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Are mosquitoes any good?

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Mosquitoes are at best annoying, and at worst deadly.

If you look up a list of the world's most hated animals, you're probably going to find mosquitoes on that list, and with good reason.

Here in the United States, mosquitoes are mostly just an annoying nuisance with the occasional warning about West Nile or some other mosquito-borne disease. But each year, 1 in 12 people worldwide are infected with a mosquito-borne illness, and about every 45 seconds, someone dies from malaria, a parasite transmitted by mosquitoes1.

So do mosquitoes have any redeeming qualities? What stops us from completely eradicating them from off the face of the earth? What good are mosquitoes?

Mosquitoes have been around since the time of the dinosaurs, and they really started to diversify as plants developed flowers2. Mosquitoes are nectar feeders, the females only need a blood meal to lay eggs. And since mosquitoes are visiting flowers, they are actually pollinators. I don't have a measure of how much pollinating they do, but in a world where pollinators are on the decline, every little bit helps.

Mosquitoes and their larvae are also important food sources. Their larvae live in water and are eaten by other aquatic insects and fish. Now there are exceptions - some mosquitoes lay their eggs in temporary bodies of water such as a watering can left out in the rain. Those larvae don't serve as food for other aquatic animals, but as adults they can be preyed upon by animals such as dragonflies or bats.

Mosquitoes are also inspiring technological innovations. A mosquito's needle-like mouth is inspiring new devices for performing biopsies3 or for less painful injections4. Mosquito aerodynamics are being investigated as a way to help drones and helicopters avoid crashes5. And they're also being used to help administer vaccines.

Using mosquitoes to deliver vaccines actually starts with sandflies. Sandflies, like mosquitoes, are a type of fly, suck blood, and transmit disease, one of these being leishmaniasis. Leishmaniasis causes between 20k-30k deaths per year6, so not nearly as much as malaria but still not a small number. What's interesting about leishmaniasis is that infection is enhanced by the presence of sandfly saliva7. In fact, instead of creating a vaccine against leishmaniasis directly, sandfly saliva itself could serve as a vaccine target.

To test how effective this vaccine would be, scientists needed to expose mice to one of the salivary proteins to measure how well that would protect against leishmaniasis. The simplest way would be to raise sandflies in the lab and have them bite the mice, but at least at the time, the sandfly larval stage was still a bit mysterious8. An alternative would be to clone the gene into bacteria or yeast and purify it out, the same process used to produce insulin. However, some researchers in Japan had a different idea.

The mosquitoes that transmit disease are very well studied and can be raised in a lab. We also know how to genetically modify them. What these researchers did was they took a gene for the component of sandfly saliva that helps leishmaniasis and put it into the mosquitoes' DNA9 10. These mosquitoes were now producing this component in their own saliva. They raised a bunch of these genetically modified mosquitoes and had them bite the mice. Now I can't say if it was any easier inserting this gene into mosquitoes vs isolating it from bacteria or yeast, but it is certainly a cool, if frightening, idea. The researchers were able to show that the mice did indeed produce antibodies against the saliva protein. That doesn't mean we have a new treatment for leishmaniasis, but it does provide more evidence that we are on the right track when it comes to safely vaccinating against leishmaniasis and it also demonstrates the feasibility of using mosquitoes to administer vaccines.

Now before you get worried about mosquitoes secretly delivering vaccines, there were a few issues with this approach, the main one being that each mouse needed to be bit hundreds of times by the genetically modified mosquitoes. Now imagine a person - you would need to be bit thousands if not tens of thousands of times for a mosquito-borne vaccine to be effective. So if takes that many mosquito bites to deliver the vaccine, how is this even useful?

Malaria is a huge problem in many parts of the world. We have medicine for malaria, but there are drug resistant strains of malaria out there11. As of just recently we do have some malaria vaccines with several more in clinical trials, but malaria has a more complex lifecycle compared to viruses or bacteria, so it's a bit trickier to create an effective vaccine and by no means mission accomplished just yet.

One vaccine candidate uses live malaria parasites that have been genetically modified to not cause sickness. Rather than work with infected blood or isolate the parasites from mosquito saliva12, researchers are bypassing the middleman so to speak and having the infected mosquitos bite the clinical trial participants13. This keeps costs down and lets researchers gather data on the effectiveness of this approach before moving on to more costly production techniques for an actual injectable vaccine. Mosquitoes are now being used as tools to develop vaccines against the very infections they transmit.

So mosquitoes might be good for something after all, but is it enough to redeem them? Maybe we should just get rid of them still.

Let's start broad and say we want to get rid of all 3600 species of mosquito in the entire world. Should we do it? What would be the consequences of doing that? We can't really say.

Mosquitoes, in general, aren't super well studied. Now the disease carrying mosquitoes are very well studied, but those comprise fewer than 2002 of the 3600 mosquito species out there. If I do a Google Scholar search for Aedes, the mosquito genus that can transmit things like Zika, I get over half a million results. If I instead search for Lutzia, a group of mosquitoes whose larvae coincidentally prey upon the larvae of Aedes mosquitoes, I get fewer than 2,000 results. These results are probably skewed by papers that mention the genus Aedes but don't actually study them directly, but even if I take a look at an insect focused journal and account for how many species are in each genus, there are still more papers published about the genus Aedes than about the genus Lutzia. (Journal of insect science: 416 for aedes (190 species) 1 for Lutzia (8 species)). Now I'm not saying we need to equally study all mosquitoes; Aedes mosquitoes are much more relevant to human health than Lutzia. What I am saying is we simply don't know enough to be able to predict what would happen to the world's ecosystems if we were to get rid of all the mosquitoes14.

What if we get a little more specific and only eradicate the species that carry disease - we'll only get rid of those 100-200 species that transmit disease and leave the other 3500 or so alone. That should be okay, right? Maybe at first.

Aedes aegypti, the yellow fever mosquito, is a disease carrying mosquito - it can transmit Zika, dengue, chikungunya, and of course, yellow fever. Culex pipiens, also known as the common house mosquito, can carry West Nile Virus. If Aedes aegypti is present in an area, Culex pipiens cannot thrive as well as it could otherwise15. The yellow fever mosquito displaces the common house mosquito. Now both of these mosquitos can carry disease so either way they're a problem for us, but what it does demonstrate is that the presence of a mosquito can, not necessarily always but can, prevent another species from occupying the same habitat. If we were to get rid of all the disease carrying mosquitoes, other mosquito species would most likely come in and take over their habitats. So what's the problem with that? The pathogens we are trying to avoid might be able to make the jump to these newcomers. Maybe they can already be transmitted by them (because remember, we haven't extensively studied all mosquito species), or maybe those pathogens can evolve to be transmitted by the newcomers, or maybe there'll be some new disease that mosquitoes can start transmitting. This becomes a game of whack-a-mole - we might be fine completely eradicating all the disease carrying mosquitoes, or even just a handful of them, but we also might end up right back where we started.

Where does that leave us? What entomologists typically recommend is local population reduction of disease carrying mosquitoes. We don't need to kill all the mosquitoes in the whole world or wipe out entire species; we just need to control the mosquito populations occupying the same areas as humans.

So are mosquitoes any good? Do they really deserve to be on our lists of the most hated animals? Mosquitoes do indeed play a role in the ecosystem, however small or large it may be, and they are inspiring new designs in engineering and medicine. But you also can't deny the fact that they've been complicit in the deaths of millions of people. So while I do think mosquitoes have some value, maybe they do deserve to remain on our lists of the most hated animals until such a time that we can reduce human suffering and coexist with these troublesome little flies.

Footnotes

  1. WHO Malaria fact sheet

  2. Phylogenetic analysis and temporal diversification of mosquitoes (Diptera: Culicidae) based on nuclear genes and morphology 2

  3. Mosquito proboscis-inspired needle insertion to reduce tissue deformation and organ displacement

  4. Realistic imitation of mosquito's proboscis: Electrochemically etched sharp and jagged needles and their cooperative inserting motion

  5. Watch this mosquito-inspired drone light up and avoid a crash

  6. Leishmaniasis

  7. Sand-Fly Saliva-Leishmania-Man: The Trigger Trio

  8. Breeding Sites of Phlebotomus sergenti, the Sand Fly Vector of Cutaneous Leishmaniasis in the Judean Desert

  9. Researchers Turn Mosquitoes Into Flying Vaccinators

  10. Flying vaccinator; a transgenic mosquito delivers a Leishmania vaccine via blood feeding

  11. Drug Resistance in the Malaria-Endemic World

  12. Protection against malaria in mice is induced by blood stage–arresting histamine-releasing factor (HRF)–deficient parasites

  13. A box of 200 mosquitoes did the vaccinating in this malaria trial. That's not a joke!

  14. Why mosquitoes should not be eliminated

  15. Kill All the Mosquitoes?!