Mosquitoes can have both positive and negative impacts on the ecosystem. As part of their useful role, the larvae of mosquitoes live in water and provide food for fish and other wildlife, including larger larvae of other species such as dragonflies. The larvae themselves eat microscopic organic matter in the water, helping to recycle it. Adult mosquitoes make up part of the diet of some insect-eating animals, such as birds, bats, adult dragonflies and spiders. They also help pollinate some flowers, when they consume nectar.
But mosquitoes also can have a damaging role, harming other animals by being a vector for diseases, such as malaria, yellow fever, encephalitis and dengue. The mosquitoes don't cause the diseases themselves, but only act as carriers. They need to feed on a person or animal who is already infected, then when they bite a healthy person or animal afterwards, they pass on the disease.
In places where a particular disease is not already present, there's no risk of catching it from mosquitoes, but ecologists worry, because if infected humans or animals do come into the area, the mosquitoes that already live there will spread the disease among the rest of the healthy population.
Usually the bites themselves are just an annoyance if there's no chance of illness, but sometimes mosquitoes are so overwhelming, their sheer numbers have a major impact. In some places around the Arctic where summers are short, mosquito season is brief, but so many are competing for a bite of mammal blood that they cluster in dense swarms, causing caribou herds to flee.
As annoying and dangerous as mosquitoes are, scientists don't want to recommend exerminating all of them, or any other species, unless they're sure there won't be any unintended bad consequences. Thirty years ago, people understood that eradicating one species might affect others, but they looked more for large, obvious changes. Today, scientists examine the ecosystem more closely, since even small changes can produce large alterations over time. Bugs, in general, have a long history of both helping and hurting human life, and interacting with people and the ecosystem in ways one might not expect. A humorous, scientifically accurate book about them, by a professor of entomology is Bugs in the System: Insects And Their Impact On Human Affairs.
The problem with getting rid of all mosquitoes is that we don't know everything about them yet. They may be useful in ways we can't imagine. John Carlson, studying at Tulane University, wrote, about Costa Rica, "If all of the mosquitoes were killed, the ecosystem would probably not suffer, unless the poisons used to kill them also killed organisms that are required for the balance of the rainforests."
But he cautioned that we also can't be sure that some useful chemical might one day be found in mosquitoes, so they may have some value in the future that we're not even aware of now.
Still, many scientists think the world would survive the loss of mosquitoes without too much damage. The problems may be caused more by how we get rid of them.
Even if mosquitoes themselves don't have a vital role in a particular ecosystem, insecticides used to kill them may harm other creatures that do. A Florida mosquito control white paper points out that some small organisms, such as arthropods the same size as mosquito larvae, may be more vulnerable to pesticides than the mosquitoes themselves. Trying to kill off the mosquitoes may kill off all similar creatures. Fish and other animals which ate mosquito larvae wouldn't be able to switch to another diet, because not enough similar creatures would survive. So scientists not only need to learn the role of mosquitoes in the ecosystem and judge how important they are, they also need to study the role of any other creatures that might be affected by our attempts to get rid of them.
A possible way of eradicating them without killing any other living things, is a new plan scientists are working on, to release males with a lethal gene which prevents their offspring from surviving.
One company has made a mosquito which won't live unless it receives the antibiotic tetracycline, according to an article in the Oct. 30, 2011 New York Times. The company can breed the mosquitoes in a lab by giving them the antibiotic to keep them alive, then introduce them in the wild, where they will live long enough to mate with normal females, but their offspring will die. The company released 19,000 of the special mosquitoes in 2009 on a Grand Cayman island, and the males with the lethal gene successfully reduced the mosquito population, though they still weren't as successful at breeding as normal males, so many of the next generation were normal and survived.
Unlike other insecticides, this way of controlling them can only affect mosquitoes, but there are still ethical concerns.
Though scientists are fairly sure that mosquitoes' useful role in the ecosystem is small enough that other insects could take over, if we ever have the ability to eliminate them completely we'll want to be sure they're not serving some purpose we're currently unaware of.
Images courtesy of the USDA.