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Can mosquitos bite in self-defense?

Can mosquitos bite in self-defense?


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When chasing away wasps or bees there is a danger of them stinging us in self-defense. Can a similar danger arise when chasing away a mosquito which is otherwise not hungry? I understand that mosquitoes bite to feed (by sucking blood), but do they use their bites in self-defense against large targets, like humans? Mosquito bites can be somewhat painful or at least uncomfortable, and can carry dangerous diseases, making them theoretically viable as a self-defense weapon.


Probably not. An immediate defense against predators requires an immediate response. The sting of Hymenoptera like the wasps and bees has an immediately painful reaction. In addition, in the eusocial (colony-forming) species, multiple individuals typically contribute to defense of their nest. One sting may not deter a predator or invader but dozens or hundreds of stings would create an immediate deterrent. See for example this paper by [Breed et al. (2004)] on the defense behavior of honey bees. Animal bites that are immediately painful, such as an ant bite or dog bite create an immediate response in the organism being bitten. Spines and thorns on plants deter organisms from biting the plant. Odors released by skunks and some insect provide an immediate response.

The bite of blood-sucking mosquitoes does not provide an immediate deterrent. (Not all mosquitoes suck blood.) This paper by Ramasubramanian et al. (2008) provides a detailed explanation of how a mosquito penetrates the skin. The paper is related to microneedle design but they are using the mosquito as a comparison for painless needle design. Go to page 3 to get a description of the mosquito anatomy and piercing behavior. Comparison of painless microneedle design to the mosquito's proboscis is instructive.

The proboscis is the set of modified mouth parts the mosquito uses to penetrate the skin and suck the blood. The study states that microneedles that penetrate human skin less than 1.5mm is usually painless or effectively so. These needles have a very small diameter, only about 40-100 micrometers in diameter, similar to the width of a human hair. The mosquito's proboscis is about 1.5-2.0 mm long. The diameter of the various structures used to cut through the skin and suck the blood are all less than 40 micrometers in diameter. Thus, the size of the mosquito's proboscis is so small that it does not cause immediate pain, or the pain is so little that it is an annoyance at best. In addition, the proboscis is weak enough that the moquito may have to probe the skin several times before a spot suitable for penetration can be found.

Finally, only the females of blood-sucking mosquitoes feed on blood and have the penetrating mouth parts. Males do not. They feed entirely on nectar and water. Males would thus not be capable of such defense.


Understanding the Life Cycle of the Mosquito

Mosquitoes (Order Diptera, Family Culicidae) are some of the most adaptable and successful insects on Earth and are found in some extraordinary places. Virtually any natural or man-made collection of water can support mosquito production. They’ve been discovered in mines nearly a mile below the surface, and on mountain peaks at 14,000 feet, and if you know where to look, there is a good possibility that there are mosquitoes breeding in your own backyard. Not every species of mosquito causes problems for people, but many have profoundly negative effects. Mosquitoes can be distinguished easily from other flies by the fact that they have both a long, piercing proboscis and scales on the veins of their wings. Approximately 176 species of mosquitoes are found in the United States, with more than 3,000 species known throughout the world. In the United States, only a few of these species are important as carriers of disease, but many more are important nuisance species that dramatically affect peoples’ quality of life.


Mosquito-Borne Diseases

Protecting workers from mosquito bites can prevent diseases.

Mosquito-borne diseases are those spread by the bite of an infected mosquito. Diseases that are spread to people by mosquitoes include Zika virus, West Nile virus, Chikungunya virus, dengue, and malaria.

Employers should protect workers and workers should protect themselves from diseases spread by mosquitoes. Although people may not become sick after a bite from an infected mosquito, some people have a mild, short-term illness or (rarely) severe or long-term illness. Severe cases of mosquito-borne diseases can cause death.


Data May Help Mosquito Control in the Future, but More Research Is Needed

The researchers hope the insights can be used to help develop new methods for mosquito control and lower the spread of mosquito-borne diseases in the future, they note in the study.

The results offer new insight into how mosquitoes compensate for having relatively poor eyesight, and it’s possible that more research might one day yield new methods of mosquito control (and therefore lowering the spread of mosquito-borne disease), says Antoine Cribellier, a PhD candidate researching mosquito flight at the University of Wageningen in the Netherlands who wasn’t involved in the study.

One such direction he and his colleagues are studying are ways to trap mosquitoes. Knowing more about mosquito host-seeking behavior will help those efforts, he says. Reducing the number of mosquitoes in a given area can also help, he adds. “An easy and very efficient way of doing that is to get rid of any standing water (like a rain bucket in your garden) where females can lay their eggs.”

Unfortunately, he adds, “this study doesn’t tell us much about ways for people to avoid mosquito bites.”

To repel mosquitoes, it’s necessary to either mask the scent from the hosts (you and me) that attracts the insects to begin with, or to interfere with mosquitoes’ sensory systems, explains Joseph Conlon, a technical adviser for the American Mosquito Control Association, who was not involved in the new research.

“I don’t necessarily find any earthshaking data [from this research] that should influence personal protective measures.”

What experts do recommend to avoid mosquito bites is:

  • Cover arms, legs, and other exposed skin
  • Use insect repellents
  • Stay indoors at dawn and dusk (when mosquitoes tend to be most active)
  • Use a fan or find an area that is breezy (mosquitoes are weak fliers a little airflow can help keep them away)

One limitation of the study is that mosquitoes were tethered in a controlled environment in a lab, and it’s possible their flight responses might be different in the open air. Also, the Aedes aegypti is a species of mosquito that is active during the day, and it’s possible results might differ for mosquitoes that come out at night, Conlon notes.


Can Synthetic Biology Make Mosquito-Borne Diseases a Thing of the Past?

Mosquitoes are major vectors of animal-to-human disease transmission. DARPA is funding a synthetic . [+] biology initiative to develop a long-lasting, bio-based mosquito repellent.

Indian Council of Medical Research

Over five million people worldwide die from vector-borne diseases every year. Vector-borne diseases, such as malaria, dengue, and Zika, are pathogens that can be transmitted through the bite of an insect. Though vaccines for some of these illnesses are in development, current prevention options are very effective.

To address this issue, the Defense Advanced Research Projects Agency (DARPA) is looking at synthetic biology as a method to find an easy to use, cost-effective solution.

In a recent announcement, DARPA awarded Ginkgo Bioworks, Azitra, Latham BioPharm Group, and Florida International University (FIU) a contract of up to $15 million to create a novel, long-lasting mosquito repellent using engineered microbes. This partnership is a part of DARPA’s ReVector program that supports groundbreaking technologies to protect US troops from mosquito-borne illnesses.

A Military Upgrade For Bug Spray

This map shows how many of the 6 most common vector-borne diseases could potentially affect . [+] populations in 5 square kilometers sections. Tropical regions like South Africa, Western Sub-Saharan Africa, and Southeast Asia are particularly vulnerable.

Infections like malaria are not commonplace in temperate regions like the United States. High mosquito populations—and therefore higher instances of disease—are more common in tropical and subtropical regions. However, many US troops operate in these hotbed locations, hence DARPA’s motivation for the project.

Currently, all available mosquito repellents fall short in providing long-lasting, effective protection. They require an application to the skin every few hours and are impractical for use in the field. ReVector’s new project hopes their microbe-based solution will protect against mosquito bites for at least two weeks, skipping the need for continuous reapplication.

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Why Choose Synthetic Biology?

As a field, synthetic biology is well placed to develop a novel, bio-based approach to disease prevention. One of the biggest sectors of biotech innovation is microbe engineering. By modifying a microbe’s tiny cellular factories, research teams can genetically engineer organisms to produce a wide range of materials. Using computing and big data, synthetic biologists can rapidly prototype and iterate on different solutions to produce the desired molecule.

Ginkgo Bioworks will take the lead as the primary contractor for the project. Ginkgo is well known in the synthetic biology industry and beyond for providing biotech infrastructure as a service—similar to Amazon Web Services but for biology. Rather than producing the final products itself, Ginkgo designs and engineers microbes for a wide range of customer needs. For this project, Ginkgo will leverage their organism foundries—the company’s automated platforms for microbe design and validation—to engineer microorganisms found on human skin.

Unlocking the Skin Microbiome

Zach Smith, Director of Government Business at Ginkgo Bioworks, the leading contractor in DARPA’s . [+] ReVector program initiative.

The human skin microbiome is a diverse neighborhood of microorganisms that protect against dermatological diseases. Each microorganism occupies a wide range of skin niches and plays a specific role in educating the billions of skin cells on how to respond to pathogenic outsiders.

Zach Smith, Director of Government Business at Ginkgo Bioworks, gave insights into the project’s approach. “There are two ways to deal with mosquitoes, you can repel them or you can isolate the signals humans give off to attract mosquitoes and weaken them. We are planning to do both,” says Smith.

Using high throughput testing, Ginkgo aims to rapidly discover the best combination of engineered microbial compounds to produce a Live Biotherapeutic Product (LBP). But, even with an LBP, humans still naturally produce byproducts that attract insects.

Humans give off heat, carbon dioxide, and certain chemical elements and compounds called volatiles that vaporize rapidly off the skin. If the compounds remain volatile, the repellent would only diminish the number of mosquitoes a person attracts rather than deterring them entirely. However, if these volatile compounds can be identified, the project team could produce a repellent with additional properties that prevent these compounds from vaporizing in the first place.

A Fullstack Partnership

In the initial research phase of the project, Ginkgo plans to collaborate with top mosquito researcher and neurogeneticist Matthew DeGennaro, Ph.D., of FIU’s Biomolecular Sciences Institute. As an expert in molecular genetics and the odor attraction profile of mosquitoes, DeGennaro can provide unique insights into the molecular compounds needed to repel mosquitoes long-term.

Matthew DeGenarro, Ph.D., of Florida International University will provide key neurogenetic insights . [+] to the ReVector project.

Florida International University

Though popular products like DEET are considered effective, mosquito repellent technology hasn’t been updated in decades. “DEET has been the gold standard for mosquito repellency since the 1940s. Over the past 80 years, [the science community] has learned so much more about how mosquitoes find their hosts,” said DeGennaro in a press release. For Ginkgo, understanding the complex relationship between humans and mosquitoes at the microbial level will be key to the company’s bioengineering process.

As the research progresses, Azitra, a clinical-stage medical dermatology company, will leverage its extensive scientific knowledge of the skin microbiome to develop and characterize various bacterial strains. To ensure the whole project runs smoothly from beginning to end, Latham BioPharm Group will provide extensive program management, systems integration support, and regulatory strategy expertise.

Project Validation: Testing, Testing, 1,2, 3

The project is a four-year effort organized into three key phases. First, the team will work to produce and test as many potential repellents as possible. Ginkgo will take whichever repellents show the most promising results and produce more microbe variations until they identify a select few microbe strains with the strongest repellent properties.

Additionally, some microbes that may be less effective in repelling mosquitoes may be better at masking volatiles. Understanding the different properties of the microbes will be essential in engineering a final product. Once this microbial cohort is identified, the team will begin community modeling of the skin to ensure the microbe strains can persist symbiotically on the skin for at least two weeks.

Finally, when the best microbes are identified and verified for safety, human participants will apply the repellent onto their arms and stick them into a container of mosquitoes. If the mosquitoes aren’t attracted to the human skin, the repellent will be doing its job. Though it sounds deeply unpleasant for the human participants, it’s also an easy, low-tech way to ‘field test’ the product.

Looking Beyond Mosquitoes: A New Approach To Skin Protection?

If the team can develop a suitable repellent, the applications could have significant, far-reaching benefits. Jason Kelly, Ginkgo Co-founder, and CEO summed up the technology’s potential in a recent press release. “The ability to program living cells that are part of our natural microbiome, and thus improve our ability to fight off challenges like mosquito vectoring of disease, has enormous potential in global health. Our research in collaboration with Azitra, FIU, and LBG could be transformative to the next generation of living medicine.”

The protocols and lessons learned from this project could produce a genetic toolkit for leveraging the skin microbiome against other vector-borne diseases. Though the COVID-19 pandemic isn’t a mosquito-transmitted illness, the importance of preventing animal-to-human pathogens is painfully clear. If successful, ReVector’s synthetic biology initiative could blaze a trail for other biotherapeutics.

For Ginkgo’s Zach Smith, the applications for microbiome technology aren’t necessarily limited to disease prevention. Smith is especially interested in bioengineered sunblock. “We don’t know if it is possible, but if it is a [sun] repellent that lasts a day, it would be a game-changer for me and my skin,” says Smith.

The potential of leveraging skin microbes against disease and damage is only just beginning to be explored. Even if the project avoids setbacks, it will be years before this technology reaches the military. And it will likely be even longer before civilian populations benefit, if they do at all. ReVector’s project also does not indicate whether or not the end product could become available in developing countries where robust mosquito repellents are sorely needed.

But the partnership also demonstrates how far synthetic biology has grown as an industry. This is not the field’s first partnership with DARPA. But the broad coalition of biotech companies and experts is a promising marker of growth in the bioeconomy. Though it’s too early to hang any hats on, this new venture could represent a milestone for both synthetic biology and the long-enduring fight against some of our world’s most deadly pathogens.

I’m the founder of SynBioBeta, and some of the companies that I write about are sponsors of the SynBioBeta conference and weekly digest, including Ginkgo Bioworks. I’m also an Operating Partner at DCVC which is an investor in Ginkgo Bioworks. Thank you to Vinit Parekh for additional research and reporting in this article.


Behind the bite: How Hidalgo County is combating mosquito infestations

The warmer months often bring rains and rising temperatures which create the perfect breeding grounds for mosquitoes to thrive in stagnant waters, especially in a subtropical climate such as the Rio Grande Valley.

To combat these pests, the city of McAllen’s Environmental Health and Code Enforcement Department have begun spraying areas with a high population of mosquitoes.

The slow moving trucks equipped with tanks filled with a mix of Permethrin, the most commonly used insecticide, and oil or water, drive late at night into the early morning to avoid traffic and pedestrians.

Ten individuals within the department are licensed by the Texas Department of Agriculture to spray the insecticide as part of state regulation.

“Another state regulation is that we can not spray if wind speeds are greater than 10 miles an hour,” Steven Kotsatos, director at Environmental Health and Code Enforcement, said Thursday. “We don’t want the insecticide drifting … we want to go down the center of a street or an alley and let the spray stay there and rise up.”

Kotsatos also said they rotate through different chemicals in order to fight any insect that might have grown resistant to a specific pesticide and are currently in the process of rotation.

In addition to the city’s efforts to control mosquito breeding, the University of Texas at Rio Grande Valley’s Center for Vector-Borne Diseases, is constantly collecting larvae from McAllen and other areas along the eastern half of the U.S.-Mexico border to test their susceptibility to commonly used pesticides.

McAllen health and code inspector Arcelia Canales tests equipment before spraying for mosquitos at the city’s Development Center on Thursday in McAllen. (Joel Martinez | [email protected])

The city of McAllen collects mosquitoes from its areas to give to the lab by setting gravid traps which lure in mosquitoes that carry West Nile virus.

A gravid trap attracts female mosquitoes by creating an ideal environment for them to lay their eggs.

The trap creates an upward current of air to carry the mosquitoes from the pan into a collection bag.

Another method used by Valley collectors is a carbon dioxide trap which attracts mosquitoes by creating the illusion of a living animal with the use of dry ice.

Christopher Vitek, a UTRGV biology professor, said aside from the insecticide research, the university also regularly tests mosquitoes for diseases in the South Texas Mosquitoes Borne Diseases Surveillance Project, which is funded by the CDC.

Contrary to their bleak reputation as disease transmitters, only five of the 30 mosquito species in South Texas are disease vectors.

The UTRGV office of emergency preparedness attributes Aedes Aegypti mosquitoes or “dusk and dawn biters” as disease carriers in the Valley. This species can be identified by the insect’s white-shaped markings on its legs and thorax.

This species takes as little as a week to mature from an egg into adulthood and has a lifespan of about three weeks. Perhaps the biggest contributor to the Valley’s infestation is that Aedes Aegypti eggs remain viable for over a year in their dry state.

Meaning that even after the rains subside these mosquitoes may re-emerge.

The four most common vector-borne diseases transmitted by mosquitoes in South Texas are Dengue Fever, West Nile virus, Zika virus and Chikungunya virus.

Last year, the Valley had an upsurge of Dengue Fever and Zika cases.

West Nile has proven to be the most prevalent among the viruses on a year-to-year basis.

Despite the constant rainfall over the past several weeks, the Valley has not confirmed any cases of mosquito driven disease in its residents this year.

Dr. Ivan Melendez, the Hidalgo County health authority, said he predicts cases of mosquito-borne disease to begin rolling in within the next couple of weeks due to the excessive amounts of rain.

“I think it’s definitely a significant healthcare contributor,” Melendez said. “It’s definitely worrisome especially in areas where a lot of people are outside or don’t have air conditioning.”

McAllen code inspector Geraldo Valdez prepares to spray for mosquitoes at the McAllen Development Center on Thursday in McAllen. (Joel Martinez | [email protected])

As previously reported by The Monitor, residents should exercise caution when entering mosquito-prone habitats.

Some preventative measures include emptying or getting rid of any containers that may hold stagnant water such as cans, pots, pet dishes, gutters and discarded tires, which have been the subject of illegal dumping despite McAllen residents being allowed to dispose of five tires a month at the recycling center for free.

“It’s not only tires, even the brush that’s leftover from the February freeze is an issue,” Hidalgo County Public Affairs Director Carlos Sanchez said. “It can create stagnant pools of water.”

In addition, pools and hot tubs should be maintained, rain barrels should have screens and tall grass should be cut as these areas can be perfect environments for mosquitoes to lay eggs.

Mosquito briquettes and repellents can also be purchased from stores to help combat infestations.

When applying insect repellent residents should be wary of practicing proper use to avoid ingestion of insecticides. The most effective repellents are those which contain DEET, picaridin, oil of lemon, eucalyptus or IR3535.

Back in March, McAllen’s Environmental Health and Code Enforcement Department also began a monthly educational outreach program where the department goes out to different community centers to teach the public about the top 10 code violations, including dumping of tires, mosquitoes and tall grass and how it all ties into the environment.


Can mosquitos bite in self-defense? - Biology

Mosquitoes are blood sucking insects that are responsible for the transmission of many diseases throughout the human and animal populations of the world. Within Australia there are more than 300 different species of mosquito but only a small number are of major concern. Several important human diseases are transmitted throughout Australia by these insects including Dengue fever, Australian encephalitis, Ross River virus disease and Barmah Forerst virus disease malaria has been transmitted locally in Australia only rarely in recent decades. In addition to being disease vectors, mosquitoes can cause major disruptions, through their persistent biting, to occupational, recreational and social activities.

Mosquitoes belong to the family of flies called Culicidae and are small fragile insects

that have six delicate legs and two wings covered in scales. The head of a mosquito is equipped with a projecting proboscis which conceals and protects the long piercing and sucking mouthparts. These biting insects have a complex life cycle the immature stage is totally aquatic and the adult is terrestrial. The adult female returns to a water habitat for a brief period to lay each batch of eggs. Mosquito species vary in their breeding habits, biting behaviour, host preferences and flight range. Most mosquitoes disperse less than two kilometres some move only a few metres away from their original breeding place, others can fly some 5 or 10 kilometres, and a few species will disperse up to 50 kilometres downwind from the larval habitats.

On average, a female mosquito will live 2-3 weeks, but the male's lifespan is shorter. Within their lifetime both adult male and female will feed on nectar and plant fluids, but it is only the female that will seek a blood meal. The majority of species require this blood meal as a protein source for egg development. Female mosquitoes are attracted to a potential host through a combination of different stimuli that emanate from the host. The stimuli can include carbon dioxide, body odours, air movement or heat. Upon locating a suitable host, the female will probe the skin for a blood capillary then inject a small amount of saliva containing chemicals which prevent the host's blood from clotting. This is often the pathway for potential pathogens such as viruses to enter a host. After engorging on the host's blood the female will find a resting place to digest her meal and develop eggs before flyingoff to deposit them in a suitable aquatic habitat.

On hatching, the young larvae (wrigglers) feed continuously and grow through four different instars or moults. Larval development is dependent on the availability of food and prevailing conditions, particularly temperature, but generally takes at least one to two weeks. The final larval instar develops into an active comma-shaped pupa (tumbler) from which the adult mosquito emerges about 2 days later to feed, mate and develop eggs for the next generation.


Mosquito-borne diseases in Australia

Diseases transmitted by mosquitoes in Australia include Dengue fever, Australian encephalitis, Ross River (RR) virus disease and Barmah Forerst (BF) virus disease. Dengue is the most important viral disease transmitted by mosquitoes afflicting humans in a world context. Clinical symptoms range from mild fevers, to a severe and potentially life threatening haemorrhagic disease. In Australia, Dengue fever is restricted to Quensland where the major vector Aedes aegypti occurs. "Australian encephalitis" (AE), or "Murray Valley encephalitis" are synonyms for a clinical syndrome caused by infection with Murray Valley encephalitis virus or Kunjin virus. Symptoms are variable, from mild to severe with permanent impaired neurological functions, to sometimes fatal. Cases of AE occur sporadically in northern Australia and especially in the northwest of WA, but there have been no cases of MVE recorded in southeastern Australia since 1974. Ross River and Barmah Forest disease have been collectively known as "Epidemic Polyarthritis", however the two diseases have a slightly different clinical picture. A wide variety of symptoms may occur from rashes with fevers, to arthritis that can last from months to years with RR virus infection. RR disease is the most commonly reported mosquito transmitted disease to humans (over 6,500 cases in 1997) and occurs in all states of Australia. There are occassional local epidemics with hundreds to thousands of infections, with many going unreported. BF disease occurs in most states of Australia, although the annual number of cases are around 1/10th that of RR disease. A series of outbreaks during the early 1990's has highlighted the increasing importance of BF disease. Malaria in Australia has been endemic, but was declared eradicated from the country in 1981. However, approximately 700-800 cases are imported annually from travellers infected elsewhere.


Clinical Presentation

Sensitivity to mosquito bites varies with individuals, most people have only a mild reaction but others can have severe symptoms from the saliva of mosquitoes. Typical symptoms include swelling, redness and irritation at the puncture site. If the bites are scratched or traumatized, they may become infected with bacteria and a secondary infection can be initiated, especially on the lower limbs. The diagnosis of mosquito-borne diseases including Dengue, Australian encephalitis, and Ross River and Barmah Forest viruses can only be confirmed with appropriate blood tests.


Laboratory Diagnosis

Mosquitoes are identified with the aid of a stereo microscope and taxonomic keys. The detection of viruses and other pathogens in mosquitoes is undertaken. Detection of viruses or virus antibodies in human blood is a procedure performed in the arboviral serology unit at Westmead Hospital.


Treatment and Control

There are many methods of control that can be implemented to reduce the number of mosquitoes. Local councils may use larvicides (pesticides that kill the larvae) which prevent mosquitoes from maturing to adults. In areas where there is a disease outbreak fogging may be considered as an option in order to kill the infected adult mosquito population. Other methods could include the use of parasites, predators or pathogens of mosquitoes to assist in reducing the population, but there is no biological control agent other than fish currently available for use against mosquitoes.

Simple measures can be taken by individuals to limit their contact with mosquitoes, Areas that are known to be infested with large numbers of mosquitoes shold be avoided. Activities that are scheduled for outdoors, especially around dusk should be limited, as the biting activity of many mosquitoes will peak during this period. Clothing that has long sleeves and long pants should be worn when visiting areas that are infested with mosquitoes. A chemical repellent should be used on exposed areas of skin, but not repeatedly on young children. See "Beathing the Bite of Mosquito-borne Disease, A Guide To Personal Protection Strategies Against Australian Mosquitoes" for detailed information on the appropriate use of repellents.

Windows and doors should be screened water tanks also, using a small gauge mesh to exclude mosquitoes from these potential breeding sites. Empty all containers throughout the garden that hold water such as pot plant saucers, tyres, roof guttering and tins to prevent breeding. Bed nets are an effective barrier against biting insects at home or camping, and can now treated safely with an insecticide. Insecticidal sprays, and coils and electric mats, for use around the house can help in keeping mosquitoes at bay.


Confirmation and Enquiries

Identification of mosquitoes and all other medically important arthropods is preformed through the Medical Entomology Department at ICPMR, Westmead Hospital.


General Mosquito Biology

The mosquito has four distinct stages in its life cycle: egg, larva, pupa, and adult. The adult is an active flying insect, while the larvae and pupae are aquatic and occur only in water. Depending on the species, eggs are laid either on the surface of water or are deposited on moist soil or other objects that will often be flooded.

One factor common to all mosquito species is that eggs are laid in association with free water or on a moist surface. Eggs are white when first deposited, darkening to a black or dark brown within 12-24 hours. Single eggs are about 1/50 inch (0.5mm) long, and those of most species appear similar when seen by the naked eye (one exception is the Anopheles spp. whose eggs have floats attached to each side of the egg). Eggs are laid singly by some species, and others lay eggs together to form rafts. The incubation period (time between when eggs are laid and when they hatch) may vary considerably among species. Eggs of permanent-water mosquitoes where eggs are deposited on the water surface may hatch in 1-3 days depending on temperature. Floodwater species deposit their eggs on moist soil or another wet substrate and have a wide variation in incubation periods. These eggs will not hatch until submerged by rising water caused by rainfall, melting snow in the spring, or other floodwater. Depending on the species and conditions these eggs may hatch the next time they are flooded, as soon as ten days, or may not hatch until they are flooded a year or more later.

Larvae

The larvae (wigglers or wrigglers) of all mosquitoes live in water and have four developmental periods or instars. These are called 1st, 2nd, 3rd, and 4th instars with each succeeding stage larger than the last. At the end of each instar, the larva sheds its skin by a process called molting. The larva is an active feeding stage. Larvae feed on particulate organic material in the water. The larvae of most species have a breathing tube (click here for larval anatomy) and must occasionally come to the surface of the water to get oxygen. The total length of time that larvae spend in the larval stage depends on the species and the water temperature. Some can develop in as little as 5 or 6 days. Upon maturity the 4th instar larvae molts into the pupal stage.

Aedes albopictus (left), Culex spp.(right)

Pupae

Unlike most other insects, the mosquito pupa is very active, and, like the larva, lives in water. It differs greatly from the larva in shape and appearance. The pupa has a comma-shaped body divisible into two distinct regions. The front region consists of the head and thorax (cephalothorax) and is greatly enlarged. It bears a pair of respiratory trumpets on the upper surface. It must periodically come to the surface to get oxygen. The second region is the abdomen which has freely-movable segments with a pair of paddle-like appendages at the tip. Feeding does not take place during the pupal stage. The pupal stage only lasts for a few days and is the stage when all the larval tissues change into the adult tissues. The adult emerges directly from the pupal case on the surface of the water.

Aedes albopictus (left), Anopheles spp. (right)

Adult

The adult mosquito is entirely terrestrial and is capable of flying long distances. Both females and males feed on nectars which they use for energy. Males and females mate during the first 3 to 5 days after they have emerged. Females mate only once. Males generally live for only a week. Only the females feed on blood, which is what is occurring when they are biting. Females evidently gain little nourishment from blood meals but need them in order to develop eggs. Many mosquitoes feed on any warm-blooded bird or mammal. However, some prefer cold-blooded animals. Some species also prefer birds and seldom feed on mammals, which is the case with Culex spp. mosquitoes which are known to transmit the West Nile virus (WNV). Unfortunately many species feed on a wide range of warm-blooded mammals and humans are often attacked. Once a female has completely engorged she flies to a shaded environment until her eggs are completely developed, usually 3 to 5 days. Once the eggs are developed the female is called a gravid female and she begins to search for a desirable place to lay her eggs. If a female survives her egg laying activities, she will very soon start searching for another blood meal after which she will lay another batch of eggs. She does not need to mate a second time. Generally a female will only live long enough to lay 1 to 3 batches of eggs.

Most mosquito species are actively searching for a blood meal in the evening hours from just before dark until 2 to 3 hours after dark. During the daytime the females normally rest in cooler vegetated areas where the humidity is higher and they are protected from drying out. Females will often bite in the daytime if humans or animals invade the wooded areas where they are resting. However, Aedes albopictus is an aggressive biter which prefers to feed during the daylight hours and is often a nuisance in urban areas.

Aedes albopictus female (left), Aedes albopictus male (right)

Aedes albopictus, Asian Tiger Mosquito (left), Culex quinquefasciatus, Southern House Mosquito (right)


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Vaccine to Protect Broadly Against Mosquito-Borne Diseases Appears Safe in Early Trial

The vaccine is designed to induce an immune reaction against peptides in mosquito saliva—like that in these Aedes mosquitoes.

The vaccine is designed to induce an immune reaction against peptides in mosquito saliva—like that in these Aedes mosquitoes.

In a new study published this week in The Lancet, NIAID scientists describe the results of a small Phase 1 trial of a vaccine designed to provide broad protection against mosquito-borne diseases. The trial indicated that the vaccine is safe and induces a strong immune response in healthy volunteers.

Unlike other experimental vaccines for mosquito-borne diseases, this experimental vaccine (known as AGS-v) is designed to provoke an immune response against mosquito saliva, rather than any specific parasites, viruses, or bacteria the mosquito might transmit. Ordinarily, when a mosquito bites a person, the natural immune response to the mosquito saliva helps pathogens carried in the saliva to evade the body’s immune response. With this vaccine, the immune system is trained to respond differently to mosquito saliva, and the pathogen is no longer able to hide from activated immune cells. Developed by the London-based pharmaceutical company SEEK via its subsidiary, Imutex Limited, and produced by CordenPharma (based in Liestal, Switzerland and in Caponago, Italy), the vaccine contains four synthetic peptides that can also be found in mosquito salivary gland proteins. The double-blind study, which began in 2017 at the NIH Clinical Center in Bethesda, Maryland, was led by NIAID’s Laboratory of Infectious Diseases Clinical Studies unit, in collaboration with the Vector Molecular Biology Section.

The double-blind study was the first trial of this so-called “universal mosquito vaccine” in humans. Forty-nine healthy volunteers enrolled in the study and were randomly assigned to one of three groups. One group received two injections of a placebo (sterile water), one group received two injections of the vaccine, and one group received two injections of a combination of the vaccine and an adjuvant. Addition of the adjuvant generates a water in oil emulsion, which is commonly added to vaccines to enhance immune responses. In all groups, the two subcutaneous injections were given 21 days apart.

On the 42 nd day of the study, volunteers underwent a “feeding session” with disease-free mosquitoes, which had been bred in captivity at the NIH. The mosquitoes were placed into a contained feeding device (resembling a cup) and fed briefly from volunteers’ arms through a fine mesh. Volunteers were monitored after each vaccination, after the feeding session, and at regular follow-up visits for twelve months after the first vaccination. The mosquitoes were also monitored after the feeding session, to see whether the vaccine had any impact on their survival and the number of offspring they produced.

None of the volunteers had serious adverse reactions to the vaccine or mosquito feeding, although one volunteer did develop a significant rash after the first dose of the vaccine.

The volunteers’ blood tests showed that the vaccine in combination with the adjuvant produced a significant immune response to mosquito salivary peptides. Further, this immune response was not accompanied by a worse reaction to mosquito bites volunteers reported only the usual itching and discomfort after their mosquito feeding sessions.

The authors say the study’s results are promising and suggest that further research to test the vaccine’s efficacy against individual pathogens, followed by larger field studies, would be worthwhile. A widely available “universal” vaccine could provide protection against emerging and re-emerging mosquito-borne diseases as they arise, allowing public health officials to quickly respond to new outbreaks and epidemics without waiting for new treatments or vaccines to be developed.

J. Manning, et al. Safety and immunogenicity of a first-in-human mosquito saliva peptide vaccine: a randomized, placebo-controlled, double-blind Phase 1 trial. The Lancet. DOI: 10.1016/S0140-6736(20)31048-5 (2020)



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