By Orion McCarthy 

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No one likes the sound of a mosquito buzzing in their ear.

Aside from being a bloodsucking pest and ubiquitous nuisance, mosquitoes are the deadliest creatures on the planet. The tiny insects are responsible for an estimated 725,000 human deaths each year through the transmission of diseases such as malaria, dengue, yellow fever, West Nile and now, the Zika virus.

The average number of human deaths per year attributed to each animal is listed above. The mosquito, by far the deadliest animal on the planet, is responsible for an estimated 725,000 human deaths annually. Mosquitoes are even more dangerous than other people: each year they cause more deaths than all annual homicides, suicides, manslaughter and war related deaths combined. Data: Bill and Melinda Gates Foundation.

Humanity’s well-deserved hatred for the bloodsucking insects has inspired dreams of complete mosquito eradication. Yet ridding the world of mosquitoes would be no easy feat.

At the peak of their breeding season, mosquitoes outnumber every other animal on the planet except for termites and ants. They are also highly adaptable, and are found across a diverse range of environments on every continent except Antarctica.

Mosquitoes are largely controlled today using chemicals such as DDT and DEET. While these chemicals are effective for localized mosquito reduction, they are inefficient and impractical for controlling mosquitoes over large areas. Both chemicals are also known to hold environmental and human health risks.

However, new advances in synthetic biology are sparking a mosquito control revolution. Researchers are pursuing genetic modification and gene drives as a means of controlling, and in some cases, entirely eliminating mosquito populations. While many experiments are still in testing, some researchers predict that such technology could be used to wipe mosquitoes from the planet in a matter of years.

But don’t throw out your bug spray just yet.

Just because we could eradicate all mosquitoes doesn’t necessarily mean we should.

Before humanity attempts such a task, some questions should be asked: Are there any ecological reasons for keeping these pests around? Do they serve a purpose? What would happen if all mosquitoes disappeared tomorrow?

In short, why shouldn’t we kill every last buzzing, annoying, bloodsucking mosquito?

1. Other animals eat them

Lots of animals eat mosquitoes and mosquito larva, including geckos (top left), swallows (right), and the aptly named mosquito fish (bottom left). Photo credit: Qasem Elakhdar, Paul Bannick, and the University of California.

Like all other insects, mosquitoes are part of the food chain.  While no animals are known to subsist solely on mosquitoes, they are a valuable protein source for bats, birds, dragonflies, spiders, and even other mosquitoes. Fish, turtles, and frogs also eat mosquito larvae. Studies have shown that mosquitoes are an important food source for migratory birds, which flock to the Arctic each summer to feast on thick clouds of mosquitoes that blanket the polar skies. Without mosquitoes, the future of arctic migrations among some bird species would be uncertain.

2. Most species are harmless to humans

Aedes ablopictus, also known as the Asian Tiger Mosquito, is one of the few mosquito species that transmits diseases to humans out of 3,500 mosquito species worldwide. A nonspecific campaign to eradicate all mosquitoes would obliterate a significant source of biodiversity. Photo credit: Wikipedia.

There are an estimated 3,500 species of mosquito worldwide, compared to the 5,416 known species of mammals. The high level of mosquito biodiversity stems from their range of hosts. Each mosquito species occupies a specialized niche, targeting a different species of bird, reptile, amphibian, mammal, or even fish. Some mosquito species are generalists and prey on multiple different types of animals.

Among the mosquito species that do target humans, just two dozen species are responsible for virtually all mosquito borne infectious diseases. These species belong to the genera Culex, Anopheles, and Aedes, and include the invasive Asian Tiger mosquito (Aedes albopictus), the common malaria mosquito (Anopheles gambiae), and the current vector species for the Zika virus (Aedes aegypti). Targeted control efforts aimed at these species would be far more effective than wholesale eradication of all mosquitoes.

3. They are pollinators

Mosquitoes pollinate flowers, just like bees and butterflies. Photo credit: Howard Cheek & NWF.

Only female mosquitoes suck blood, and they only do so when they are brooding a clutch of eggs. The rest of the time, female mosquitoes join their male counterparts alongside flowers, feeding off the nectar within. Just like beetles, bees, and butterflies, mosquitoes are pollinators, inadvertently spreading pollen as they travel. However, many other insects are pollinators as well, and there is a debate amongst ecologists as to whether plant species would suffer in the absence of mosquitoes, or if other pollinators would pick up the slack.

4. They protect the rainforest

Photo credit: Kuvaton.com.

As crazy as it sounds, the presence of mosquitoes can actually help to conserve valuable habitats for other animals. Bites from malaria-laden mosquitoes are a powerful deterrent to human colonization in remote rainforest regions across the tropics. In this way, mosquitoes play the unwitting role of ecological vanguard by making some environments uninhabitable to humans. The ecological role of poison ivy is similar; by deterring humans and mammalian herbivores, the poisonous plant helps degraded forest patches recover from disturbances.

5. We don’t know what will happen when they’re gone

A swarm of mosquitoes in the arctic. Photo credit: Mother Nature Network.

While the ecological role of mosquitoes is well studied, no one can be sure what cascading ecological effects might result from mosquito removal. Unseen environmental or humanitarian consequences, such as the extinction of species unknown to rely on mosquitoes or the emergence of a deadly new disease vector in place of mosquitoes, can’t be ruled out.  As the saying goes, the devil you know is better than the devil you don’t.

Balancing Ecology and Public Health

The Zika virus is thought to cause microcephaly in newborns, a neurodevelopmental disorder characterized by a small head and stunted mental development. More than 4 million people could become infected with Zika by the end of the year. Photo credit: CDC.

For many people, especially those in areas affecting by malaria, dengue, and Zika, the ecological benefits of mosquitoes don’t outweigh the cons of possible infection.

Of course, such sentiment is more than understandable. But does the choice between a healthy environment and a healthy humanity have to be so black and white? Is it possible to keep the ecological benefits of mosquitoes while eliminating the transmission of mosquito-borne infectious diseases?

If scientists have their way, the answer is yes.

While some geneticists fiddle with gene drives in a quest to wipe out mosquitoes entirely, others have set their sites on a more humble goal: reducing populations of the most virulent mosquito species below the threshold for disease transmission.

The technique, pioneered by the British company Oxitec, relies on inserting a self-destruct gene into laboratory reared male A. aegypti mosquitoes, the type that would normally carry the Zika virus. Instead of spreading Zika, the males pass on their modified genome to their offspring. The gene releases a protein that halts larval development, killing the next generation of mosquitoes.

Since the offspring die before reproducing, their modified gene can’t be passed on into the larger mosquito gene pool unless public health officials release more modified males. This keeps the genetically modified genes in check and keeps the entire population from going extinct.

The effectiveness of Oxitec’s self destruct gene is currently being tested in South America. Preliminary trials have shown tentative success, and the modified mosquitoes may be used to decimate populations of their Zika spreading relatives on a large scale in the near future.

High magnification image of Aedes aegypti cells with Wolbachia (green) – Photo credit: Eliminate Dengue.

Australian scientists have also tried to tackle the mosquito problem by developing a natural form of mosquito birth control. They discovered that A. aegypti mosquitoes infected with a bacteria called Wolbachia, which naturally occurs in 60% of all insect species, can only reproduce with other mosquitoes carrying the exact same strain of the bacterium. By raising male mosquitoes with different Wolbachia strains in the laboratory and releasing them into the wild, researchers hope to decrease the chances of successful reproduction among the target mosquito species, suppress their population, and reduce disease transmission.

Of course, releasing genetically modified organisms into the environment is fraught with risks. However, given the current humanitarian crisis, the harmful ecological effects of pesticides, and the goal of containing rather than eliminating target mosquito species, these engineered mosquitoes offer the best bet for a healthier humanity while minimizing environmental damage.

Do you think the ecological benefits are worth keeping mosquitoes around, or would you like to see them gone all together?  Argue your case in the comments below!

And above all, make sure you take simple steps to stay safe this mosquito season!

LEARN MORE

• How to Reduce Mosquito Populations Without Pesticides (Hint: Get rid of Standing Water!)
• Mosquito Facts – 33 Things You Didn’t Know About Mosquitoes
• 5 Things the CDC Wants You to Know About the Zika Virus
• Learn How the Bill and Melinda Gates Foundation is Working to Fight Malaria

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