Did you know that the itching and raised red spot caused by a mosquito bite are actually an allergic reaction to the mosquito’s saliva? Mosquitoes are well known for their itchy bites, nearly pervasive presence, and the constant hum of their buzzing wings; yet many people are unaware that mosquitoes are vectors, or carriers, of some of humanity’s most deadly diseases.
There are approximately 3,500 species of mosquitoes grouped into 41 genera, and of these the majority of mosquito-borne diseases are transmitted primarily by only 3 genera: Aedes, Culex, and Anopheles. The Culex mosquito is a carrier, or a vector, of elephantiasis and encephalitis, as well as the West Nile virus. The Aedes mosquito is a carrier of yellow and dengue fevers and of encephalitis. As the main vector of malaria, the Anopheles mosquito is the deadliest of the three genus of mosquito. It is also capable of transmitting W. bancrofti (filarial worms), various arboviruses, onyong-nyong, tataguine, elephantiasis, equine encephalitis, as well as other viruses, but malaria is unquestionably the most threatening.
Mosquitoes are part of the Culicidae family, nematocerid (thread-horns) flies, which are a suborder of elongated flies with thin, segmented antennae and mostly aquatic larvae. Like all flies, mosquitoes go through four stages in their life cycle: the egg, larvae, pupa, and imago or adult.
The first three stages of the mosquito’s life cycle are mostly aquatic and typically last 5-14 days depending on the species and climate. Mosquitoes living in areas where freezing or drought occurs are able to spend part of their year in diapause; they are able to delay their development for months at a time and continue the life cycle when there is enough water or warmth. For example, some larvae are frozen solid in ice during the winter and complete their development during the spring melt; some eggs remain unharmed when they dry out and hatch later once they are covered with water; and other species can winter over as adults and return to flight once it warms up. Evolution at its best!
Both male and female mosquitoes gather nourishment from nectar and other plant sugars. Only some of the mosquito species are actually blood feeders; in fact, only the female mosquito has the physiology necessary for sucking blood. Female mosquitoes are attracted to body temperature, odors, movement and even exhaled carbon dioxide, which help them hone in on their next victim whether human or animal. The female has two specialized pairs of cutting stylets that slide against one another to slice through the skin at the end of the proboscis. Once the mosquito’s proboscis enters the flesh it begins probing around for a tiny blood vessel to feed from. The proboscis has two hollow tubes, one that injects saliva into the microscopic wound and one that withdraws blood. The mosquito’s saliva includes a combination of antihemostatic and anti-inflammatory enzymes that disrupt blood clotting and inhibit the pain so the victim does not notice the attack.
The female mosquito seeks out a blood meal after mating to provide protein for egg development. After digesting the blood she lays between 50-200 eggs. The mosquito habitat differs between species, thus where they lay their eggs and the way they lay their eggs, called oviposition, also differs. Some mosquitoes lay their eggs on the surface of standing water; some lay their eggs in mud; some attach their eggs to aquatic plants; and others prefer to breed in natural reservoirs on plants such as bromeliads or pitcher plants. Different species will lay their eggs individually, some lay them in groups and others form layers of eggs called “rafts” that float on the water.
The eggs hatch to become larvae, which use mouth brushes to feed. Larvae breathe through spiracles (structures similar to a siphon, located on the eighth abdomen), forcing them to swim to the surface frequently for air. Larvae spend much of their time feeding on microbes and algae near the surface of water and only dive below when disturbed. They swim either through propulsion with their mouth brushes, or by jerky body movements, giving them the nickname “wigglers.”
The larva grows into the pupa, which is shaped like a comma. This shape is due to the head and thorax being merged together, with the abdomen curving around underneath. As a pupa, the mosquito has developed respiratory trumpets that allow it to breathe by coming up to the surface for air like the larva stage. They swim by flipping their abdomen in a circular direction, giving them the nickname “tumbler.” The pupa move slower and less often than the larva since they do not eat throughout this stage of their life cycle, instead utilizing their energy to transform into adults. After several days as a pupa, the mosquito rises to the water surface where the thorax and head separate and the adult mosquito emerges.
In the Lab’s Insectary, we raise species from both Aedes and Anopheles mosquito genus for research. These mosquitoes are utilized in a variety of ways ranging from developing new processes in mosquito rearing, to better understanding the mosquito life cycle to help reduce malaria and other mosquito-borne diseases, to serving as subjects for testing our photonic fence. Check back soon to learn more about the unique and fascinating work we do with mosquitoes.