By Kathy Keatley Garvey
Rice farmers seeking to protect their crops from pests but without the high dependency of pesticides may want to consider the sustainable pest management practice known as the “banker plant system.”
First-of-its-kind research, published in Scientific Reports of the journal Nature by a nine-member team, including UC Davis agricultural entomologist Christian Nansen, indicated that attracting alternative hosts to parasitoids of rice insect pests, can help protect a rice crop. The players: a grass species, a planthopper, and an egg parasitoid.
The field and laboratory work, done in China, targeted the brown planthopper, Nilaparvata lugens, or BPH, the economically most important rice pest in Asia. Results showed that BPH densities were “significantly lower in the rice fields with the banker plant system compared to control rice fields without banker plant system,” the scientists said.
“Many people are familiar with the concept of a ‘trap crop'-- a sacrificial crop which is planted mixed in with or adjacent to an economically important crop and the trap crop serves to manipulate pests away by offering them a more attractive/suitable host alternative,” said Nansen, an assistant professor with the UC Davis Department of Entomology and Nematology. “The use of banker plants in pest management is similar to the use of trap crops, but banker plants typically have multiple ecological functions.”
The researchers planted a grass species, Leersia sayanuka, next to rice. It attracted a planthopper (Nilaparvata muiri), which does not infest rice.
“But N. muiri is a very good host for the important egg parasitoid, Anagrus nilaparvatae, which is also a parasitoid of the economically important pest, the brown planthopper, Nilaparvata lugens,” Nansen explained. “So, by planting the grass, the parasitoids have plenty of hosts year round – even after the rice harvest season– and that ensures steady population dynamics of the parasitoid across seasons.”
Rice is the stable food of more than 50 percent of the global population, and 60 percent of the Chinese population. However, scientists concur that the world's rice production needs to increase drastically over the next three decades to meet the growing food demand in Asia. Growing concern over BPH outbreaks and higher pesticide usage led to the sustainable pest management study.
Titled “Use of Banker Plant System for Sustainable Management of the Most Important Insect Pest in Rice Fields in China,” the research is unique in that it is the first published study describing the attraction of alternative hosts to parasitoids of rice insect pests. In rice systems, previously published research involved planting sesame as a nectar source to promote the establishment and persistence of a predatory bug; and studies involving parasitoids.
BPH, found only in southeast Asia and Australia, feeds on the rice crop at all stages of plant growth and can also transmit two viruses, rice ragged stunt virus, and rice grassy stunt virus. Damage can commonly result in a 60 percent yield loss. An infestation is often called “hopper burn,” referring to yellow patches that soon turn brown.
Although BPH is not found in the United States, this kind of study “may be an approach to consider in California in the future if insecticide resistance continues to impeded effective insect control,” Nansen said.
Noting the importance of the banker plant system, Nansen said that banker plants “involve promotion of plant diversity to enhance pest self-regulatory ecosystem functions, such as predation and competition, to reduce susceptibility of agricultural crops to native and invasive pests. Also, banker plants “may provide resources, such as shelter, pollen and nectar or alternative preys to improve the establishment and persistence of beneficial insect populations used to control a specific pest.”
The first successful banker plant system, developed in 1977, involved tomato as the banker plant, a parasitoid and a whitefly.
Nansen is affiliated with both UC Davis and the Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection and Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China.
Co-authors of the research paper include lead author Zhongxian Lu and colleagues Xusong Zheng, Yanhui Lu, Junce Tian, Hongxing Xu, all of the Zhejiang Sustainable Pest and Disease Control; and Pingyang Zhu, Facheng Zhang and Guihua Chen of the Jinhua (China) Plant Protection Station.
The study was jointly supported by the National Key Research and Development Program of China, Zhejiang Key Research and Development Program, and the Special Fund for Agro-scientific Research in the Public Interest.