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.”
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.)
Congratulations are in order.
Chemical ecologist Walter Leal, professor and former chair of the UC Davis Department of Entomology, has just been selected a Fellow of the Entomological Society of America, a prestigious honor granted to only 10 or few members of the 6000-member organization each year.
Leal is internationally known for his pioneering and innovative work on insect communication.
“This is a highly prestigious honor and richly deserved,” said Michael Parrella, professor and chair of the UC Davis Department of Entomology and one of 10 other UC Davis entomologists named ESA Fellows since 1947.
May Berenbaum, professor and head of the Department of Entomology, University of Illinois, Urbana-Champaign, one of the scientists who supported his nomination, praised him as a "trail blazer" and lauded his leadership.
Leal and his lab discovered the secret mode of DEET, the insect repellent. For some 50 years, scientists figured it worked by either jamming the insect's senses or masking the smell of the host. Not so. In groundbreaking research, the Leal lab showed that mosquitoes can indeed smell DEET, but they avoid it because they don't like the smell.
In other words, it smells bad. That's why they avoid it.
The groundbreaking research, published Aug. 18, 2008 in the Proceedings of the National Academy of Sciences, is among the most widely downloaded and cited PNAS documents.
Leal's pheromone work has graced the cover of several journals, including Structure, and has been showcased in the popular press, including the BBC, New York Times, and National Public Radio.
Leal has identified and synthesized complex pheromones from such insects as scarab beetles, true bugs, longhorn beetles, moths, and the naval orangeworm.
Entomologist Bruce Hammock, UC Davis distinguished professor of entomology, said Leal’s research has “practical implications in explaining how insects communicate within species, how they detect host and non-host plants, and how insect parasites detect their prey.”
Leal's navel orangeworm work alone is certain to result in a multi-million dollar beneficial impact on crops ranging from almonds to citrus, Hammock said. Leal's research on mosquito behavior is crucial to controlling vectorborne diseases like West Nile virus and malaria.
And now, an honor to match.
When UC Davis chemical ecologist Walter Leal received a major award from the Entomological Society of America at its 56th annual meeting, held in Reno, DEET has something to do with it.
Leal, who received the Recognition Award in Insect Physiology, Biochemistry and Toxicology from ESA president Michael Gray, has amassed an amazing record of productivity. Most recently: his lab discovered the mode of action for the mosquito repellent, DEET.
Contrary to previous hypotheses, DEET doesn't jam a mosquto's sense of smell or mask the smell of the host. The reason why mosquitoes avoid DEET is they don't like the smell and avoid it.
Leal, professor of entomology and former chair of the UC Davis Department of Entomology, was one of seven professionals receiving distinguished awards at the ESA meeting. The other categories were extension, entomology, horticultural entomology, teaching, the certification program, and early career innovation.
A pioneer in the field of insect olfaction, Leal is best known for his research on the mode of action of odorant–binding proteins and odorant-degrading enzymes on the identification and synthesis of insect sex pheromones and on insect chemical communication.
As colleague Ring Cardé, chair of the Department of Entomology at UC Riverside, said: "Dr. Leal is one of the leading scientists worldwide studying the chemistry of pheromone communication in insects and related arthropods.”