Mosquitoes that spread Zika, dengue and yellow fever are guided toward their victims by a scent from human skin. The exact composition of that scent has not been identified until now.
A UC Riverside-led team discovered that the combination of carbon dioxide plus two chemicals, 2-ketoglutaric and lactic acids, elicits a scent that causes a mosquito to locate and land on its victim. This chemical cocktail also encourages probing, the use of piercing mouthparts to find blood.
This chemical mixture appears to specifically attract female Aedes aegypti mosquitoes, vectors of Zika as well as chikungunya, dengue, and yellow fever viruses. This mosquito originated in Africa, but has spread to tropical and subtropical regions worldwide, including the U.S.
This new research finding, and how the team discovered it, is detailed in the journal Scientific Reports.
“Though others have identified compounds that attract mosquitoes, many of them don’t elicit a strong, rapid effect. This one does,” said Ring Cardé, UCR entomologist.
Mosquitoes use a variety of cues to locate their victims, including carbon dioxide, sight, temperature, and humidity. However, Cardé’s recent research shows skin odors are even more important for pinpointing a biting site.
“We demonstrated that mosquitoes land on visually indistinct targets imbued with these two odors, and these targets aren’t associated with heat or moisture,” Cardé said. “That leaves skin odor as the key guiding factor.”
Given the significance of odor in helping mosquitoes successfully feed on humans, Cardé wanted to discover the exact chemicals that make our scent so potent for the insects. Part of the equation, lactic acid, was identified as one chemical element in the odor cocktail as long ago as 1968.
Since then, several studies have identified that carbon dioxide combined with ammonia, and other chemicals produced by humans also attract these mosquitoes. However, Cardé, who has studied mosquitoes for 26 years, felt these other chemicals were not strong attractants.
“I suspected there was something undiscovered about the chemistry of odors luring the yellow fever mosquito,” Cardé said. “I wanted to nail down the exact blend.”
Methods that chemists typically use to identify these chemicals would not have worked for 2-ketoglutaric acid, Cardé said. Gas chromatography, which separates chemicals by their molecular weight and polarity, would have missed this acid.
“I think that these chemicals may not have been found before because of the complexity of the human odor profile and the minute amounts of these compounds present in sweat,” said chemist Jan Bello, formerly of UCR and now with insect pest control company Provivi.
Searching for mosquito attractors, Cardé turned to Bello, who extracted compounds from the sweat in his own feet. He filled his socks with glass beads and walked around with the beads in his socks for four hours per odor collection.
“Wearing the beads felt almost like a massage, like squeezing stress balls full of sand, but with your feet,” said Bello. ‘The most frustrating part of doing it for a long time is that they would get stuck in between your toes, so it would be uncomfortable after a while.”
The inconvenience was worth the investment. Bello isolated chemicals from the sweat deposited on the sock beads and observed the mosquitoes’ response to those chemicals. In this way, the most active combination emerged.
Future studies are planned to determine whether the same compound is effective for any other mosquitoes, and why there is such variation in how individuals are apt to be bitten. “Some are more attractive than others to these mosquitoes, but no one’s yet established why this is so,” Cardé said.
Though this discovery may not lead to insights for the development of new repellants, the research team is hopeful their discovery can be used to attract, trap, and potentially kill disease-spreading mosquitoes.
***Updated on Sept. 24, at 4 p.m.***
HONOLULU - Gene White, global director of vector management, Rentokil-Initial and one of the pest control industry’s leading educators and trainers, died Tuesday, in Honolulu. He was 64. White was in Honolulu attending the Society for Vector Ecology 2022 International Congress.
White’s more than 40 years in the pest control industry were mostly spent educating others, whether it was in various technical positions or speaking at industry conferences such as NPMA PestWorld or the Purdue Pest Management Conference.
White was a graduate student at Purdue University where he developed a special bond with Dr. Gary Bennett, retired professor and director of the Center for Urban and Industrial Pest Management at Purdue. The two were lifelong colleagues and friends who would go on outdoor adventures together. Bennett told PCT that Gene was “a special person who was unusually knowledgeable and more than willing to share his knowledge and experience with all who would listen. There is truly a part of me missing with the loss of Gene.”
Another industry professional impacted by White from his days at Purdue is Bobby Corrigan. The two would occasionally teach pesticide certification seminars together, which required them to travel together all week from one city to another. These were long drives that included sharing meals and hotel rooms. Corrigan recalled, “It is those trips that linger for me the most and are among my most treasured memories of Gene. Those times were typically filled with his contagious laughter because Gene loved to tell funny stories and to laugh. Over the years, I grew to learn that it gave Gene true pleasure to bring joy to other people’s days by making them smile and getting them to laugh.”
A native of the Akron, Ohio, area, White attended Glenville State College (W. Va.), where he graduated with a major in biology and minor in oral communications and was a member of the football team. He eventually found his way to Rose Pest Solutions, Troy, Mich., where he was hired to be a trainer. Among his accomplishments at Rose were helping to create an employee hiring template for technicians and the development and fine-tuning of training programs based on insect identification, which then led to the choice of products and treatment protocols.
At Rose Pest Solutons, White worked alongside Mark “Shep” Sheperdigian, vice president of technical services at Rose, who said he and White “meshed quite well in our abilities and interests.” The outgoing personalities shared a love of theater, which they tapped into to create radio clips and training videos, Sheperdigian recalled.
Sheperdigian said White was someone people naturally gravitated to. “He was always smiling, he was universally friendly and larger than life,” Sheperdigian said. “He was just a big happy guy and that attracted people.”
In 2013, White joined Rentokil North America, where he was hired as technical director for the Central Market, which spanned from Mexico to Canada. Four years later he was hired for the newly created position of global director of vector management for Rentokil-Initial, with responsibilities for creating and improving on the vector management space in the company.
Another reason White was so admired by colleagues was his infectious enthusiasm for entomology. He is remembered for his fun, interactive training sessions which extended into the community. For example, he led the outreach program “The Culinary Bugstitute,” which was part of the Cleveland Metroparks “Bug City” program for 23 years. He would spend a week creating a variety of insect dishes at his home in Michigan and then transport them to Cleveland (a 3-hour trip). In his 2018 Leadership profile, White recalled, “It was an absolute blast. I just had so much fun doing it and I think my enthusiasm helped, and I enjoyed coming up with new recipes. It was a great event to help promote the science of entomology.”
Dale Baker, vice president of sales J.T. Eaton and Pi Chi Omega member. said at his core White “was motivated to be of service. He loved to help people. He loved to educate people. He loved to talk to people. He loved to listen to people. He loved to learn from people. He loved people.”
Gene is survived by wife Janet and his children (Kyle and Karey) as well as Janet’s children (Chris, Kelly and Ryan). He was preceded in death by daughter Kelsey. Ceremony and memorial information were not available at this time.
A celebration of Gene's life will take place Sept. 30, starting at 2 p.m., at the South Lyon Hotel. Memorial donations may be given to Purdue University's Entomology Department. Click here for a link to his obituary.
The West Coast Rodent Academy will be held Nov. 2-5, at the University of California, South Coast Research and Extension Center, Irvine, Calif.
This event will be in person at the University of California, South Coast Research and Extension Center. This is the 14th West Coast Rodent Academy and the popular event has been strengthening since the first Academy back in 2016.
West Coast Rodent Academy co-organizer Niamh Quinn says. “Now that we have 13 events under our belt, the Academy is a pleasure to organize. The event itself is always such a wonderful experience where science, distribution, manufacturers, and the pest management professionals come together to learn about so many aspects of rodent management.”
The West Coast Rodent Academy is a three-day event that mixes time in the classroom with multiple hands-on activities. One of the most popular break-out sessions is the exclusion workshops where participants learn from industry professionals and have the opportunity to get their hands dirty learning the best management practices of exclusion.
This year’s principle partner is Bell Laboratories.