Mosquitoes And The Ecosystem: Do We Really Need Mosquitoes?

Stephanie L. Richards, PhD, Medical Entomologist

BRIEF HISTORY OF MOSQUITOES

Mosquitoes are thought to have been around for millions of years and will likely continue to flourish. The oldest mosquito ever found was preserved in Burmese amber 90–100 million years ago. In recent years, a 46 million–year-old blood-fed mosquito was found preserved in shale in Montana, bringing to mind thoughts of Jurassic Park.

There are over 3,500 species of mosquitoes globally, and most must blood feed to propagate eggs. However, not all of them can transmit pathogens that make us sick. In some mosquito species, when blood meal hosts are scarce, the female mosquito can produce eggs by using her own nutritional reserves, rather than blood. This is called “autogeny.”

Male mosquitoes feed only on plant nectar and female mosquitoes also feed on plant nectar between blood meals; hence, mosquitoes can play a pollinator role for some plants, although there are few published studies documenting the impact of mosquitoes on pollination.

Blood feeding adult female mosquitoes are considered pests, and many species are involved in spreading pathogens (e.g., dengue virus, malaria protozoan, West Nile virus, Zika virus) that threaten public and veterinary health worldwide. Millions of people are impacted by mosquito-borne disease each year.

MOSQUITOES AS A FOOD SOURCE FOR OTHER ANIMALS

Immature and adult mosquitoes are a food source for other animals. Different mosquito species lay their eggs in different sources of standing water (e.g., artificial container, ditch, woodland pool, treehole). Before mosquitoes emerge as flying terrestrial adults, they are aquatic and live in environments where there is standing water.

Mosquito larvae eat organic material in the water; hence, they filter and clean the water. In permanent water sources such as ponds, mosquito larvae and pupae are eaten by other aquatic animals, such as immature dragonflies, predaceous diving beetles, small fish such as Gambusia affinis (the mosquito fish) and tadpoles. Mosquito adults are eaten by animals such as adult dragonflies, bats, birds, frogs, lizards and spiders. The animals that depend on mosquitoes for food may experience population declines if mosquitoes were to disappear.

In temporary water-holding mosquito oviposition sites (e.g., woodland pools, ditches that drain, artificial containers) that do not necessarily include predators, no known benefit is gained from the presence of mosquito larvae or pupae; however, when mosquitoes emerge as adults, other predators (mentioned above) may use mosquito adults as a food source.

THE EFFECTS OF MOSQUITO CONTROL PROGRAMS

For more than a century, humans have battled against mosquitoes in the United States. In the 1940s, dichlorodiphenyltrichloroethane (DDT) eradicated many mosquito populations in the U.S., but this insecticide was banned in the 1970s due to non-target effects. Other insecticides have been developed with varying levels of success, and lack of consistent support for mosquito control programs in some regions has hampered control efforts. New insecticides and other innovative control measures should constantly be developed to suppress mosquito populations.

In areas where the primary Zika vectors (Aedes aegypti and Aedes albopictus) are prevalent, the removal of or constant monitoring, treating and/or dumping of water-holding artificial containers near homes would eliminate these mosquitoes. These mosquitoes can also lay eggs in natural sources that hold water in their leaves, such as tropical plants called “bromeliads,” so this type of vegetation would also need to be removed in order to suppress some container mosquitoes.

It is possible that the elimination of all mosquitoes would temporarily affect ecosystem balance, but it would likely not be too long before the balance is restored by another niche species. Of course, it is difficult to predict what would happen if mosquitoes disappeared or even if a few different mosquito species disappeared. However, mosquitoes are so widespread, it would be virtually impossible to remove them from the ecosystem completely (using insecticides) without impacting non-target organisms.

It is important that mosquito programs conduct regular surveillance of mosquitoes. Mosquito control programs trap mosquitoes and evaluate species occurrence and abundance. Based on this knowledge, programs can assess which populations/species are competent vectors of pathogens and conduct targeted control of the most dangerous populations. Programs also monitor and control nuisance mosquito species, such as salt marsh mosquitoes, that can limit our outdoor activities due to high numbers and voracious blood feeding. People should take steps to protect themselves from mosquitoes with repellant, wear clothing that is professionally treated with insecticide and/or cover exposed skin with clothing to avoid mosquito exposure.

Dr. Stephanie L. Richards is an Associate Professor of Health Education and Promotion in the Environmental Health Sciences program at East Carolina University. She received a B.S. in Biology and M.S. in Environmental Health from East Carolina University. She completed her Ph.D. in Entomology with a minor in geographic information science at North Carolina State University. She completed her post-doctoral work in Arbovirology at University of Florida, Florida Medical Entomology Laboratory.