“I’m, um… just getting ready for my camping trip!”
Credit: © Anna Hoychuk, Shutterstock

Think of your favorite food. Imagine the cheesy or chocolaty or crispy delight. You might want to eat that food forever and ever. You might want to roll around in that food and change your name to that food. (Okay, maybe that’s a little too far.) But cats feel that strongly about a particular treat. They might not want to roll around in pizza or chocolate cake. But, they may want to roll around in their favorite herb: catnip. Catnip is a strong-smelling plant that many cats love to sniff. When exposed to catnip, a cat might rub its head and body on the herb, roll around in it, chew it, meow, and generally act crazier than usual. In addition, new research from Japan suggests that all that rolling around in catnip actually has health benefits for cats. Chemical compounds in catnip may help our feline friends ward off mosquitoes, pesky insects whose bites can transmit heartworm infections in cats.

The way in which scientists came to this conclusion may surprise you. No, researchers did not invite a dozen or so cats to a camping weekend. They did not give the cats supplies for feline-friendly s’mores—made with catnip and tuna sandwiched between kibble crackers. Researchers did not then examine whether mosquitos munched on cats while they told ghost stories around a campfire. No, none of this happened.

Instead, researchers gave some cats scraps of paper soaked with iridoid, a chemical in catnip that affects pleasure areas in the cat’s brain. The cats then rolled around in these slips of paper, reveling in the scientific process. Some cats did not receive these slips of paper. The researchers then placed the cats—both iridoid-perfumed and not—within reach of many mosquitoes. The mosquitoes bit the faces of the cats who had not received the iridoid-soaked paper. However, the mosquitoes did not bite the faces of the cats who had received the iridoid-soaked paper.

We know what you’re thinking: “Wait, if I rub some catnip on my body, will mosquitoes stay away from me?” And, unfortunately, the researchers don’t recommend that humans use catnip as a natural repellent (although it may help you attract the neighborhood kitties). In fact, researchers don’t even recommend that cats should use catnip as a natural repellent, until there is more evidence.

But, you can use catnip in other ways. Catnip has been cultivated for centuries and used for medicinal purposes. A tonic made from the plant is said to be a good remedy for colds. Catnip is also used as an herbal tea and provides a seasoning for cooking. So, if you can get your hands on some traditional human foods seasoned with catnip, enjoy! You will not have to share with mosquitoes. But, as for your cat, that might be a different story . . .

May 4, 2015

Genetic differences between humans help determine why mosquitoes appear to prefer the scent of some people over others, according to scientists at the London School of Hygiene and Tropical Medicine. The research may explain why some people can be eaten alive by mosquitoes while their companions remain untouched. The results were published last week in the online journal PLOS One.

Recent research shows that mosquitoes have preferences about which humans to feed upon based on genetic factors in humans. © Dmitry Knorre, Dreamstime

More than 3,000 species (kinds) of mosquitoes live worldwide. Only female mosquitoes bite, and only a few species attack humans. They sip the victim’s blood, which they need for the development of their eggs, usually leaving an itchy welt. However, certain mosquitoes spread some of the world’s worst diseases, including dengue, encephalitis, malaria, and yellow fever. Scientists know that mosquitoes locate their victims through smell, but they do not understand why some people are bitten more than others.

The London scientists observed 37 sets of twins in an experiment to test the attractiveness of skin odors to captive populations of Aedes aegypti, an aggressive species of mosquito known for its fondness for human blood. Each twin placed one hand into one side of a Y-shaped glass tube as 20 hungry mosquitoes were released into the far end of the tube. The shape of the tube allowed each mosquito to fly toward the hand with a scent they preferred and away from a hand they disliked. A screen prevented the mosquitoes from actually biting the subjects. The scientists ran 40 trials with each set of twins to determine if the mosquitoes favored one twin over another or if they favored or disliked both twins equally.

The scientists observed that the mosquitoes often had a clear preference or clear dislike of certain subjects. However, the experiments showed that the overlap in the mosquitoes preference or dislike was about double among identical twins than it was for fraternal twins. Since identical twins share 100 percent of their genetic makeup compared to fraternal twins, who share only about half their genetic makeup, the researchers determined a person’s degree of mosquito attractiveness is determined by their genes.

The experiment demonstrates that some people have genetic makeups that are more attractive to mosquitoes than others. In addition, scientists saw that some people also seemed to have genetic makeups that are naturally repellant to mosquitoes. The researchers know that genetic makeup has a role in a person’s individual body odor. However, many other factors, including diet and the billions of bacteria that make up a person’s microbiome (the microbes that live on and in a human body), contribute to that odor. The scientists hope to learn exactly what factors are responsible for skin odors that mosquitoes dislike in order to produce more effective mosquito repellants.

Other World Book articles:

• Gene
• Multiple birth

September 26, 2014

In an odd twist, Brazilian scientists from the Fundação Oswaldo Cruz (Fiocruz) Foundation and Brazil’s Ministry of Health are releasing thousands of specially modified mosquitoes in a region around Rio de Janeiro in an effort to reduce and perhaps even eliminate the spread of mosquito-borne dengue fever. For the program to work, the special mosquitoes must breed and eventually become the majority population in the region. By reducing the incidence of this debilitating mosquito-borne disease through natural methods, it may allow nations to reduce their widespread use of pesticides against mosquito populations. The release is the first of its kind to take place in a country in the Americas. Similar releases of specially-modified mosquitoes have been conducted in Australia, Vietnam and Indonesia.

Mosquites transmit a number of illnesses to humans, including dengue fever, malaria, and West Nile virus. (© Dmitry Knorre, Dreamstime)

Dengue fever, also called breakbone fever, causes headaches, eye aches, and severe pain in the muscles and joints, in addition to a high fever. It is caused by a virus transmitted only by mosquitoes of the species Aedes aegypti. Dengue is endemic (exists permanently) in Brazil and many other regions of the tropics and subtropics. Global health officials estimate that about 390 million people get dengue each year. Although it is seldom fatal, the debilitating illness is an enormous burden on the economy and health care systems of many developing countries. There is no known cure for the disease.

In a Brazilian laboratory, scientists from Oxitec, a British biotechnology corporation, infected Aedes mosquitoes with a parasitic microbe called Wolbachia. This common bacteria infects the cells of a mosquito, where it prevents the dengue virus from multiplying. The microbe acts like a vaccine against the dengue virus in the mosquitoes and, once infected with Wolbachia, the insects cannot transmit the disease to humans when they bite. Wolbachia also affects mosquito reproduction. Female mosquitoes usually mate only once in their lifetime. If a male mosquito infected with Wolbachia mates with an uninfected female, the eggs do not develop, reducing the entire mosquito population. When an infected female mates, her offspring will carry Wolbachia, ensuring future mosquito generations of her line will be immune to Dengue.

While it is impossible to eliminate all of the Aedes aegypti mosquitoes, scientists hope that surviving populations will be incapable of transmitting dengue to people. They believe it will take as long as 2 years to see if the program is effective. If successful, the mosquito program may also be used to help control other diseases transmitted through the bite of Aedes aegypti, including yellow fever or malaria.

Additional World Book articles:

• Blood Feeders: Real Life Vampires (a Special report)

• Overpopulation and the Threat of Disease (a Special report)

March 7, 2014

Warmer temperatures, associated with global warming, are causing malaria to become more common at higher altitudes, according to a report in the latest issue of the journal Science. A study of malaria in the highlands of Africa and South America by an international team of scientists found that generally higher temperatures in the future may well lead to millions of additional people exposed to the mosquito-borne disease.

Malaria, a disease common in tropical and subtropical regions, is caused by infection with parasites called Plasmodia. The parasites are one-celled organisms called protozoans. They are transmitted to human beings through the bite of the female Anopheles mosquito.

“The impact in terms of increasing the risk of exposure to disease is very large,” stated the lead author of the study, Mercedes Pascual of the University of Michigan. Pascual noted that in the past, higher altitudes provided  protection against this devastating disease because both the malaria parasite and the mosquito that carries it do not thrive in cooler air.

Malaria parasites appear in pink and blue in a false-color image. (c) CNRI/SPL from Photo Researchers

Pascual and her team studied densely populated areas in the highlands of Colombia and Ethiopia, where scientists have kept detailed records of both temperature and malaria cases from the 1990’s to 2005. The team found that malaria shifted higher into the mountains in warmer years and stayed at lower elevations in cooler years. “We have estimated that, based on the distribution of malaria with altitude, a 1-Celsius-degree (1.8-Fahrenheit-degree) rise in temperature could lead to an additional 3 million cases in people under 15 years old,” stated Pascual. Climatologists predict that Earth’s surface temperature could rise by as much as 1 Celsius degree by 2030.

The World Health Organization estimates that there were about 207 million cases of malaria in 2012 leading to approximately 627,000 deaths. Children living in Africa are particularly hard hit by the disease.

Additional World Book articles:

• Charles Louis Alphonse Laveran
• Sir Ronald Ross
• Blood Feeders: Real-Life Vampires (a Special Report)
• The Timeless Scourge of Malaria (a Special Report)

June 5, 2012

For a tiny mosquito, being hit by a fat raindrop should be roughly equivalent to a person being slammed by a bus. However, mosquitoes are struck by raindrops all the time–and they usually survive. The secret of their success? They ride the raindrop, says mechanical engineer David Hu of the Georgia Institute of Technology in Atlanta. Why is this important? The mosquito’s low mass may explain how they are able to survive in rainy, humid climates. And it reveals why a rainstorm offers little or no protection against the pesky bloodsuckers. Engineers may also find the mosquito’s survival technique useful for designing tiny robotic flying machines that can operate under harsh weather conditions.

A female mosquito feeds from a person using her needlelike mouth parts. Her abdomen has become swollen with red blood. A female must drink blood to nourish her eggs. (© Dmitry Knorre, Dreamstime)

For their study, Hu and his team put mosquitoes in cages that vibrated so the insects wouldn’t be able to land. Then they bombarded the bugs with rainstorm-like waterdrops that were 50 times as heavy as the mosquitoes and came at them at a speed of 30 feet (9 meters) per second. High-speed videos of the blitz revealed that the flying mosquitoes simply stuck to the droplets. In the process, they absorbed only 10 percent of the force of the droplet. The maneuver is an insect version of t’ai chi ch’uan, Hu said, in which one minimizes the force of an attacking opponent by not resisting. In contrast, droplets falling on mosquitoes sitting on a twig crushed the bugs with a force equal to 10,000 times the mosquito’s weight.

The hitchhiking insects tumbled for a distance of up to about 20 times their body length before flying off. The bugs’ water-resistant hairs likely aid in their escape. But the scientists found that low-flying mosquitoes ran the risk of running out of escape room, with the raindrops becoming watery coffins.