INTRODUCTION:- Mosquitoes may seem like just another annoying pest. However, there is much more to these small flies than meets the eye. Mosquitoes are actually part of the family Culicidae, which comprises around 3,600 different species. The word “mosquito” comes from the Spanish word “little fly”, and refers to the small size of these insects.
Mosquitoes have a slender, segmented body, one pair of wings, one pair of halteres, and elongated mouthparts. The mosquito life cycle consists of four stages: egg, larva, pupa, and adult. Eggs are laid on the surface of water, and hatch into motile larvae that feed on aquatic algae and organic material. These larvae are important food sources for many freshwater animals, such as dragonfly nymphs, fish, and some birds.
The adult females of most mosquito species have tube-like mouthparts that can pierce the skin of a host and feed on blood. Mosquitoes feed on the blood of a variety of hosts, including mammals, birds, reptiles, amphibians, and some fish. The mosquito’s saliva is transferred to the host during the bite, and can cause an itchy rash. In addition, mosquitoes can ingest pathogens while biting, and transmit them to future hosts.
Mosquito features
Unfortunately, mosquitoes are important vectors of parasitic and arboviral diseases. Eg. malaria, filariasis, yellow fever, Chikungunya, West Nile virus, dengue fever, and Zika. Mosquito-borne diseases. These causes the deaths of over 700,000 people each year, making mosquitoes the deadliest animal on the planet. It has been claimed that almost half of the people who have ever lived have died of mosquito-vectored disease. But more conservative estimates place the death toll closer to 5% of all humans.
Mosquitoes are most active in temperatures between 15 and 25 degrees Celsius (60 and 80 degrees Fahrenheit). They cannot live or function properly when the air temperature drops below 10 degrees Celsius (50 degrees Fahrenheit).
To protect against mosquito-borne diseases, it is important to take measures such as wearing protective clothing, using mosquito nets, and applying insect repellent. By taking these precautions, we can help reduce the spread of mosquito-borne diseases and protect ourselves and others from their deadly consequences.
History
Mosquitoes have been around for a very long time, with the oldest known species dating back to the Late Cretaceous period, around 99 million years ago. Three species of Cretaceous mosquitoes have been identified so far, with the earliest two, Burmaculex antiquus and Priscoculex burmanicus, found in Burmese amber from Myanmar. The third species, Paleoculicis minutus, was discovered in Canadian amber from Alberta, Canada. Molecular estimates suggest that the split between the two subfamilies of mosquitoes, Anophelinae and Culicinae, occurred 197.5 million years ago during the Early Jurassic, but diversification didn’t take place until the Cretaceous.
There are over 3,500 known species of mosquitoes, which are divided into two subfamilies: Anophelinae and Culicinae. These subfamilies contain 43 different genera. The distinction between the two subfamilies is important because they tend to differ in their significance as vectors of different classes of diseases. Arboviral diseases like yellow fever and dengue fever tend to be transmitted by Culicine species, while Anophelinae species are important vectors of malaria and filariasis. The mosquito Anopheles gambiae is currently undergoing speciation into two molecular forms, M(opti) and S(avanah), which has led to some pesticides becoming ineffective against one or the other form.
Family
Mosquitoes belong to the family Culicidae, which comes from the Latin word “culex” meaning “midge” or “gnat”. They share some similarities in appearance with other nematoceran flies such as crane flies and chironomid flies. The family is divided into two subfamilies: Anophelinae and Culicinae, which comprise 112 genera of mosquitoes. Some of the common genera include Aedes, Anopheles, Culex, and Mansonia.
There are over 3,500 known species of mosquitoes, and they have been extensively studied for their role as vectors of diseases such as malaria, dengue fever, and Zika virus. Recent genomic analysis suggests that mosquitoes carry a large number of transposable elements, which could have implications for genetic manipulation strategies aimed at controlling mosquito populations.
Morphology
Mosquitoes have a pair of wings, covered with distinct scales on the surface. Their legs are long and thin, and they have slender bodies that are typically 3-6 mm in length, with dark grey to black coloring. Some species have specific morphological patterns. When at rest, mosquitoes tend to hold their first pair of legs outward. They look similar to midges, which are another ancient family of flies. However, midges, such as Tokunagayusurika akamusi, have larger bodies of similar colors, only one pair of wings, but without scales on the surface. One way to distinguish between the two families of flies is the way they hold their first pair of legs: mosquitoes hold them outward, while midges hold them forward.
DOVELOPMENT
Mosquitoes, like all flies, go through four stages in their life cycle: egg, larva, pupa, and adult. The first three stages are largely aquatic and can last anywhere from 5 to 14 days depending on the species and temperature. However, some mosquitoes can spend part of the year in diapause, delaying their development until there is enough water or warmth. Mosquitoes that live in freezing or waterless regions also spend time in diapause, typically for months.
Adult females of most species lay their eggs in stagnant water. Different species select the situation of the water where they lay their eggs according to their ecological adaptations. Some prefer lakes or temporary puddles, while others breed in marshes or salt-marshes. Some species even breed in natural reservoirs on plants, such as rainwater accumulated in holes in tree trunks or in the leaf-axils of bromeliads.
Certain ecological preferences keep some species of mosquitoes away from humans, whereas others bring them right into houses at night. Some mosquitoes breed in artificial water containers such as casual puddles, and are important breeding places for disease vectors such as Aedes mosquitoes that transmit dengue and yellow fever. Mosquitoes that breed and feed mainly in remote wetlands and salt marshes are less likely to become infected with relevant pathogens and may seldom encounter humans to infect.
Different Stages
Mosquitoes have different ways of laying their eggs, which varies between species. Some species, like Anopheles, lay their eggs individually by flying over the water and dropping them one by one. The eggs of Anopheles are cigar-shaped and have floats down their sides. Other species, such as Culex, lay their eggs in rafts that float on the water’s surface. The female mosquito carefully arranges the eggs to form a head-down array that sticks together to create the raft. Aedes females drop their eggs singly on damp surfaces near the water’s edge, and they do not hatch until they are flooded.
Mosquito larvae have a well-developed head with mouth brushes for feeding, a large thorax, and a segmented abdomen. They breathe through spiracles or a siphon and spend most of their time feeding on microbes in the surface microlayer of the water. Larvae dive below the surface when disturbed and swim through propulsion with their mouth brushes or jerky movements of their bodies. They go through four stages of development before metamorphosing into pupae, and they molt at the end of each instar to allow for further growth.
Life Cycle
Mosquitoes have a complex life cycle with four distinct stages: egg, larva, pupa, and adult. The female mosquito lays her eggs in stagnant water, and the eggs hatch into larvae, which feed on microorganisms in the water. The larva then transforms into a pupa, which does not feed and undergoes metamorphosis before emerging as an adult mosquito.
The adult mosquito has a slender body with three segments: a head, a thorax, and an abdomen. The head is specialized for receiving sensory information and for feeding, with eyes, antennae, and a proboscis. The thorax is specialized for locomotion, with three pairs of legs and a pair of wings. The abdomen is specialized for food digestion and egg development, and females can hold three times their own weight in blood.
Male mosquitoes form swarms, while females seek blood meals to develop their eggs. Mosquitoes can transmit diseases, including malaria, dengue fever, and Zika virus, making them an important public health concern.
Feeding
Mosquitoes, such as Aedes aegypti, are vectors of diseases like dengue fever and yellow fever. Both male and female mosquitoes typically feed on nectar and plant juices, but females have mouthparts adapted for piercing the skin of animal hosts and sucking their blood as ectoparasites. Obtaining a blood meal allows the female to produce more eggs, as it provides concentrated nutrients like proteins. Some mosquito species can reproduce without feeding on blood, while others, such as Anopheles and Aedes, require a blood meal to serve as disease vectors.
Mosquitoes detect their hosts through the organic substances like carbon dioxide and 1-octen-3-ol that they produce, as well as through visual recognition. They are attracted to some people more than others, with factors like blood type, body heat, and body odor playing a role. The mosquito’s sense of smell is key to finding a blood source, with at least 27 types of odor receptors tuned to detect chemicals found in perspiration. Mosquitoes typically feed at dawn or dusk, but some species, like the Asian tiger mosquito, can feed during the day.
During blood feeding, mosquitoes inject saliva into the host to prevent blood from clotting and to offer a route for pathogens to enter the bloodstream. Mosquito bites often leave itchy bumps on the skin, caused by histamines released to fight the protein left behind by the mosquito. Some species of mosquito, such as Toxorhynchites, do not feed on blood and instead prey on the larvae of other mosquito species.
HOST ANIMAL
Mosquitoes are selective feeders that specialize in particular host species, though they often relax their selectivity when they experience severe competition for food, defensive activity on the part of the hosts, or starvation. Some species feed selectively on monkeys, while others prefer particular kinds of birds, but they become less selective as conditions become more difficult.
Mosquito mouthparts are very specialized, particularly those of the females, which in most species are adapted to piercing skin and then sucking blood. Apart from bloodsucking, the females generally also drink assorted fluids rich in dissolved sugar, such as nectar and honeydew, to obtain the energy they need. For this, their blood-sucking mouthparts are perfectly adequate. In contrast, male mosquitoes are not bloodsuckers; they only drink sugary fluids.
Mosquito mouthparts have six parts including the mandibles and maxillae, which are used for piercing the skin, and the hypopharynx and the labrum, both of which are hollow. Saliva with anticoagulant is pumped down the hypopharynx to prevent clotting, and blood is drawn up the labrum.
SALIVA
The saliva of mosquitoes contains a mixture of proteins that help the mosquito obtain a blood meal from its host by blocking the host’s physiological responses. This saliva also contains substances that aid in sugar feeding and control bacterial growth, as well as components that could potentially be useful in developing anti-clotting drugs. Mosquito saliva has been found to modulate the immune response of the host animal, suppressing cytokine production and inhibiting T and B cell proliferation. It can also decrease expression of interferon-α/β during early mosquito-borne virus infection, potentially exacerbating viral infection. Studies in humanized mice suggest that mosquito saliva can also have an impact on human immune system function.
EGG DEVELOPMENT
Mosquitoes need a blood meal to start the process of egg development. After feeding, the mosquito’s gut fills up with blood and the stomach lining secretes a membrane to keep the blood separate from anything else in the stomach. The mosquito can continue feeding on sugar even as the blood meal is slowly digested over several days. The mosquito’s midgut synthesizes enzymes that break down the blood proteins into amino acids, which are used to create egg yolk protein.
In the mosquito species Anopheles stephensi, trypsin activity increases continuously up to 30 hours after feeding, then returns to baseline levels by 60 hours. Aminopeptidase is active in the anterior and posterior midgut regions before and after feeding, and its activity rises in the whole midgut to a maximum at 30 hours after the blood meal. Alpha-glucosidase is active in both anterior and posterior midguts before and after feeding, and its activity increases slowly up to 18 hours after the blood meal, then rises rapidly to a maximum at 30 hours after the blood meal. Proteases are only active in the posterior midgut after blood meal ingestion.
Trypsin is the major primary hydrolytic protease, and it is secreted into the posterior midgut lumen without activation in the posterior midgut epithelium. Aminopeptidase activity is luminal in the posterior midgut, but cellular aminopeptidases are required for peptide processing in both anterior and posterior midguts. Alpha-glucosidase activity is elevated in the posterior midgut after feeding in response to the blood meal, while activity in the anterior midgut is consistent with a nectar-processing role for this midgut region.
Availability Mosquitoes
Mosquitoes are found all over the world, except for Antarctica and some islands with polar climates like Iceland. The absence of mosquitoes in Iceland is due to the country’s unpredictable weather, which does not allow for mosquitoes to complete their life cycle before freezing temperatures set in. Other aquatic Diptera, such as Simuliidae, can survive in Iceland, but they have different habits and adaptations.
Some species of mosquitoes can survive in cold temperatures by taking shelter in suitable microhabitats. Mosquitoes also play a role in pollinating certain flowers. In warm and humid tropical regions, mosquitoes are active all year round, but in temperate and cold regions, they hibernate or enter diapause. Mosquitoes have been introduced into regions where they are not native through human transportation of their eggs, larvae, and pupae in water-filled objects like tires and cut flowers. Quarantine measures have been difficult to implement to prevent the spread of non-native mosquito species.
Distribution of Mosquitoes
Mosquito-borne diseases are influenced by seasonal factors such as temperature, humidity, and precipitation. Climate change can affect these factors and subsequently impact the distribution of mosquitoes. Correlative and mechanistic models are used to predict the spread of mosquito-borne diseases in relation to climate. Currently, these diseases are most prevalent in East Africa, Latin America, Southeast Asia, and India, but there has been an emergence in Europe.
Climate change may make areas of Europe climatically suitable for malaria transmission by 2030 and 2080. Historical records and statistical models can be used to study past and predict future outbreaks and develop interventions to reduce the impact of these diseases.
Mosquitoes: Nature’s Bloodsuckers
Mosquitoes are one of the most common insects found worldwide. These tiny creatures, known for their ability to suck blood, have been around for more than 100 million years. They belong to the family Culicidae and are divided into approximately 3,500 species, each with unique characteristics.
Mosquito-Borne Diseases
Mosquitoes are notorious for transmitting deadly diseases. The most common of these diseases include malaria, dengue fever, chikungunya, Zika virus, and West Nile virus. These diseases are caused by pathogens that are transmitted to humans when female mosquitoes feed on blood.
Malaria is caused by a parasite called Plasmodium, which is transmitted by Anopheles mosquitoes. The disease is prevalent in tropical and subtropical regions, with an estimated 229 million cases reported in 2019.
Dengue fever, chikungunya, and Zika virus are all caused by viruses transmitted by Aedes mosquitoes. These diseases can cause fever, rash, joint pain, and other symptoms.
West Nile virus is transmitted by Culex mosquitoes and can cause flu-like symptoms, including fever, headache, and body aches.
Prevention and Control
Preventing mosquito-borne diseases is critical, given their impact on public health. The most effective way to prevent mosquito bites is by using insect repellents containing DEET, picaridin, or IR3535. Wearing long sleeves and pants can also help reduce exposure to mosquitoes.
Eliminating mosquito breeding sites is essential for reducing mosquito populations. Mosquitoes lay their eggs in standing water, so removing or treating any standing water sources can help reduce mosquito populations.
Insecticides can also be used to control mosquito populations. These can be applied as a spray, mist, or fog, depending on the location and severity of the mosquito infestation.
Conclusion
Mosquitoes are a significant public health concern due to their ability to transmit deadly diseases. Understanding their anatomy, biology, and behavior is crucial for developing effective prevention and control strategies. By taking steps to prevent mosquito bites and reducing mosquito populations, we can help protect ourselves and our communities from the harm caused by these bloodsuckers.