ELi ON EARTH: Female Mosquitoes Bite East Lansing Residents

Above: The author being bitten by a local mosquito.

More than nine inches of rain in June and continued rain well into July have created mosquito development habitat in the standing water of yards, fields, and nearly any upright container in town. The mosquitoes that hatch in the summer can turn over a new generation every two weeks as long as there is standing water for their reproduction cycle, and that means we in East Lansing have at least a few more mosquito-filled weeks left in the season.

Mosquitos are a kind of fly and have a four-stage life cycle: egg, larva, pupa, and adult.  We all know the adult females well; they are the ones that bite people. In many mosquito species, the adult females bite an animal to obtain a blood meal that provides protein for egg production. But not all mosquitoes bite animals; some mosquitos “bite” plants and do not bite animals at all. Just to complete a complicated picture, there are local mosquitoes that may feed off plants between blood meals or may not even need a blood meal to lay their first batch of eggs.

Each species of mosquito has its own pattern of egg-laying.  Some species prefer water trapped in natural crevices of plants, others prefer larger bodies of quiet or stagnant water, and some species deposit their eggs in a damp area where the next flood triggers their eggs to hatch.

Mosquito larvae and pupae are the aquatic stages of mosquito development, although both larvae and pupae must surface in order to breath.  The larvae move their whole bodies to swim and are called wigglers.  Here is a photo of a wiggler in the author’s neighborhood.

Wigglers swim to find algae and bacteria to eat before returning to the surface to breath through the eighth segment of their body or a siphon on their back end.  This video shows mosquito larvae swimming in the author’s neighborhood.

Both the larvae and the pupae of mosquitoes stick to the water surface using the surface tension of water.  A very thin layer of oil on the surface of the water significantly decreases the surface tension of water, making it impossible for the larva and pupa of the mosquito to stay on the surface to breath. Without the surface tension of water, the larvae and pupae of mosquitoes, and other flies, will drown.

Mosquito larvae metamorphasize into pupae, which can swim by bending their abdomen, but they do not eat. Pupae use surface tension to suspend themselves from the surface of water via a respiratory trumpet. The pupal stage lasts a few days while the metamorphosis process culminates with the hatch of the adult mosquito.

The adult males feed on nectar and other plant liquids and try to find mates. Their adult lives last generally only a few days and don’t involve East Lansing’s human residents. The female mosquitos will bite local animals including some insects (caterpillars), birds, reptiles, and mammals.

Mosquitos find their blood meal through a range of chemical receptors and their vision. Clearly, mosquitos like some people more than others based on chemicals in their sweat and breath.  There is good evidence that mosquitos are drawn to the carbon dioxide in our breath, and so people who exhale more are more likely to attract mosquitos.  There seems to be controversy about a variety of other possible mosquito attractors like color, foods, pregnancy, blood type, beer drinking, etc.

Once on the skin of their victims, mosquitos bite using their mouth parts, which contain the same parts as other flies but elongated into a proboscis. As the mosquito bites its victim, it injects some of its saliva to keep the blood of the East Lansing resident from clotting in the mosquito’s proboscis. The proteins in the saliva cause a histamine release in the skin of victim, resulting in a red, itchy, swollen area around the bite, called a wheel. This photo shows a wheel from a mosquito bite on the author, who is a frequent victim of mosquitos.

The saliva mosquitoes inject into victims can also carry disease.  The State of Michigan tests mosquitos for a variety of viruses, including West Nile Virus, which can infect a variety of animals including people, horses, and birds.  Mosquitos are also the vectors for Yellow Fever, Dengue Fever, and the parasite that causes malaria, Plasmodium, which causes as much morbidity and mortality as any human disease on earth. Michigan has the mosquito species that can carry all of these illness, but aggressive anti-mosquito programs in the last century largely eradicated the most serious of these disease.

Controlling mosquitos is best done by disposing of the stagnant water they use for their development cycle. Mosquitos can complete their development in water trapped in an empty can, a wheelbarrow, or the base of the flowerpot. Draining stagnant water or covering it with a thin layer of vegetable oil is simple method to control mosquito habitat.

Although there are animals that eat mosquitoes, there are no animals that can control populations enough to change the human-mosquito experience. Some birds and bats eat mosquitoes, but there is so little food-value in a mosquito that those animals focus on larger insects for their meals. Mosquito repellents that use DEET are generally safe for humans and do repel mosquitos. Loose clothing, insect repellents, and staying in during dawn and dusk are good methods of avoiding mosquito bites. Humans have a variety of other defenses including hair and their hands. Below is a mosquito trapped in the hair of the author.

Most insecticides that effectively kill adult mosquitos also kill beneficial insects and some are dangerous to people. The state recommends that pesticides only be used as part of an integrated mosquito control program that considers risks to human health and the environment.