Girl sprays mosquitos with bug repellent

The mosquito has its day … from annoying pest to valuable resource

Mosquitoes—Spanish for “little fly”—are an important part of the world’s ecosystem. While most would prefer to not suffer its bites, the value of one of nature’s most annoying—and also sometimes dangerous—flying pests can’t be understated.

Twelve of the more than 200 types of mosquitoes in the United States spread germs that can make people sick. The most common is West Nile virus, but their bites are also responsible for outbreaks of Zika virus, yellow fever and malaria. But while there are dangers posed by mosquitoes, they also play a valuable role in nature. 

In recognition of World Mosquito Day (Aug. 20), The Daily asked Michael Benard, associate professor and chair of Case Western Reserve University’s Department of Biology, about the insect and how researchers are attempting to control mosquito populations while maintaining environmental stability. 

Benard’s research is intended to determine how changing environments affect organisms’ abundances, traits and ecological interactions, with a focus on amphibians and why the species is in a worldwide decline.

“Amphibians provide an important ecological service in insect control and are a sensitive indicator of environmental change that might directly harm humans,” he said. 

Benard explained more about the role of mosquitoes and their positive impact on the world’s ecosystem.

Why are mosquitoes important? 

There are more than 3,500 species of mosquito worldwide, and they can be an important food source for animals. For example, mosquitoes appear in the diets of over 70% of the little brown bats sampled in the midwestern U.S., and the aquatic larvae of mosquitoes are a favored prey for many salamanders. Individual salamanders can consume over 800 mosquito larvae per day, so if mosquitoes disappear, many animals will lose an important food source. 

How do our attempts to control them, mostly through sprayed poisons, affect the balance of nature?

Small standing bodies of water, such as bird baths and water sitting in old tires, can produce large numbers of mosquitoes, so control recommendations include removing these sources.

A variety of insecticides can be used to control both the flying adult mosquitos and the aquatic larval mosquitoes. However, some insecticides may have negative effects on fish, amphibians and other animals, depending on the concentrations. Other compounds are more specific. Experimental studies show that Bti (Bacillus thuringiensis)—which is derived from a soil bacteria—kills mosquito larvae and is much less toxic to non-target species than other insecticides.

Biological controls can also be used to control mosquito populations. Mosquitofish eat mosquito larvae and are frequently released in some areas to control mosquito populations which avoids the toxicity of some insecticides. But they will also eat animals other than mosquito larvae, such as other aquatic insects and amphibian larvae which can lead to the decline of native species. 

A targeted approach that uses multiple methods based on the local environment can be an effective way to control mosquitos while limiting negative effects on other species. 

What other things can the science community do to find the balance between control and conservation?

There are many examples of how maintaining healthy, intact ecosystems has many benefits for people. Citing amphibians and mosquitos as an example, biologists in Switzerland surveyed wetlands across many different habitats and found mosquitos were much more abundant where humans had modified the wetlands. In particular, mosquitos were more abundant when amphibians were rare. 

A key message of many of these studies is that protecting the environment has many benefits that are important to human wellbeing, but they are often hard to detect if you aren’t looking for them.