aroma floral

Vampires, mosquitoes and other bloodsuckers

When feeding on blood, it is called hematophagy (from the Greek αἷμα haima “blood” and φάγειν phagein “eat”). It may seem like a strange way of feeding, but the truth is that this strategy is widely spread in the animal world, from mammals to insects, fish and birds. Feeding on the blood of others has evolved independently in various taxonomic groups, perhaps up to 100 different times, giving rise to around 30,000 blood-sucking species. From vampires, to mosquitoes, butterflies, birds , leeches, fleas, ticks, and a myriad of animals that have adapted to these diets.

In order to feed on blood, animals have had to undergo changes in their physiology, morphology and behavior. Blood is rich in protein but poor in vitamins and carbohydrates, which requires special adaptations, both genetic and with communities of bacteria that help them do so. In addition, the blood is extremely rich in iron, which in excess can be toxic, requiring mechanisms to block it and avoid poisoning.

Being a bloodsucker carries great dangers, the main one being detected by the host and ending up crushed by it. To put ourselves in their place, we should imagine how we would approach an animal whose weight is 35 million times our own. We must approach this gigantic mastodon and bite him hard enough to make him bleed. It’s easy to die trying. This relationship is the one that exists between a human weighing 70 kilos and a mosquito weighing 2 milligrams.

Finding the host from which to extract a few drops of blood is not easy either. In a forest, there are possibly hundreds of meters between one mammal and another. On our scale that would be like traveling several kilometers to look for food. City mosquitoes have it easier because we live in high densities. In any case it is a risky activity, and everything and so has evolved multiple times giving rise to a variety of bloodsuckers much greater than that of fictional vampires.

Vampires, draculae and lampreys

Some groups are obligate blood-suckers, that is, they need to feed on blood to survive. This is the case of the so-called vampire bats (Desmodontinae), a group of three species of bat from the American continent that feed only on blood. They eat birds and mammals, including cattle and humans. Once they have located a host, they have an infrared radiation sensor that allows them to detect areas where blood flows close to the skin. With their sharp and sharp incisors they cut into the skin, but they do not cut veins or arteries. Their saliva, like that of mosquitoes, contains blood thinners that prolong bleeding from the incision. However, they do not absorb blood, as mosquitoes do, but instead suck it up. These are the real vampires.

Vampires don’t absorb blood, they lick it

The name “vampire” was used in French to describe them in 1810, in reference to the Slavic folklore that swarmed the Balkans. At the end of the 16th century, the Slovenian writer Janez Vajkard Valvasor documented the existence of a vampire in Istria. The Serbian voice “wampira” (wam = blood, pir = monster) designated the dead man who returned to feed on the blood of his acquaintances. The term entered the German language when Austria gained control of part of the Balkans, and from there the word jumped and became popular in Western Europe, to the point of giving the name of the myth to the American bats that fed on blood. In a script twist, later, the bats ended up impersonating the folk vampire from the hand of the novel “Dracula” by Bram Stoker. In reality, blood-sucking monsters like Dracula, present in many cultures, have nothing to do with true blood-sucking but with our internal fears, of the ancient panic of imagining something taking away our vital energy.

In the waters of the sea there is another group of vertebrates that feed on blood. These are lampreys, fish with an elongated, cylindrical body, without scales, gelatinous, very slippery. They lack a jaw, instead having a circular suction cup mouth with several concentric circles of teeth. With it, they hook onto their prey, scrape their tissues and suck their blood. Its hosts are various sharks, salmon, cod and even marine mammals.

Even among birds we find species that use blood to feed. The vampire ground finch (Geospiza septentrionalis) of the Galapagos Islands is famous for its unusual diet. Occasionally it feeds by drinking blood from other larger birds, pecking at them with its sharp beak until blood spurts. A behavior that possibly evolved from their behavior of cleaning the parasites of these birds, to feeding directly on the birds.

In Africa, Bupaghus erythrorhynchus also occasionally feed on the blood of mammals for which they normally hunt ticks and lice. It has been seen that when allowed to choose between blood and ticks, these birds opt for blood.

Mosquitoes: life beyond blood

Like vampire ground finches, many other organisms are not obligate blood-suckers, being able to obtain nutrients from resources other than blood. This is the case with mosquitoes. These insects digest blood, but they also consume other substances such as nectar or pollen from plants. In fact, male mosquitoes never feed on blood, only females bite, and not in all species, nor is it always the case. Females require blood for the development of their eggs. Their blood doses are higher when previously they have not been able to feed on the sugars provided by the nectar of the flowers.

Anopheles gambiae mosquitoes increase their frequency of bites if they have not had access to sugars before. When they combine both sources of food they live longer, as has been observed in the case of the common mosquito (Culex pipiens), Anopheles sergentii and Anopheles claviger. Despite the change in the frequency of bites, it is unknown whether it implies a reduction in the transmission of pathogens.

The tiger mosquito has a preference for laying eggs in containers with flowers nearby

But there is evidence that in areas where there are a large number of plants rich in sugars, the number of female Anopheles sergentii mosquitoes can be four times higher than in areas without such plants. Although the presence of plants with sugars reduces the number of bites, it also increases their longevity, survival and allows larger populations of mosquitoes, demonstrating the importance of this food source for mosquitoes. And offending an opportunity to regulate mosquito populations by controlling the plant community of an area.

A work carried out with the tiger mosquito (Aedes albopictus) showed that females preferred to deposit their eggs in containers with flowers nearby, than in containers without flowers. Where there were flowers with sugars, there were more eggs. It is suggested that the selection of flowering breeding sites is to provide a safe source of food for the next generation.

Vampires that feed on vampires

Even animals that feed on blood do not escape other animals that feed on their blood. Even mosquitoes are hosts for other organisms that draw blood from them. Bitting midges, small dipterans, have been documented to parasitize mosquitoes, sucking blood from a mosquito’s swollen stomach.

Vampire bats have more parasites than the average of bats, including those known as “bat flies”, which are all related to flies and mosquitoes, they have the appearance of a spider, with a flattened body, without eyes or wings, specialized in sucking the blood of bats.

The practice of hematophagy by itself is not deadly, the animals that practice it never kill their hosts, as fictional vampires do with their victims, but its practice carries a risk: the possibility of transmitting diseases. Malaria, rabies, bubonic plague, dengue, Zika, West Nile fever, typhus and a large number of diseases are transmitted involuntarily by the various animals that feed on the blood of others. It has been seen that some pathogens even modify the smell of the infected organism to make it more attractive to blood-suckers, thus manipulating the vector, but we will talk about that later.

 


References

Barredo E, DeGennaro. 2020. Not just from blood: mosquito nutrient acquisition from nectar sources. Trends in Parasitology 36: 473-484

Davis TJ, Kline DL, Kaufman PE. 2016. Aedes albopictus oviposition preference as influenced by container size and Buddleja davidii plants. Journal of Medical Entomology 53: 273-278

Ebrahimi B, Jackson BT, Guseman JL, Pzrybylowicz CM, Stone CM, Foster WA. 2017. Alteration of plant species assemblages can decrease the transmission potential of malaria mosquitoes. Journal of Applied Ecology 55: 841-851

Fernandes L, Briegel H. 2005. Reproductive physiology of Anopheles gambiae and Anopheles atroparvus. Journal of Vector Ecology 30: 11-26

Greenhall AM. 1972. The biting and feeding habits of the vampire bat, Desmodus rotundus. Journal of Zoology 168: 451-461

Müller G, Schlein Y. 2005. Plant tissues: the frugal diet of mosquitoes in adverse conditions. Medical and Veterinary Entomology 19: 413-422

Plantan T, Howitt M, Kotzé A, Gaines M. 2012. Feeding preferences of the red-billed oxpecker, Buphagus erythrorhynchus: a parasitic mutualism? African Journal of Ecology 51: 325-336

Sterkel M, Oliveira JHM, Bottino-Rojas V, Paiva-Silva GO, Oliveira PL. 2017. The dose makes the poison: nutritional overload determines the life traits of blood-feeding arthropods. Trends in Parasitology 33: 633-644

Stone CM, Taylor RM, Roitberg BD, Foster WA. 2009. Sugar deprivation reduces insemination of Anopheles gambiae, despite daily recruitment of adults, and predicts decline in model populations. Journal of Medical Entomology 51: 1327-1337

Mosquitoes like flowers

Some species of mosquitoes are important transmitters of viral diseases such as dengue, Zika or malaria, to the point of being considered one of the most deadly animals on planet earth. For this reason, many scientific studies have focused on understanding the mosquito-human interaction and, in particular, the sensory responses generated by humans.

Although it is hard to believe mosquitoes not only feed on human blood, in fact flower nectar is their main source of food.

A team of scientists, led by the University of Washington in the United States, has discovered the chemical signals that lead these insects to pollinate a species of orchid particularly irresistible to them. Knowing what you find irresistible could help you develop less toxic and more effective repellents in the future.

Mosquitoes have a very sensitive olfactory system that they use to locate important sources of nutrients, among them the nectar of different flowers or our presence to bite us. While male mosquitoes need nectar to survive, in females the sugar of flowers helps them to increase their life expectancy, survival rate and increase reproduction.

“For male mosquitoes, nectar is their only food source, and females feed on nectar for almost every day of their lives,” says Jeffrey Riffell, professor of biology at the American university

In the study, they examined the neural and behavioral processes of mosquitoes when exposed to flower aromas for which they feel preferences.

  • Pollination studies in the orchid species Platanthera obtusata by mosquitoes of the Aedes group.
  • Analysis of the floral aromatic compounds that attract various species of mosquitoes.
  • Recordings of the electrical activity of mosquito antennas showing how these aromas and compounds are represented and affect their neural activity.

His favorite flower

Some Aedes mosquitoes show affinity for the Platanthera obtusata orchid, being effective pollinators for this species. This association between mosquitoes and orchids provides a unique opportunity to identify sensory mechanisms that help mosquitoes locate sources of nectar.

Orquídea

Platanthera obtusata (Banks ex Pursh) Lindl. 20090624.96 Mount Stearns, Willmore Wilderness, Alberta

During the study they observed more than 581 Platanthera obtusata flowers during 47 hours, in which they were able to register up to 57 times Aedes mosquitoes feeding on them.

The observations were made in northern Washington state, where the Platanthera group orchids and mosquitoes abound.

 

Platanthera obtusata has an aroma reminiscent of grass, while other orchids in the environment, which are less attractive to mosquitoes, have a sweeter fragrance. The height and green coloration of the flowers make this plant difficult to distinguish from neighboring vegetation, yet the mosquitoes still manage to orient themselves and zigzag towards their flowers.

When the researchers covered the plants with bags, to prevent mosquitoes from seeing the flowers, the insects kept trying to reach the plants through the bag. This simple experiment made it possible to verify that the orchid generates a great olfactory attraction on mosquitoes, which led experts to analyze the chemical compounds in its aroma.

“The scent is actually a complex combination of chemicals, that of a rose, for example, consists of more than 300, and mosquitoes can detect the different types of chemicals that make it up,” says Riffell.

The orchids of the genus Platanthera differ in their floral essences

Using the gas chromatography and mass spectrometry technique, they analyzed the aromatic essences of six different orchids. They were able to identify a quarantine of chemical products of the different species of orchids of the Plathantera genus, observing that Platanthera obtusata, unlike the others, has a large amount of a compound called nonanal, as well as small amounts of another compound, lilac aldehyde.

The researchers analyzed the reactions of different mosquito species (Aedes canadensis, Culsette sp., Aedes dianteaus and Aedes cinereus) to the identified chemical compounds, by recording the electrical activity of their antennas. Despite the fact that not all native Aedes species reacted with the same magnitude to chemicals, the responses were consistent, leading the team to examine whether other mosquitoes, not native to the orchid habitat, would react the same to their compounds chemicals.

They verified it with Anopheles stephensi, one of the species that spreads malaria and Aedes aegypti that spreads viruses of diseases such as dengue, yellow fever or Zika.

Both Aedes aegypti and Anopheles stephensi were attracted to the scent of orchids when lilac aldehydes were included. But by removing the lilac aldehyde from the aroma, both these species and the native Aedes lost interest in the flower or were repelled by the resulting odor.

Knowing how mosquitoes process complex odors to detect attractive food sources or others, as well as those odors that are repulsive to them could be used in the future to develop more effective repellents.


References:

Lahondère C, Vinauger C, Okubo RP, Wolf GH, Chan JK, Akbari OS, et al. The olfactory basis of orchid pollination by mosquitoes. Proc Natl Acad Sci USA. 2020;117:708–16

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