There are many ways to communicate with prospective romantic partners: If you are a Japanese scarab beetle, it's a matter of distinguishing left from right. New work from U.S. and Chinese scientists, published this week in Proceedings of the National Academy of Sciences, shows how these beetles use mirror-image pheromones to find a mate. The work could lead to better monitoring and control of significant agricultural pests.
The Japanese beetle, Popillia japonica, is a major agricultural pest that cannot be legally imported into the United States. In 1977, researchers discovered that females of P. japonica attract males with a pheromone, japonilure. Like most biological molecules, japonilure can exist in two forms that are mirror images of each other, the R-form and S-form. R-japonilure attracts males but S-japonilure repels them.
Twenty years later, Walter Leal, now professor of molecular and cellular biology at the University of California, Davis, and senior author on the new paper, discovered that a different, closely related scarab beetle, Anomala osakana, also uses japonilure as a sex pheromone, but the other way round: the S-form attracts males and the R-form repels them.
These species live in the same places, so it's likely that this system evolved to prevent mating attempts between the species, Leal said.
"This prevents them from wasting time and resources," Leal said.
How the beetles distinguish between forms of the pheromone that are identical apart from their handedness has been a long-standing mystery. Additionally, the Japanese beetles are difficult to study directly due to strict quarantines.
Swiping right or left
Leal and Chinese collaborators, including two former members of the laboratory at UC Davis, discovered a third beetle species that uses japonilure as a mating attractant. The copper green chafer, Anomala corpulenta, is another agricultural pest prevalent in southeast Asia and China.
The researchers discovered that in A. corpulenta, R-japonilure attracts males and S-japonilure has the opposite effect. They were able to show that the beetles have two key receptor genes, one of which responds to the R-form and another that responds to both forms and shuts down mating behavior.
Having discovered these receptors in A. corpulenta, the researchers then went looking for comparable genes in the genome of P. japonica, the highly quarantined Japanese scarab beetle. They identified two receptor genes, expressed the receptors in frog cells and showed that one responded strongly to R-japonilure while the other receptor acted as an antagonist.
The results show that these damaging pests all use a similar system to signal to potential mates while preventing fruitless interbreeding.
"The big goal is to use pheromones as tools to monitor and control populations of invasive beetles," Leal said.
In California, for example, detecting airborne pheromones could supplement traps and inspections as indicators of pests that have snuck aboard an airplane or ship. In places where the beetles are established, pheromones could be used to monitor populations and the breeding cycle. Finally, artificial pheromones might be used to disrupt mating.
Additional co-authors are: Yinliang Wang, Kun Feng, Huanhuan Dong, Kebin Li and Jiao Yin, Chinese Academy of Agricultural Sciences, Beijing; Haoqin Ke and Bingzhong Ren, Northeast Normal University, Changchun, China; Chen Luo, Yangzhou University, China; and Cheng Qu and Ran Wang, Beijing Academy of Agriculture and Forestry Sciences.
The work was supported in part by the National Key R&D Program of China, the National Natural Science Foundation of China and the Jilin Province Science and Technology Development Plan Item as well as various philanthropic gifts to UC Davis.
