Walter Leal and Team Identify Major Sex Pheromone of Severe Ag Pest

Newly published research led by UC Davis distinguished professor Walter Leal and  Jiao Yin of the Chinese Academy of Agricultural Sciences, Beijing, identifies the major sex pheromone receptor gene involved in the unusual 48-hour rhythm clock of the large black chafer beetle, a severe agricultural pest that targets such crops as peanuts, potatoes and soybeans in China, Japan, South Korea and India. 

The research, “Circabidian Rhythm of Sex Pheromone Reception in a Scarab Beetle,” published in the Jan. 18 edition of Current Biology, marks the first sex pheromone receptor identified in Coleoptera, the order of beetles. 

While most insects exhibit a 24-hour circadian rhythm that regulates their behavior and physiology, the large black chafer beetle, Holotrichia parallela, operates on a 48-hour clock, said Leal, a global expert on insect olfaction and communication.  A professor in the Department of Molecular and Cellular Biology, he is a former professor and chair of the UC Davis Department of Entomology, now the Department of Entomology and Nematology. 

“Insects smell with their antennae,” said Leal, who has unraveled the molecular mechanisms of mosquitoes, true bugs, long horned beetles, moths and other insects. “They have a sophisticated olfactory system and can selectively detect minute amounts of odorants.” 

The female H. parallela emerges from the soil every other night, after sunset, climbs the canopy of the host plant, and seeks a mate by releasing a sex pheromone. Leal wanted to know if the males are also on a 48-hour rhythm clock, and he wanted to identify the elusive male gene in the pheromone receptor that allows the male to scent the female's pheromone.

The answers: “yes” and “yes.” 

“I have been waiting for almost three decades to answer these questions,” Leal said. “I identified the sex pheromone of this beetle species in 1993 while working for the Ministry of Agriculture and Forestry of Japan. At that time, I found for the first time a very unusual sex pheromone, which is derived from an amino acid. Now similar sex pheromones have been identified from many species of beetles.” 

“Also, we showed that females produce the sex pheromone every other night,” Leal said. “The burning question in biology is what males do about sensing or smelling the female sex pheromone. Back then, we had no idea how insects sense smell. With the advancements in sequencing, we identified all potential receptors and identified which one senses the sex pheromone. COVID happened and delayed our research collaboration. Finally, we found that the receptor is expressed every other day.”

“This is remarkable,” Leal said. “How do they know when it is a 'date night' or a non-calling night? It is still a mystery, but we will find out one day.”  

Leal and Yin and their team pointed out that virtually all life on Earth experiences a 24-hour circadian rhythm, which affects almost all behaviors, including sexual activity and mating. 

“I love science that leverages rigorous molecular and cellular analysis to tell stories about fascinating natural history of species,” shared molecular geneticist and physiologist Joanna Chiu, chair of the UC Davis Department of Entomology and Nematology, in an email to the UC Davis News and Media Relations and the Department of Entomology and Nematology. “This study fits the bill. When Professor Leal first told me about the circabidian rhythm of pheromone release and reception in this scarab beetle, I was more than intrigued. Circadian rhythms (24-hour rhythms) in physiology and behavior are commonly observed in organisms, from bacteria to humans, but observations of circabidian rhythms (48-hour rhythms) in nature are rare. This elegant study by Professor Leal and his collaborators has provided us with an in-depth description of how the circabidian rhythm of pheromone detection in this beetle is generated. But like all good science, this study has now generated many more interesting questions that need to be answered.” 

Leal, a native of Brazil, received his Ph.D. in applied biochemistry from the University of Tsukuba, Japan, with subsequent postdoctoral training in entomology and chemical ecology at the National Institute of Sericultural and Entomological Science and Cornell University, respectively. He was the first non-Japanese person to earn tenure at Japan's Ministry of Agriculture, Forestry, and Fisheries. 

Leal, who joined the UC Davis faculty in 2000, is a newly elected trustee of the Royal Entomological Society, the first UC Davis scientist to be elected a trustee. He chaired the UC Davis Department of Entomology in 2006-2008 before accepting a position in 2008 as professor of biochemistry in the Department of Molecular and Cellular Biology.  His many honors include Fellow of the Entomological Society of America (2009), American Association for the Advancement of Science (2005), and the National Academy of Inventors (2019). 

Other co-authors of the Current Biology paper:  Yinliang Wang, Huanhuan Dong, Yafei Qu, Jianhui Qin, Kebin Li, Yazhong Cao and Shuai Zhang, Chinese Academy of Agricultural Sciences, Beijing; Yuxin Zhou and Bingzhong Ren, Northeast Normal University, Changchun, China; and Chen Luo, Beijing Academy of Agriculture and Forestry Sciences. 

The research drew financial support from the National Key R&D Foundation of China; National Natural Science Foundation, China; and the Natural Science Foundation of Beijing. 

Resources:

• For This Beetle, ‘Date Night' Comes Every Other Day, Jan. 18, 2024, Andy Fell, UC Davis News and Media Relations
• Walter Leal Elected Trustee of Royal Entomological Society, Sept. 5, 2023