Breaking news and a well-deserved honor:

Insect chemical ecologist Walter Leal, a distinguished professor at the University of California Davis, has just been selected to deliver the Founders' Memorial Award Lecture at the Entomological Society of America (ESA) meeting, to be held Nov. 17-20 in St. Louis, Mo.

Leal, a distinguished professor in the Department of Molecular and Cellular Biology and a former chair of the Department of Entomology (now the Department of Entomology and Nematology), is known as a exemplary scientist, teacher and leader. He will discuss the work of insect chemical ecologist Thomas Eisner (1929-2011), widely known as "the father of chemical ecology."

Leal will present his talk, titled "Tom Eisner--An Incorrigible Entomophile and Innovator Par Excellence," at the Entomology 2019 awards breakfast, which begins at 7:30 on Tuesday, Nov. 19.

“I am absolutely delighted to have the opportunity to honor Tom Eisner--one of the founding fathers of chemical ecology,” Leal told us today. “And, consequently, Tom's main collaborator, the late Professor Jerry Meinwald--my role model, mentor and friend of three decades.”

Leal investigates the molecular basis of olfaction in insects and insect chemical communication. (See the Leal lab's work on DEET in Entomology Today.) He researches environmentally friendly alternatives to control insects of medical importance, and also targets agricultural pests.

Leal is the first UC Davis scientist selected to present the Founders' Memorial Lecture, although medical entomologist Shirley Luckhart of the University of Idaho, formerly of UC Davis, delivered the lecture in 2018. In her lecture, "He Gave to Man Control Over That Dreadful Scourge, Yellow Fever," she honored Walter Reed (1851-1902), the U.S. Army physician who in 1901 led a team of researchers that linked the spread of yellow fever to mosquitoes.

ESA established the Founders' Memorial Award  in 1958 to honor the memory of scientists who made outstanding contributions to entomology.

Thomas is known for his discoveries on chemical defenses used by insects against predators. “Notable among them was deciphering how the bombardier beetle defends itself with an internal exothermic chemical reaction, explosively sprayed at attackers,” according to a press release by Joe Rominiecki, ESA communications manager. “That discovery topped a lengthy list of revelations about the complex and often surprising biochemicals insects produce, from the bitter, predator-deterring taste of the cochineal scale's brilliant red pigment to the sticky foot secretions that allow the palmetto beetle to cling so tightly to leaf surfaces. “

Leal, whose career spans three decades, built his career on Eisner's work. Leal "has greatly advanced scientific understanding of insect olfaction," Rominiecki said.  "He has identified and synthesized several insect pheromones, and his collaborative efforts led to the first structure of an insect pheromone-binding protein." Leal's studies of olfaction in both agricultural pests and mosquitoes have also led to important management applications in the field. "His identification of the sex pheromone system in navel orangeworm (Amyelois transitella), for instance, has been deployed in agricultural fields via mating disruption, significantly reducing the need for pesticide sprays. And in 2018 Leal identified the sex pheromone of the Asian citrus psyllid (Diaphorina citri) a vector of citrus greening disease and a major threat to the citrus industry worldwide."

A native of Brazil and educated in Brazil and Japan, Leal received his master's degree and doctorate in Japan: his master's degree at Mie University in 1987, and his doctorate in applied biochemistry at Tsukuba University in 1990. Leal then conducted research for 10 years at Japan's National Institute of Sericultural and Entomological Science and the Japan Science and Technology Agency before joining the faculty of the UC Davis Department of Entomology in 2000.

Leal co-chaired the 2016 International Congress of Entomology (ICE), themed "Entomology Without Borders." The event, held in Orlando, Fla,. drew the largest delegation of scientists and experts in the history of the discipline. That would be 6682 attendees from 102 countries. 

Among his many honors, Leal is a fellow of three organizations--ESA, the American Association for the Advancement of Science,  and the California Academy of Sciences--and an honorary fellow of the Royal Entomological Society.  He received a silver medal from the International Society of Chemical Ecology. Another honor: he was inducted into the Brazilian Academy of Sciences.

“Walter is an amazing person and an amazing scientist,” said Fred Gould,  distinguished professor in the Department of Entomology and Plant Pathology at North Carolina State University. “His work has opened new doors to the understanding of how insects receive and perceive odors and has saved farmers in California and Brazil more than $100 million. He's at a point where he could sit back and bask in the glory of his accomplishments, but that is not Walter. He remains as prolific as ever.”

"Walter's lecture promises to be outstanding," said colleague James R. Carey, UC Davis distinguished professor of entomology and a fellow of ESA who received the organization's national distinguished teaching award. "He is known as one of the exceptional, truly elite, instructors at UC Davis and beyond."  Carey praised Leal's  "innovation in content delivery, engagement with his audience, his ability to inspire and motivate them, and his always-clever touches of humor."

ESA, founded in 1889, is the world's largest organization serving the professional and scientific needs of entomologists and people in related disciplines. Its members, now more than 7000, are affiliated with educational institutions, health agencies, private industry, and government. Headquartered in Annapolis, Maryland, the Society stands ready as a non-partisan scientific and educational resource for all insect-related topics.

The ESA meeting in St. Louis is expected to bring together approximately 3,000 insect scientists to share their latest research and communicate the global science of entomology, Rominiecki said.

Walter Leal

Frank Zalom

Three faculty members from the University of California, Davis, will be among those sharing the "people" spotlight at the joint meeting of the XXVII Brazilian Congress and X Latin American Congress of Entomology --and the spotted wing drosophila will be among the insects sharing the "insect" spotlight.

More than 2000 scientists are registered to attend the meeting, to be held Sept. 2-6 in Gramado, Brazil.

UC Davis scientists delivering plenary addresses will be Frank Zalom, distinguished professor of entomology, UC Davis Department of Entomology and Nematology and a past president of the Entomological Society of America (ESA); Walter Leal, distinguished professor, UC Davis Department of Molecular and Cellular Biology, and a past chair of the Department of Entomology and Nematology; and Joanna Chiu, associate professor and vice chair, UC Davis Department of Entomology and Nematology. More than 2000 attendees are registered.

On behalf of ESA, Zalom is co-organizing and co-chairing a joint conference with Antonio Panizzi, a past president and international delegate of the Entomological Society of Brazil. That event, to take place the day before the XXVII Congresso Brasileiro and X Congresso Latino-Americano meeting, will involve developing a “Grand Challenge Agenda for Entomology in South America.  

Zalom will speak on “The American Experience with the Grand Challenge Agenda in Entomology.” In addition, ESA president Michael Parrella, dean of the College of Agricultural and Life Sciences at the University of Idaho and a former chair of the UC Davis Department of Entomology and Nematology, will provide an update on the 2018 ESA annual meeting, set Nov. 11-14 in Vancouver, B. C. Speakers also will include the presidents of the entomological societies of Argentina, Peru and Brazil.

Leal, a native of Brazil, will present the opening lecture of the joint conference of the XXVII Brazilian Congress and X Latin American Congress of Entomology on “Insect Vectors: Science with Applications in Agriculture and Medicine,” on Sunday, Sept. 2. This will be his fourth opening lecture—a record—at the Brazilian Congresses of Entomology (2004 in Gramado; 2008 in Uberlandia; and 2014 in Goiania). As an aside, legendary entomologist Marcos Kogan previously held the record: he presented two opening lectures, one in 1983 and another in 2002. Both Leal and Kogan (professor emeritus of agricultural entomology, University of Illinois and professor emeritus, Oregon State University) were elected ESA fellows; Leal in 2009 and Kogan in 2016. Zalom received the honor in 2008.

Zalom, an integrated pest management specialist, and former director of the UC Statewide Integrated Pest Management Program (UC IPM) and Chiu, who specializes in molecular genetics of animal behavior, will speak on their research at the joint meeting. Zalom will deliver a plenary address on “Drosophila suzukii in the United States” on Sept. 5, and Chiu will keynote a symposium on Sept. 3; her lecture is titled  “Circadian Clock Research Applied to Agriculture and Public Health.”  She will give a second lecture: "Drosophila as an Insect Model" on Sept. 3.

The spotted wing drosophila (SWD) is a serious pest of fruit crops. Most drosophila flies feed on spoiled fruits, but SWD prefers fresh fruit (berries and soft-skinned fruits). Read more about SWD on the UC IPM website.

A major citrus pest may experience a “Bah, Humbug!” kind of year.

If all goes as planned, UC Davis chemical ecologist Walter Leal's discovery of the sex pheromone of the Asian citrus psyllid--which spreads the deadly citrus greening disease, Huanglongbing (HLB)--may result in the insect version of “The Fatal Attraction.”

“We are now working on a formulation to be used in traps,” Walter Leal said this week. “This might take a year, but hopefully will be ready before the flight season in California.”

Leal, who led an international team of scientists in the six-year research project, announced the discovery Dec. 5 at the 10th Annual Brazilian Meeting of Chemical Ecology in Sao Paulo. Leal is a native of Brazil and a fellow of both the Entomological Society of America and the Entomological Society of Brazil.

“The Asian citrus psyllid (ACP) is a major threat to the multibillion dollar citrus industry in the United States,” said UC Cooperative Extension advisor Surendra Dara of San Luis Obispo and Santa Barbara counties. “When an insect pest vectors a deadly disease, the threat is more serious and ACP being an invasive pest made its management even more challenging.  Discovery of a sex pheromone by Dr. Leal's team is a major breakthrough not just for managing a dangerous invasive pest, but also a significant contribution to environmental sustainability.  I envision this pheromone becoming a clean, green, mean weapon in the IPM arsenal against ACP.”

The citrus greening disease, which has wreaked havoc in Florida, now threatens the California citrus industry. The mottled brown insect, Diaphorina citri, is now found in 26 of the state's 58 counties, but the disease itself has not been established.

Joel Nelsen, president of the California Citrus Mutual, called the discovery “exciting news” and a “first step toward protecting the citrus industry. We're hoping that the next steps come in time to protect thousands of citrus growers around the country.”

“Let's move forward fast and furious,” he said, noting that the citrus industry spends millions to support the research community.

The Leal-led research team was funded solely by Fund for Citrus Protection (FUNDECITRUS).

Integrated pest management specialist Frank Zalom, distinguished professor with the UC Davis Department of Entomology and Nematology and a past president of the Entomological Society of America, hailed the discovery as a “significant breakthrough in preventing the spread of this serious citrus insect, and may offer a less toxic method for its control.” He was not involved in the study. 

Kris Godfrey, associate project scientist at the UC Davis Contained Research Facility and formerly with the California Department of Food and Agriculture, agrees that better detection traps are needed. “I hope that Dr. Leal's discovery of an Asian citrus psyllid pheromone will provide the improvement in detection trapping that is needed by anyone trying to manage this insect and slow the spread of huanglongbing, a devastating disease of citrus vectored by the Asian citrus psyllid.”

Leal's Brazilian liaison, Haroldo Xavier Linhares Volpe of the Fund for Citrus Protection (FUNDECITRUS) from the state of Sao Paulo, pointed out that the discovery could “increase the ACP catches using lures with the attractive compound, leading to a more assertive, precise monitoring and could promote an early detection of ACP.”

“With a more accurate detection, we can adopt ACP integrated pest management (IPM) tools as soon as possible, avoiding or minimizing HLB spread.” He added that the lures should help decrease the population.

“However, researchers need to test all the management strategies before they are adopted,” Volpe said. “Formulation techniques need to be investigated to determine lures that release the compounds for a long time and at doses that attract the insect.”

Although ACP is present in California, the disease itself has not been established, Leal emphasized. “The emphasis is on detection, eradication and limiting the spread of the disease. In Florida, where HLB is widespread, monitoring ACP populations is essential to avoid reinfection after eradication of infected plants.” California now leads the nation in citrus production, surpassing Florida, for the first time in 70 years.

Currently growers are using yellow sticky traps to detect the insect and to monitor the population. Said Leal: “Efficient lures are sorely needed for sticky traps, particularly for early ACP detection. Otherwise, growers have to resort to regular sprays to avoid infection given that infected insects from gardens and noncommercial areas migrate to citrus farms.”

Pheromones and other semiochemicals are widely used in agriculture and medical entomology. “Growers use them as lures in trapping systems for monitoring and surveillance, as well as for strategies for controlling populations, such as mating disruption and attraction-and-kill systems,” Leal noted.

ACP feeds on new leaf growth of oranges, lemons, mandarins, grapefruit and other citrus, as well as some related plants. Infected psyllids can transmit the bacterium Candidatus Liberibacter asiaticus, which causes the fatal citrus disease. An early symptom of HLB in citrus is the yellowing of leaves on an individual limb or in a sector of a tree's canopy.

Native to Asia, ACP was first detected in the United States in June 1998 in Palm Beach County, Florida, and in California in August 2008 in San Diego County. Scientists discovered HLB in Florida in August 2005, and in Los Angeles in March 2012. 

Citrus trees infected with HLB usually die within five years, according to the UC Statewide Integrated Pest Management Program. There is no known cure. “The only way to protect trees is to prevent spread of the HLB pathogen in the first place, by controlling psyllid populations and removing and destroying any infected trees,” UC IPM says on its website.

(Editor's Note: The research was published in the Jan. 11 edition of the journal Scientific Reports.)

Listen to ABC Channel 10 News, broadcast Dec. 22
Seventeen-year-old Helena Leal doesn't like mosquitoes, but they like her.

“I always get bitten by mosquitoes more often than my family and friends,” says the Davis High School senior. “I get fairly bad reactions to mosquito bites, including swelling and itching, so I always have to be meticulous in using repellents.”

Thanks to her lifelong interest in those pesky female mosquitoes that target her for a free (blood) meal, Helena Leal now joins the ranks of published scientists. She's the lead author of UC Davis-based research published Dec. 21 in the journal Nature Scientific Reports. 

“It was great to have the opportunity to do research addressing a question I've had ever since I was a child,” she said of the work, “Attraction of Culex Mosquitoes to Aldehydes from Human Emanations,” completed in the UC Davis Department of Molecular and Cellular Biology lab of her father, chemical ecologist Walter Leal. In addition to the father-daughter team, co-authors are UC Davis student researchers Justin K. Hwang and Kaiming Tan of the Leal lab. 

Aldehydes are organic compounds—many fragrances are aldehydes—while skin emanations are odorants.

“Helena has always been curious about mosquito bites,” said her father, a distinguished professor who unravels the molecular mechanisms that make the olfactory system of insects so sensitive and selective. “Her research suggests that some people attract more mosquitoes—and receive more bites—because of their ratio of aldehydes, not because of natural repellents. We all produce these aldehydes but their ratios differ from person to person. The previous hypothesis is that people attract more mosquitoes because they lack a natural repellent. We found that the natural repellent is not produced in enough amount to repel.”

 “Our paper shows that the aldehyde ratio is very important,” Helena said. The researchers studied the southern house mosquito, Culex quinquefasciatus. Female mosquitoes feed on humans and other vertebrates to acquire nutrients to develop their eggs, she noted. Infected mosquitoes can transmit such viruses as West Nile, Zika and the St. Louis encephalitis virus.

 “The public has a genuine interest in understanding how mosquitoes find their hosts,” Helena wrote. “A Google search at the time of this writing, for example, produced almost 15 million results for the questions ‘why do mosquitoes find me?' Likewise, the question ‘why do mosquitoes prefer one person and not another?' generated more than 13 million results.”

 An article in the July 13, 2013 edition of the Smithsonian magazine related that an estimated 20 percent of people “are especially delicious for mosquitoes and get bit more often on a consistent basis.”

Regardless of the public interest, mosquitoes find their hosts by physical and visual cues, the researchers related. This can include heat and moisture, but more importantly, odorants.

Various factors contribute to differential attraction, including pregnancy, malaria infection, alcohol/beer consumption, skin microbiota, genetic makeup, and even blood type.

Fellow researcher Kaiming Tan said he was "delighted to see Helena able to facilitate her learning in a laboratory setting with a team of university students at UC Davis, a world-class research institution." He praised her interests in asking scientific questions, leading to solutions, as "useful skills in her future education endeavors."

"Dr. Leal's continuing support and mentoring on this student-run research project motivate us to pursue our goals," Tan added. "It is my pleasure to be on this team and pass down my knowledge to the next generation of college students."

Almost a century ago scientists identified carbon dioxide CO₂ as a primary mosquito attractant, and it's commonly used to trap bloodseeking female mosquitoes. “However, no evidence is available that suggests that CO₂ mediates differential attraction, i.e., carbon dioxide emission levels do not explain the common observation that mosquitoes systematically prefer one person to another,” the research team wrote. They agreed that skin emanations “play a key role in the mosquito finding a host” and that “these emanations are complex in nature and contain hundreds of compounds, but as far as mosquitoes are concerned, a handful of compounds activate the mosquito's olfactory system.”

“Anecdotes related to preferential mosquito bites are very common, but to date there is no complete explanation as to why one out of two people systematically receives more mosquito bites than the other when both are equally accessible,” the researchers wrote in their abstract. They tested the hypothesis that two constituents of skin emanations, 6-methyl-5-heptan-2-one (6MHO) and geranylacetone (GA), are natural repellents and may account for differential attraction in different ratios. “We studied skin emanations from two human subjects, confirmed in behavioral assays that female southern house mosquitoes are significantly more attracted to subject A (attractant) than to subject N (nonattractant), and tested their 6MHO/ GA ratios 2/23 in a dual-choice olfactometer.”

“Although repelling at high doses, 6MHO/GA mixtures were not active at the levels emitted by human skin,” they wrote. “We found, however, differential attraction elicited by the aldehydes in the ratios produced by subjects A and N. When tested in a dose commensurate with the level released from human skin and in the ratio produced by subject A, the aldehyde mixture significantly attracted mosquitoes. By contrast, an aldehyde mixture at the same ratio released by subject N did not attract mosquitoes. We, therefore, hypothesized that aldehydes may play a role in the commonly observed differential attraction.”

Helena worked on the project during the summer and into the fall. The Davis High School scholar recently received a scholarship from the Mexican-American Yolo County Concilio at its recognition dinner and scholarship fundraiser. She told the crowd that she plans to major in cognitive science with a focus on artificial intelligence.

Her other interests? "I play lacrosse and tennis on my school teams, but I also love to dance. I currently spend a lot of time working on the school yearbook as an editor. I am a big fan of live music and I am learning how to play the guitar."

Her brother, Gabriel, now 20, also did research in the Leal lab and saw his work on the odorant-binding protein of the yellow mosquito published.  In addition, Gabriel worked on almond research (unpublished). Now a student at Dartmouth, Gabriel is majoring in economics and minoring in engineering and philosophy. Older brother Augusto, 26, holds a degree in political sciences from Princeton University with a minor in economics.

The Leal lab is “particularly interested in elucidating the roles of odorant-binding proteins, odorant receptors, and odorant-degrading enzymes,” said Leal, adding that “Insects are extremely successful animals whose lives intertwine with ours. They may be vegetarian and harmful to our food supply as well as vectors of pathogens that inflict tremendous suffering and human loses. Thus, a better understanding of the molecular basis of insect olfaction may facilitate the design of eco-friendly chemicals to controls insects of medical and agricultural importance.”

The Leal lab is credited with discovering the exact mode of action of DEET, “the gold standard” of insect repellents for the past six decades. “DEET doesn't mask the smell of the host or jam the insect's senses,” Leal said. “Mosquitoes don't like it because it smells bad to them. That's why they avoid it.” The also discovered the DEET receptor, which is also sensitive to plant defense compounds. 

“It's interesting what will repel and what will attract mosquitoes,” said Helena Leal. “It appears that mosquitoes will always find me--and 20 percent of the rest of the population—as especially delicious. They're out for blood—our blood. Let's keep them at bay with repellents.”

(Editor's Note: Walter Leal is a fellow of the Entomological Society of America and former chair of the UC Davis Department of Entomology and Nematology.)