Why Mosquitoes Prefer Some Individuals Over Others

Scientific evidence has demonstrated that mosquitoes are more attracted to certain individuals than others, and this phenomenon is partly influenced by genetic factors. To support this claim, this video is sponsored by 23andMe, a company specializing in analyzing sections of your genetic code to provide insights about your genetic makeup. In fact, 23andMe has been involved in research that has identified specific genetic markers that make individuals more or less attractive to mosquitoes.

To put this theory to the test, the video crew traveled to New Mexico State University to meet with Professor Immo Hansen, renowned as the "mosquito man." At the university, Professor Hansen maintains colonies of various mosquito species, including an exotic strain that he personally nourishes with his own blood. Surprisingly, these particular mosquitoes are bred using his blood exclusively.

Curious about the process, the video host inquired about how Professor Hansen feeds the mosquitoes with his blood. The professor humorously confirmed that he indeed feeds them himself and, due to the logistical challenges of obtaining permissions, he is the sole provider of blood meals. Professor Hansen simply places his arm in the container and waits for the mosquitoes to feed on him, emphasizing that it can be quite itchy.

The video host learned that only female mosquitoes require blood proteins to develop their eggs. Mosquito eggs hatch into larvae, which then progress through the pupal stage before maturing into adult mosquitoes. Once mature, the female mosquitoes once again seek out vertebrate blood to lay more eggs. The entire mosquito lifecycle from egg to adult takes only two weeks. Intrigued, the host wanted to determine whether they were an attractive target for mosquitoes.

To assess their attractiveness to mosquitoes, the host was introduced to a Y-tube apparatus with two chambers. Mosquitoes were placed in a holding chamber at the base of the apparatus. By creating a draft with a small fan, a flow of air at approximately 4 m/s was induced through the chambers. The host's hand was to be placed in either the green or yellow chamber as the "bait."

Realizing that they were the bait, the host jokingly confirmed with Professor Hansen that it would be beneficial to rub their hand first to release any oils or sweat. The professor explained that these substances attract mosquitoes, especially in the desired location. The video host then positioned their hand accordingly, preparing for the experiment.

Professor Hansen explained that the particular mosquito species in question predominantly feeds on humans and is highly specialized in this regard. Amused by this information, the host commented on their newfound knowledge. After releasing 20 mosquitoes into the holding chamber, the video host observed the insects making their choices.

Excitedly, the host noted that one mosquito had chosen incorrectly and was left behind. Professor Hansen acknowledged this and exclaimed that the host was indeed attractive to mosquitoes. All the released mosquitoes had flown in the direction of the host's hand, while none ventured to the other side of the apparatus.

Overwhelmed by the outcome, the host expressed surprise at the strong response, with multiple mosquitoes gravitating towards them. This experiment, similar to others conducted previously, aimed to investigate the genetic basis of mosquito attractiveness. In a previous study, 18 pairs of identical female twins and 19 pairs of fraternal female twins were recruited. Using the Y-tube Test, researchers assessed the mosquito attractiveness of each individual by determining the fraction of mosquitoes that flew correctly towards the arm of the tube where the twin was standing.

The study revealed a correlation between the mosquito attractiveness of twins, indicating that if one twin was highly attractive to mosquitoes, the other twin was also likely to be attractive. While this finding may not be surprising and could be influenced by shared environmental factors or diet, a comparison between identical and fraternal twins showed a stronger correlation among identical twins.

In summary, scientific research has shown that mosquitoes are more attracted to certain individuals than others, and genetic factors play a significant role in this attraction. The video showcased an experiment confirming the host's strong attractiveness to mosquitoes, while also highlighting previous studies that demonstrate the correlation between mosquito attractiveness among twins, particularly identical twins.

This strongly indicates that genetics play a role in determining an individual's attractiveness to mosquitoes. Since identical twins share more of the same genes compared to fraternal twins, it explains why the correlation in mosquito attractiveness is higher among identical twins if genetics indeed influence how much mosquitoes are drawn to a person.

Reflecting on the previous experiment where the host was attractive to mosquitoes, they noted that the comparison was made to a control with no human present. However, they proposed a new test to compare their attractiveness to mosquitoes with their wife, Raquel. The host humorously mentioned that while they typically get bitten by mosquitoes, Raquel does not. They were curious to see if this anecdotal finding would be replicated under controlled laboratory conditions.

With hands in position, the host and Raquel prepared for the test. Professor Hansen observed that the mosquitoes started to show activity, indicating their awareness of something happening. The experiment commenced, and both individuals experienced mosquito bites. The host believed they were receiving more bites, while Raquel had fewer. Professor Hansen decided to halt the experiment to evaluate the results.

After counting the mosquitoes, it was evident that the host had received more bites. Although the test lacked scientific rigor, it replicated their real-world experience that the host was more attractive to mosquitoes than Raquel. This led to the question of whether genetics played a role in their differing attractiveness.

To explore this further, the couple provided saliva samples that were sent for testing. They were particularly interested in seven specific locations on their DNA, identified in a 2017 study conducted in collaboration with 23andMe. Through the study, 16,000 participants rated their perceived attractiveness to mosquitoes, and a genome-wide association study was performed to analyze the DNA of those who reported being attractive or unattractive to mosquitoes.

Upon receiving the results, the couple discovered that they shared the identical DNA at four of the seven locations related to mosquito attractiveness. This ruled out those areas as contributing factors. However, they found differing DNA at three locations. At the first location, Raquel had a protective genetic variant that made her significantly less attractive to mosquitoes, while the host did not possess any changes at that site.

At the second location, the host had a genetic change that made them less attractive to mosquitoes, offering some level of protection. In terms of significance, Raquel's genetic change was approximately twice as significant as the host's change. Nevertheless, both individuals exhibited protective genetic variants. The last location where they differed significantly revealed that the host had two copies of a variant associated with increased mosquito attractiveness, whereas Raquel had none.

Overall, their genetic analysis aligned with their experiences. While it doesn't provide definitive proof, it is consistent with the idea that these specific genetic variants are associated with mosquito attractiveness. They acknowledged the complexity of understanding how these genetic changes precisely influence an individual's attractiveness to mosquitoes.

However, the specific mechanisms behind mosquito attraction are not yet fully understood. It is likely related to the odors or volatile chemicals emitted by our bodies, as well as the influence of our skin's microbiome. One of the key signals that mosquitoes are drawn to is carbon dioxide. This means that individuals with a higher metabolism, those who have recently exercised, larger individuals, and even pregnant women are more likely to attract mosquitoes. Mosquitoes are also attracted to other volatile compounds we release, such as lactic acid, acetone, and ammonia.

On the other hand, scientists have discovered certain chemicals that repel or interfere with mosquitoes' ability to locate us. These natural repellents include octanal, nonanal, decanal, and 6-methyl-5-hepten-2-one. Understanding these factors is crucial because researchers estimate that our attractiveness to mosquitoes is as hereditary as traits like height or IQ. Therefore, genetics play a significant role, which is especially important when considering that mosquitoes have the greatest impact on human health compared to any other animal.

In fact, mosquitoes are considered the most dangerous animal in the world. Diseases transmitted by mosquitoes, such as malaria, have claimed the lives of millions of people throughout history. While estimates may vary, mosquito-borne illnesses continue to cause significant mortality rates, with over a million deaths per year. This led to the question of whether humans may have evolved to smell less appealing to mosquitoes as an adaptation to avoid these diseases or if it is merely coincidental that some people are less attractive to mosquitoes than others.

Considering evolution, an intriguing fact is that malaria, when contracted, alters the host's body chemistry to produce an odor that makes them more attractive to mosquitoes. The malaria parasite has evolved this ability despite mosquitoes being the carriers of the disease. It is truly remarkable how evolution shapes these interactions.

Although the availability of a mosquito attractiveness test is not currently offered by 23andMe, the company focuses on helping individuals understand the information encoded in their chromosomes. While physical traits, health aspects, and ancestry information are accessible, the specific genetic factors influencing mosquito attractiveness are not yet included. The host then shared their personal 23andMe results, showing a diverse genetic heritage, with a significant European background and a surprise South Asian ancestry.

In conclusion, while the precise mechanisms of mosquito attraction are not fully known, it is likely influenced by our body odors, volatile chemicals, and genetic factors. Mosquitoes' impact on human health underscores the importance of understanding this relationship. The intricate coevolution between mosquitoes and diseases like malaria further exemplifies the fascinating nature of evolution.