In a ground-breaking discovery encompassing six years of research, an international team of scientists led by UC Davis chemical ecologist Walter Leal announced they've identified the sex pheromone of the pest, which feeds on citrus and transmits the bacteria that causes the deadly citrus greening disease known as Huanglongbing (HLB).
Leal, a native of Brazil and a fellow of both the Entomological Society of America and the Entomological Society of Brazil, revealed the discovery during his presentation Dec. 5 at the 10th Annual Brazilian Meeting of Chemical Ecology in Sao Paulo. His team included scientists from UC Davis, University of Sao Paulo, and the Fund for Citrus Protection (FUNDECITRUS) from the state of Sao Paulo.
“Dr. Leal's discovery of the Asian citrus psyllid pheromone is a significant breakthrough in preventing the spread of this serious citrus insect, and may offer a less toxic method for its control,” said 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. He was not involved in the study.
“Having a lure to dramatically improve captures of this psyllid with the conventional sticky traps is a major progress toward integrated pest management,” said Professor Jose Robert Parra of the University of Sao Paulo.
Identifying the sex pheromone proved “complicated and quite a challenge” because of the insect's complex behavior and biology, said Leal, a UC Davis distinguished professor who has discovered the sex pheromones of moths, beetles, bugs, cockroaches, mites and other arthropods. A patent was filed Friday, Dec. 1, and journal publication is pending.
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.
Native to Asia, the Asian citrus psyllid, Diaphorina ciri, 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. The mottled brown insect, about 3 to 4 millimeters long, or about the size of an aphid, is now widespread throughout Southern California and is now found in 26 of the state's 58 counties.
The Asian citrus psyllid, or 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.
Currently growers are using yellow sticky traps to detect the insect and to monitor the population. “Efficient lures,” Leal said, “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.
Although ACP is present in Arizona and California, the disease itself has not been established, Leal said. “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.”
The detection of the pest has led to widespread eradication of citrus trees in China, Brazil and the United States. “In Brazil as many as 46.2 million citrus trees, representing 26 percent of the currently planted trees, have been eradicated since the detection of HLB in 2004,” Leal said. “In Florida, HLB has caused severe losses to the citrus industry. This year's production loss is estimated to be about 28 million fewer boxes of oranges than in 2014-2015.”
The announcement of the discovery coincides with the 40th anniversary celebration of FUNDECITRUS in Araraquara, Sao Paolo. “I am delighted that Walter Leal accepted our challenge to work on this project as the lead investigator,” said Juliano Ayres, FUNDECITRUS director. “The combination of his work ethics and qualifications are unparalleled. And, he loves challenges.”
In response to the ACP invasion in California, the California Department of Food and Agriculture (CDFA) has launched an extensive monitoring program to track the distribution of the insect and disease. They check yellow sticky traps in both residential areas and commercial citrus groves, and also test psyllids and leaf samples for the presence of the pathogen.
Survey methods for ACP include visual inspections, sweep netting, and placement of yellow sticky traps in trees in citrus nurseries, commercial citrus-producing areas and residential properties throughout the state, according to the CDFA. They also place sticky traps in California fruit packing houses, specialty markets, retail stores and airports that receive such produce from areas known to be infested with ACP.
Since August 2008, ACP has now been detected in 26 of California's 58 counties: Alameda, Contra Costa, Fresno, Imperial, Kern, Kings, Los Angeles, Madera, Merced, Monterey, Orange, Placer, Riverside, San Benito, San Bernardino, San Diego, San Joaquin, San Luis Obispo, San Mateo, Santa Barbara, Santa Clara, Solano, Stanislaus, Tulare, Ventura, and Yolo. “The ACP has the potential to establish itself throughout California wherever citrus is grown,” the CDFA says on its website.
CDFA has set up a hotline at 1-800-491-1899 for residents to report suspicious insects or disease symptoms in their citrus trees.
California Department of Food and Agriculture (CDFA)
Save Our Citrus: Hotline Information
UC Agriculture and Natural Resources (UC ANR)
In a groundbreaking discovery, a scientific team of Brazilians and Brazilian-born chemical ecologist Walter Leal of the University of California, Davis, has announced that the Zika virus has been detected in wild-caught Culex quinquefasciatus mosquitoes in Recife, the epicenter of the Zika epidemic.
Scientists from the Fiocruz Institute, Pernambuco, confirmed the discovery July 21. The detection could have widespread repercussions, as the Culex mosquitoes are more common and widespread than the yellow fever mosquito, Aedes aegypti, known as the primary carrier of the Zika virus.
Leal, who collaborates with Fiocruz Institute researcher Constancia Ayres in a National Institutes of Health-sponsored project on the investigation of Zika in the C. quinquefasciatus, said that the Brazilian lab earlier discovered that Culex had the capability of transmitting the virus. Although the scientists were able to infect the lab mosquitoes with the virus, they had not found the virus in wild-caught mosquitoes—until now.
“This could have major repercussions here in the United States and in other parts of the world,” said Leal, a distinguished professor in the UC Davis Department of Molecular and Cellular Biology who is co-chairing the International Congress of Entomology meeting Sept. 25-30 in Orlando, Fla. The conference is expected to draw some 7000 entomologists throughout the world.
Leal said more work needs to be done to see if Culex mosquitoes are playing a role in the current epidemic. In an interview July 21 with health reporter Jennifer Yang of the Toronto Star, Canada's largest daily, he commented: “It looks like there were more vectors than we thought, and this is one of them. We don't have to panic, but we have to know. And now that we know, we have to take care of the Culex.”
C. quinquefasciatus, known as the southern house mosquito and the vector of West Nile virus, thrives in temperate climates, including areas of California and the southern United States. In Brazil, it may be 20 times more common than A. aegypti, a day-biting mosquito that feeds primarily on humans. The mosquitoes differ widely: the yellow fever mosquito prefers urban environments and breeds in clean water, while the C. quinquefasciatus bites at night, breeds in dirty water and is commonly found in rural environments.
A. aegypti is already established in California; it has spread to at least seven counties since its discovery in Clovis, Fresno County, in June 2013, according to medical entomologist Anthony Cornel of the UC Davis Department of Entomology and Nematology and the UC Kearney Agricultural Research and Extension Center, Parlier.
The Zika virus, which can result in birth defects in pregnancy, can be transmitted through exposure to infected blood or sexual contact. The Centers for Disease Control estimates that between 400,000 and 1.3 million cases have been discovered across South, Central, and North America, where the disease was previously unknown.
Leal and a group of 18 students just hosted a Zika Public Awareness Symposium on May 26 at Giedt Hall, UC Davis campus. The podcast can be accessed at https://video.ucdavis.edu/media/Zika+Virus+Public+Awareness+Symposium/0_n3aupf5c
When chemical ecologist Walter Leal, professor of entomology at the University of California, Davis, was elected to the prestigious Brazilian Academy of Sciences, his lab members donned matching t-shirts--t-shirts with a touch of humor and a dose of humility.
On the front: "I did the work."
On the back: "And Walter Leal got in the Academy."
It was his idea and he purchased the t-shirts.
Leal, a native of Brazil, will be honored at a ceremony on May 7 in Rio de Janeiro.
“Let me say that your election to the Brazilian Academy of Sciences is a well-deserved recognition for your accomplishments as a distinguished scientist in your field of studies, entomology, and also for the very important role you have been playing in promoting cooperation among Brazilian and U.S .universities and, through those arrangements, fostering scientific development in our country,” said Ambassador Eduardo Prisco of the Brazilian Consulate in San Francisco.
Leal, a native of Brazil, is a liaison with UC Davis and the Brazil government’s Scientific Mobility Program, launched to exchange graduate and undergraduate students.
The U.S. currently hosts the largest number of students participating in the Brazil government’s Scientific Mobility Program, according to the Institute of International Education, and UC Davis leads the nation, hosting more than 30 Brazilian undergraduate scholarship students. Leal is also involved in the Brazilian/UC Davis student exchange with the Federal Agency for Support and Evaluation of Graduate Education (CAPES) and the National Council for Scientific and Technological Development (CNPq) grants for research related to Brazil.
A pioneer in the field of insect communication and on the cutting edge of research, Leal employs innovative approaches to insect olfaction problems. His work examines how insects detect smells, communicate with their species, detect host and non-host plants, and detect prey. Leal has designed and synthesized complex pheromones from many insects, including scarab beetles, true bugs, longhorn beetles and the citrus leafminer. He and his lab discovered the secret mode of the insect repellent DEET.
Leal, educated in Brazil and Japan, joined the UC Davis Department of Entomology in 2000. He holds a doctorate in applied biochemistry from Tsukuba University, Japan, and also earned degrees in chemical engineering and agricultural chemistry.
You'll be hearing much more of Walter Leal. Active in national and international entomological circles, the UC Davis professor is serving as co-chair of the International Congress of Entomology (ICE) conference, to be hosted by the Entomological Society of America (ESA) Sept. 25-30, 2016 in Orlando, Florida.
His honors and awards are many. He is a Fellow of the ESA, the Royal Entomological Society, and the American Association for the Advancement of Science. He served as president of the International Society of Chemical Ecology (ISCE). Among his awards: the ISCE Silver Medal, and awards from ESA and scientific societies in Japan and Brazil.
Caption (Top Photo):
The Walter Leal lab wore humorous t-shirts to announce his selection to the Brazilian Academy of Sciences. Four countries are represented in this lab photo. The four in front are (from left) Junior Specialist Hang Gao, United States; Professor Fen Zhu, Huazhong Agricultural University, China; Professor Leal, a native of Brazil; and Graduate Student Alyssa De La Rosa (Agricultural and Environmental Chemistry Graduate Group). Circling them in back are (from left) Postdoctoral Fellow Cherre Sade, Brazil; Postdoctoral Fellow Young-Moo Choo, Korea; Project Scientist Pingxi Xu, China; Graduate Student Kevin Cloonan (entomology major), Professor Carlos Ueira Vieira, Federal University of Uberlandia, Brazil; Graduate Student Yinliang Wang, Northeast Normal University, China; and Graduate Student Washington Carvalho, Federal University of Uberlandia.
Walter Leal isn’t participating in the Olympics, but he medaled just the same.
It was not for athletic prowess, but for scholarly achievements—the scientific equivalent of an international gold medal.
Leal, a chemical ecologist and a professor and former chair of the UC Davis Department of Entomology, is the recipient of the coveted Silver Medal, the highest award given by the International Society of Chemical Ecology (ISCE).
A native of Brazil and educated in Brazil and Japan, Leal researches how insects detect smells and communicate within their species. He is “one of the foremost authorities on the integration of chemical ecology with the molecular, biochemical and physiological interactions among insects and between insects and plants,” said chemical ecologist Coby Schal, professor at North Carolina State University, who nominated him for the award.
Bruce Hammock, UC Davis distinguished professor of entomology, wrote a letter of support, praising Leal for “his outstanding career achievements and excellence in moving chemical ecology forward." Hammock described him as “a world-renowned chemical ecologist, a pioneer in the field of insect olfaction, and on the cutting edge of research.”
ICSE president Paulo H. G. Zarvin of the Federal University of Parana, Brazil announced the award July 26 at the 28th annual ISCE annual meeting, held in Lithuania. It will be presented at the ISCE’s 29th annual meeting, set Aug. 19-22, 2013 in Melbourne, Australia.
Declaring Leal’s program, launched in 1990, as “one of the best in the world,” Schal lauded Leal as “one of the most energetic and collaborative scientists I know.”
“Chemical signaling is fundamental to all life forms, including microbes, plants and animals,” Schal said,” and chemical cues allow animals to appraise their environment; to detect food, toxins, prey, predators and pathogens; to identify kin; and to evaluate and base mate choice decisions of potential reproductive partners.”
“Walter’s research, in two decades, has addressed almost every aspect of chemical ecology,” Schal said. That includes “the semiochemistry of mites, thrips, scarabs, bugs, aphids, cockroaches, moths, wasps and plants.”
Leal, who joined the UC Davis faculty in 2000, has designed and synthesized complex pheromones from many insects, including scarab beetles, true bugs, longhorn beetles and the citrus leafminer. He identified the complex sex pheromone system of the naval orangeworm, a key agricultural pest responsible for multi-million crop damage annually in California. The sex pheromones he discovered are now being deployed in the agricultural field to disrupt chemical communication and control the navel orangeworm population through the environmentally friendly technique of mating disruption.
Leal and his lab discovered DEET’s mode of action, something that had puzzled and eluded scientists for half a century. Scientists long surmised that DEET, patented by the U.S. Army in 1946, works by masking the smell of the host, or jamming the insect’s senses, thus interfering with its ability to locate a host. Not so: in groundbreaking research published in the Proceedings of the National Academy of Sciences (PNAS), the Leal lab found that mosquitoes can indeed smell the chemical repellent but they dislike it so they avoid it.
Leal is one of only 23 scientists to receive the ISCE Silver Medal since its inception in 1986. Two other University of California scientists also won the award: Dave Wood of UC Berkeley in 2001 and Ring Cardé of UC Riverside in 2009.
Remember the exciting news article published in November of 2009 in Science Daily about how an orchid species on the Chinese island of Hainan "fools its hornet pollinator by issuing a chemical that honey bees use to send an alarm?"
The research was first published in Current Biology, a Cell Press publication.
"The discovery explains why the hornets, which capture honey bees to serve as food for their larvae, have been observed to literally pounce on the rewardless Dendrobium sinense flowers," the Science Daily author wrote.
Can you imagine? Hornets "detect" one of their favorite foods--honey bees--and they pounce on the flower and come up empty-handed or "empty-mouthed?"
The orchids produce a deceptive chemical, a compound called Z-11-eicosen-1-ol, described as "a rarity even in the insect world."
One of the researchers involved in this study--and hundreds of other insect communication studies--is world-renowned chemical ecologist Wittko Francke (top photo) of the University of Hamburg, Germany.
And now he's coming to the University of California, Davis, to present a seminar.
Francke will speak on "Insect Semiochemicals: Structural Principles and Evolution" at a UC Davis Department of Entomology seminar on Wednesday, Dec. 8 from 12:10 to 1 p.m. in 122 Briggs Hall, off Kleiber Hall Drive. He'll be introduced by host and fellow chemical ecologist Steve Seybold of the USDA Forest Service, Pacific Southwest Research Station, Davis, and an affiliate of the UC Davis Department of Entomology.
"Professor Francke has been a driving force in the field of chemical ecology for the last four decades, discovering countless new natural product chemicals of behavioral significance for animals and helping us to understand how plants and animals interact," said Seybold (left).
"Nearly everyone in the field has collaborated with him at some level; he has been a consummate mentor to younger chemical ecologists and has always been generous with his time, intellect, and chemical skills to everyone in that community," Seybold said. "He is remarkably brilliant in that he sees patterns in the make-up and synthesis of bio-organic compounds that most biologists, and even many chemists, may overlook."