytoplasmic incompatability, which sounds more complex than it is. Instead of radiation the mosquitoes are infected with a bacteria called Wolbachia that lives inside insect cells, including egg and sperm cells. When Wolbachia-infected sperm combine with uninfected eggs, the egg dies. Guaranteed. Culex quinquefasciatus was successfully eliminated from the city of Okpo in Burma in 1967 in 9-weeks with this method. However, this technique won’t work if the wild mosquitoes alsoare infected with Wolbachia: if both egg and sperm are infected with the same strain, or even if the egg is infected and the sperm not, the embryo lives and becomes a new male or female whose eggs will also be immune. It also doesn’t solve the problem that rearing at large densities in a facility is itself stressful: studies with Anopheles gambiae showed those reared at higher densities were less like to win mates than those reared at lower or natural densities. Large numbers of mosquitoes need to be produced cheaply, but if one cuts too many costs they won’t be effective competitors for wild males and will fail to mate.
There’s another problem: since we don’t want to release blood-sucking female mosquitoes, sterile or otherwise, we need a good way to eliminate females in the lab from the irradiated pool before they are released. Unfortunately, the sex ratio for mosquitoes is 50/50, so a way of separating males and females is needed. The ones used at first could not be more primitive: Male and female mosquito pupae are slightly different colors and sizes, so someone manually or a machine with a strainer had to sort them and ensure only males get sent to be irradiated and released. Unfortunately, this does not work for Anopheline mosquitoes, because the pupa sizes overlap. Even before this point, though, money has been lost. Both males and females require the same resources in lab, so inevitably no more than half the insects raised in an SIT program will ever be released, making everything twice as expensive as it should be. Since a huge number of sterile males is needed to have any effect, these high costs are a problem for a global extermination program.
Is there some way to ensure only males are produced, or a way to kill off unnecessary females earlier? Yes, using genetic sexing strains (GSS), an old technique in which a dominant selectable marker—a gene that makes its possessor able to survive an otherwise lethal challenge— is attached to the male sex chromosome. A successful example is the aptly named MACHO: a strain of An. albimanus with an insecticide-resistance gene attached to the male chromosome (mosquitoes mostly have an XY sex-determination system like humans do, where only males have a Y-chromosome). Treating a batch of MACHO eggs with insecticide will kill 99.9% of all females, allowing a million mosquitoes per day to be released when it was used to control mosquitoes in El Salvador in the late ‘70’s. In case you are wondering, the eradication almost worked, until the mosquito immigrated back in from another country. Whatever technique we choose, it would need to be global, and in any case GSS doesn’t solve the problem that irradiation can make many mosquitoes weak competitors.
The latest advance skips irradiation all together. It is called RIDL, short for Release of Insects carrying Dominant Lethals, invented by entomologist Luke Alphey. In RIDL, the males are not irradiated, meaning they are just as healthy and competitive for mates as wild males, but also they will produce viable eggs. So instead they carry a lethal gene that causes their larval offspring to die before reaching blood-sucking adulthood. The current form of RIDL involves a gene called tTAV (tetracycline repressible activator variant), which makes a nontoxic protein that clogs up the insect’s cell machinery so no other genes are activated, causing death. The system only works in the mosquitoes’ own cells, and the protein is degraded when eaten, so there is zero effect to animals that eat the modified mosquitoes or their larvae: It is a completely nontoxic system. “But wait, how do these mosquitoes survive to adulthood in the lab?,” you ask. The answer is Tetracycline, a common antibiotic that is also the antidote to tTAV. In the rearing facility they are fed this antidote so they can live to adulthood, but in the wild they and their offspring have no hope. RIDL is currently being used to fight mosquitoes in the southern US and South America, where they have already caused massive declines in dengue mosquitoes, and are now being deployed to stop the Zika epidemic in Brazil.
A new technique, currently developed for the Mediterranean fruit fly but perhaps one day available for vector mosquitoes, is a female-specific RIDL. In this system, males carry a gene for a protein that, in absence of the antidote, only kills females. In this system, females mated with the modified males will produce perfectly viable eggs, but the female offspring die as larvae, and only the male offspring will survive into adulthood. These males still carry the modified gene, and go on to mate with the now smaller population of females, etc. In this scenario, one need only release the males once to start a chain reaction that works through the population, reducing it with every generation.
RIDL is an amazing strategy, with no harmful effects on the environment or on non-target organisms, and it even saves humans from having to work with radiation. Alas, it involves genetic modification, which means the mosquitoes are technically a GMO, which means the usual suspects are out in force trying to stop them, some spreading rather creative lies, and the media is often unable or uninterested in sorting fact and fiction. Most stories worry about the mosquitoes flying and biting local people. Some articles claim the mosquitoes vaccinate humans against diseases, which would be amazing if it was true, but it isn’t. Others claim the mosquitoes will mutate you if they bite you, which is equally ridiculous. Some are even claiming that microcephaly isn’t caused by Zika virus but by the released mosquitoes, calling it “loose gene syndrome." Never mind that such a condition does not exist and is biologically impossible; the fact that these people are willing to deny the very real problem of Zika-induced microcephaly in order to scare people off GMOs and better sell their overpriced organic produce in stores is a truly nasty appropriation of real human suffering. Fortunately, you now know the one important fact that thoroughly contradicts almost every mistake and lie ever written about insect releases: male mosquitoes don’t bite people. They don't drink blood, but actually avoid humans, and since only male mosquitoes are ever released, the idea that a released insect can harm a human is pure fiction.
Will these techniques mean we can get rid of pesticides and insecticides forever? Not quite yet. Remember that SIT and RIDL require the released males to outnumber the native males. No matter how efficiently we can rear sterile or modified males, if the wild populations are too high then these techniques will never be practical. Instead, we would need pesticides to bring down the wild populations first, to a threshold at which SIT or RIDL will work. In addition, if we want to rid the entire planet of these species, the releases would need to cover their entire ranges, which could be a massive amount of space. Still, progress is good, and even if we don’t eliminate all the vector mosquitoes in the world, we have already made a massive dent in the death toll of mosquito-vectored disease worldwide.
But wait, there's more! There is one technique that can eliminate the pathogen without harming the vector or the environment in any way, and does not require releasing or raising insects. First, let me introduce you to Chagas disease, caused by the protozoan Trypanosoma cruzi which is vectored by kissing bugs in the subfamily Triatominae, the most serious vectors being Triatoma infestans and Rhodnius prolixus. They are called “kissing bugs” because they like to bite near the mouth to suck blood. They also have the filthy habit of defecating right after they eat, and when humans scratch the bite they scrape the parasite-infested poop into the wound, infecting themselves. Charming, and also deadly, as Chagas disease can cause symptoms such as an enlarged heart. SIT has been tried in these species, but the new technique is called paratransgenesis. Rather than genetically modify the insect to make a protein (transgenesis), one modifies a symbiotic microbe that lives inside the insect instead. In the case of Rhodnius prolixus, all individuals have a symbiotic bacteria, Rhodococcus rhodnii, that makes vitamins for them that are otherwise absent in their blood-based diet. Genetically modifying bacteria is easy, so scientists created transgenic symbionts that produce proteins toxic to the Trypanosome. If you feed Rhodnius some modified Rhodococcus, the insect now became immune to Trypanosoma cruzi, unable to vector it anymore. The bacteria can be produced in large numbers easily, bypassing a problem with insect release. Best of all, the infected adult kissing bugs pass the bacteria on to their offspring: young triatomines often eat the feces of the adults, inoculating themselves with the Rhodococcus bacteria. [In case you are wondering, the bacteria can’t survive in our bloodstream, so they can neither harm us nor help us.] The system is quite promising, involving spreading Rhodnius poop infected with modified Rhodococcus everywhere Trypanosoma is a problem, with the end result that only the parasite dies out, while the insect is left alive, and the ecosystem is not affected at all. Paratransgenesis could be applied elsewhere, and scientists are working on developing it for other species, such using a modified fungus to make Anopheline mosquitoes immune to malaria.
You now have a clear idea of the many issues that go into whether or not a species should be eliminated, and whether or not that is even practical. If you have such a question for another insect, like fleas or roaches, maybe you can answer the question yourself! Ask yourself: Which species from the group are the real problem? What do they do in the world? Are males and females both a problem? Is SIT practical? Is there an alternative solution to the disease? If questions like these interest you, consider a career in medical entomology, epidemiology, genetics, or [of course] medicine, and maybe that Nobel Prize I mentioned will be yours.
What should we do in the meantime?
Global extermination of vector mosquitoes, whether or not it is doable and whether or not it is a good idea, is a long way off. Until then, the best strategies are to do local extirpations. If you have a pond, add goldfish, koi fish, or guppies—not necessarily mosquitofish—to eat the larvae. Insecticides are another, less ideal option, as they will kill beneficial insects too, but in emergencies they can be used as many are nontoxic to humans. That includes the ones being used in Brazil right now to fight Zika… and, no, they are not responsible for microcephaly. That claim has also been thoroughly disproven, despite what conspiracy theorists say.
For container breeding mosquitoes, remove the containers or drain them often. Keep an eye out for anything that can catch rainwater, from animal feeding bowls and flowerpots to old tires and plastic bags or tarps. The mosquitoes from these containers will bite you first, so you're doing yourself a favor in addition to the public health! Most importantly, protect yourself. Use insect repellents on your skin or clothes, and sleep under a bed net if you’re really deep in a disease endemic zone. Bed nets are most important for children, as they will suffer the hardest from diseases like malaria.
For more information on what you can do, find your local vector control or mosquito abatement district website or specialist and see what they recommend for your region.
For more on mosquito- and other insect-vectored diseases check the websites of the Center for Disease Control (CDC - Malaria, Zika Virus | CDC), or the US National Institute of Allergy and Infectious Diseases (Malaria, Zika Virus).
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