Culex

Culex is a large and diverse genus of mosquitoes found across the globe. They exist in almost every environment except for the extreme northern parts of temperate zones. In certain major United States cities, such as Los Angeles, they are the most common mosquitoes people encounter. This group is biologically significant because many species act as vectors. A vector is an organism that carries and transmits diseases to other living things. Culex mosquitoes can pass various illnesses to humans, birds, and other animals.

The life cycle of a Culex mosquito follows a process called holometabolism. This is a type of complete metamorphosis where the insect changes form entirely. In warm weather, this developmental cycle usually lasts about two weeks. The process begins when a female lays eggs in rafts on the water's surface. A single raft can contain as many as 300 eggs. These eggs are dark brown and shaped like tiny cigars. They stick together through adhesion forces rather than using a special cement.

Once the eggs hatch, the insect enters the larval stage. These larvae are obligately aquatic, meaning they must live in water to survive. They have a linear body shape and stay mostly vertical in the water. They maintain this position by moving their bristly mouthparts. To move through the water, the larvae lash their bodies back and forth. During this stage, they feed on plant material, microscopic organisms, or organic matter. After several instars, which are developmental stages, they become pupae.

The pupa stage is distinct because the insect changes its physical shape. Unlike the long larvae, the pupae are comma-shaped. They do not eat food during this period of development. However, they are very active and can swim with rapid, jerking motions to avoid predators. The pupa must stay in contact with the water surface to breathe. It must also avoid becoming desiccated, or dried out. After 24 to 48 hours, the pupa ruptures. The adult mosquito then emerges from the shed exoskeleton.

Adult Culex mosquitoes belong to the suborder Nematocera. Their bodies have a clearly defined head, thorax, and abdomen. When they are at rest, they hold their two forewings horizontally over their abdomen. Like all flying insects in the order Diptera, they have a second pair of wings that are modified. These tiny, inconspicuous structures are called halteres. Scientists often identify them by measuring bodily proportions or checking for specific bristles. In the field, researchers often distinguish them from Anopheline mosquitoes by looking at their wings and palps.

There are several ways to tell a Culex mosquito apart from its relatives. One major difference is the length of the maxillary palps, which are parts near the mouth. In female Anopheline mosquitoes, the palps are as long as the proboscis. However, female Culicine mosquitoes, the group including Culex, have short palps. You can also look at the wings; Anopheline wings often have spots, while Culicine wings are usually clear. Furthermore, Anopheline mosquitoes often sit with their heads low and rear ends raised. In contrast, Culicine females keep their bodies in a horizontal position.

Culex species are known for transmitting many different types of diseases. They are vectors for several arboviruses, which are viruses transmitted by arthropods. These include West Nile virus, Japanese encephalitis, and St. Louis encephalitis. They also transmit equine encephalitides, such as Western and Eastern equine encephalitis. Some species carry nematode infections, specifically forms of filariasis. They can also carry protist parasites, such as avian malaria, which affects birds. In China, Culex mosquitoes have been linked to the Cat Que Virus, which affects pigs.

This genus is incredibly vast and continues to be studied by scientists. Carl Linnaeus originally named the genus using the Latin term for a midge or gnat. Today, the genus comprises over 20 subgenera and includes well over 1,000 different species. New species are frequently described as researchers find them. Even their behavior is being studied, such as how they find hosts. Scientists have found that a compound called nonanal attracts them. This compound works synergistically, or together, with carbon dioxide to help the mosquito find its target.