Exterminate the bastards: Should we eradicate mosquitos?

The back garden is wild right now. Sunflowers, sages, primroses, golden rods, and black eyed Susans are all in blossom. Native bee magnets like mountain mint, eupatorium, and clover are drawing in droves of insects and birds. I could sit and watch the drama all day. But when I actually go outside, a hoard of menacing vampires await. Amongst the fairy land of flora exuberance lurk swarms of blood sucking mosquitos.

While it is dreadfully annoying to get covered in itchy bites, it is also increasingly dangerous to get riddled by mosquitos. As global warming increases the range of mosquitos, so too does the range of mosquito borne diseases increase. In the US, in 2019, there were 1936 cases of malaria, 1444 cases of Dengue, 974 cases of West Nile disease and 192 cases of Chikungunya. Of course, this pales in comparison to the global count of 200 million cases of malaria and about 600,000 malaria deaths every year. Mosquitos are more deadly to humans than any other animal, even other humans.

In the early 1900s malaria was endemic over 1/2 the world’s land surface. But through the use of insecticides and reduction in mosquito breeding sites, the land area infested with malaria has shrunk to just 27% of the land surface. It may be that the only way to shrink that area to 0% would be to eliminate mosquitos, as malaria vaccines and targeting the parasite in mosquitos that transmit the disease have proven problematic. But is it a good idea to eradicate a species? My intuition, and my 20 years of experience in modeling ecosystems, lead me to think this is an atrocious idea. We can not know the full consequences of eliminating a species. In the first instance, mosquitos are a major food for many bird and bat species, and mosquito larva feed many kinds of fish, dragonflies and even some diving beetles. We don’t know if removing this food source would disrupt food chains. The mosquito fish would almost certainly go extinct. Grazing patterns, and consequent ecological impacts, of caribou, horses, and cattle would change if mosquitos were gone, as much as it would no doubt please the four legged. Pitcher plants would probably go extinct for they rely on mosquito larva to break down captured insects into plant digestible chunks. Given the cocktail of stress many of the world’s ecosystems already endure - including habitat loss, pollution, ecosystem isolation, climate change, harvesting, and invasive species - it might be best to avoid piling on the further stress of eliminating the mosquito part from the ecological web.

Aside form the ecological issues from the eradication of a species, there are other issues to consider. Whether we like them or not, mosquitos contribute to biodiversity representing at least 99 million years of evolution, with all the genetic diversity, potential, and cross-species interactions that go along with that. Is it moral to wipe them out? Various philosophers suggest that a species’ status should be based on its cognition, self-awareness or social complexity. Others argue that all species have value based on their long evolutionary heritage and potential. As a self-acknowledged bleeding heart, I veer even further and shudder at the idea of destroying another species, long heritage or not.

We have intentionally eradicated other species and that didn’t give me any pause. In particular, we eliminated the two species of small pox virus in the 1970s. If we could eradicate malaria, and used the annual malaria budget of $4 billion on, for instance, regrowing rain forests or poverty reduction, would that be morally acceptable?

Another point in favor of eradicating mosquitos, is malaria control schemes don’t propose to extinguish ALL mosquitos. Only a few species of mosquitos transmit malaria out of over 3500 mosquito species. For instance, in Africa, where 95% of all malaria cases and deaths occur, only three species of mosquito transmit malaria: Anopheles gambiae, Anopheles coluzzii and Anopheles arabiensis.. Incidentely, the meaning of the greek work “anopheles” is useless. Perhaps a few useless mosquito species wouldn’t be missed?

While you may be thinking that wiping out an entire mosquito species is purely speculative, it is well within humanity’s reach. The Bill & Melinda Gates Foundation believes they are very close to being able to wipe out Anopheles gambiae. Using a gene-splicing technique, CRISPR-Cas9, scientists have found and edited the gene determining the size of Anopheles gambia’s proboscis. The scientists can thus breed female mosquitos that have smaller, male sized stingers. The modified female mosquitos can’t suck blood from mammals and thus can not produce healthy mosquito eggs. In laboratory trials, modified Anopeles gambia populations died out in 7-11 generations. The Bill and Melinda Gates Foundation expects to have regulatory approval for this technique in 2024, and expects to start releasing the modified mosquitos in 2026.

There are other mosquito modifications projects underway. One involves sterilizing male mosquitos with radiation. Test studies found that nearly all wild Aedes albopictus, the Asian tiger mosquito, died following a massive release of sterilized males. Another genetic manipulation study, that results in female offspring of Aedes aegypti dying before they can bred, has been carried in Florida. Results have been positive and the EPA has approved further tests of this technique in the hopes of reducing the transmission of Zika and dengue fever.

In addition to the worries about ecological and moral consequences of species eradication, gene editing presents the concern that the gene modifications might spread into non-target species. And furthermore, previous attempts at gene editing have had unexpected consequences. Perhaps most famous of these is the highly controversial case of the Chinese twins whose genes were tinkered with prior to their birth. The goal of this gene editing experiment was to prevent the twins from being susceptible to HIV. However it seems that the twins are also now less likely to live to the age of 76.

Given the massive benefits of that would arise from eliminating malaria, but the minefield in mosquito elimination techniques, how do we choose which, if any, of these mosquito reduction techniques should be used? The World Health Organization, among others, suggests that transparency and community input are vital for these kinds of morally complicated decisions.

And what about at home? How can we responsibly act to reduce mosquitos in the places we manage? First of all, it’s helpful to know a few relevant things about the habits and lifecycle of mosquitos. Mosquitos don’t bite us for food, they primarily eat nectar. However, mosquito eggs need protein which the female mosquito provides by drawing blood. She is attracted to us by the carbon dioxide in our exhalations and by our skin odors. A female mosquito will usually lay her eggs in water. But not always, the eggs can survive for months in dry conditions. Once an egg is exposed to water, the larval form emerges. Bizarrely enough, these so called wrigglers molt four times until they turn into the pupal mosquito form, which is also a water dweller. Eventually, the pupa metamorphoses, much like a butterfly, into a flying mosquito. And the cycle starts over again.

A common method to break this cycle is to reduce the available habitat for the larval and pupal stages - in other words get rid of standing water. From first contact between water and egg to adult-flying-mosquito takes anywhere from 4 days to 4 months, depending on temperature and mosquito species. Therefore, if we empty out all standing water in pots, tarps, bird baths and so forth every 4 days, many mosquito larva and pupae in our area will be eliminated. And thus many adult flying vampires will be gone too. We can also turn the standing water requirement of the mosquito lifecycle to our advantage - by setting a trap for egg laying females. By simply setting out a bucket of water, and dumping it out every four days, we’re likely to kill some larva. But we’ll catch many more if the trap water smells like a mammal breathing out, i.e. if the trap is releasing carbon dioxide. This is easy enough - just add some fresh green plant material like grass clippings or green leaves for as they decompose they release carbon dioxide. Finally, if you don’t think you will empty your buckets every 4 days or so, you can add mosquito dunks. These kill mosquito larva and are apparently harmless to other life.

Killing the larval form of mosquitos will take a few days to reduce the biters around your place. If you want an more immediate result, you can try to catch the flying adult forms. Again, using the lure of carbon dioxide, you can build funnel type traps that the mosquitos can’t escape. Or you can place a net over a fan near a carbon dioxide source (such as a bucket with grass and water), then female mosquitos seeking our blood will get sucked into the fan and be trapped in the net.

Our next line of defense is mosquito repellents. These usually work by masking our smells so mosquitos don’t find us. In addition to being attracted to our exhalations of carbon dioxide, mosquitoes are also attracted to our skin odors and heat. Mosquitos are VERY good at smelling us and can detect the presence of a human at up to 100 feet away. In fact, unlike most other animals, mosquitos have at least two different receptors that trigger their “food over there” neurons. How do they fit all that in such a tiny brain?

The most widely used mosquitos repellent is DEET, or C12H17NO for the chemically inclined. While the Registration Review Program of the EPA has found that DEET poses no risks to human health, non-target species, nor the the environment, the EPA still recommends that you wash off DEET with soap and water. Hmm, I wonder why? It’s probably because there have been a handful of deaths connected with DEET, DEET has been implicated in Gulf War Syndrome, and DEET has been shown to affect human’s cardiovascular and nervous systems before it is completely metabolized by the body. Note, however, that these impacts are rare. And they seem to only arise when people apply combinations of skin creams and DEET or when DEET is used frequently over long periods. It is worth noting that many health agencies advise against applying DEET at the same time as sunscreen or any other lotion.

The situation with regard to DEET’s environmental effects is similar - no big red flags but a few warning signs. We know it does not bioaccumulate, like mercury, accumulating up the food chain. And DEET brakes down relatively quickly in nature. But even at low concentrations, DEET is known to be toxic to fish and aquatic invertebrates and it is often detected in waste water.

All summed, DEET appears to be very mildly poisonous, but can prevent the spread of disease. For my own self, where mosquito borne diseases are very rare, I will avoid DEET and continue to use natural scents to throw off mosquitos. Lemon eucalyptus spray is very effective at keeping the bastards at bay and it even offers longer lasting protection than DEET.

Finally, spraying with pesticides is a common approach to controlling mosquito numbers. I’m sure you can guess that what I think about that. Most residential companies like Mosquito Joe, Mosquito Squad and Mosquito Authority in the US use pyrethrins or pyrethroids, derivatives of chrysanthemum flowers, in their sprays. Pyrethrins and pyrethroids are toxic to a wide variety of insects. And somewhat disturbingly, they act by interfering with the nervous system of insects such that they become disoriented, develop tremors and concussions, and eventually die. Contrary to claims by these residential services, these sprays also kill butterflies, ladybugs, dragonflies and many other beneficial insects. Spraying with pyrethrins and pyrethroids has almost certainly contributed to the decrease in bee populations documented around the world and the loss of 30% of North American birds in last few decades. And as these pesticides wash off the sprayed plants and flow down stream, they enter our rivers and streams. Most aquatic invertebrates and fish are highly susceptible to these insecticides leading to repetitive neuron firing and paralysis and death.

So our arsenal of eco-friendly at home mosquito control includes reducing standing water on our property, setting up traps, wearing loose fitting lightly colored clothes, and spraying ourselves with lemon-eucalyptus to mask our smell. That’s all I have for you today dear readers, I’ve got to go scratch my mosquito bites.