[Photo] Sweetpotato whiteflies, Bemisia tabaci, feeding on a watermelon leaf. (Credit: USDA, Photo by Stephen Ausmus)

ScienceDaily (Nov. 15, 2007) ??? A population of the whitefly Bemisia tabaci has become one of the world's worst invasive pests -- devastating many crops in China and elsewhere in the process -- through mating behaviors that help it invade the territory of native whitefly populations, according to a new study conducted in China and Australia.

The researchers report that the invasive whiteflies are successful at least in part because they breed more when they come into contact with native whiteflies, and they also suppress the native whiteflies' reproduction rates.

The study demonstrates that behavior can play a critical role in animal invasions, the authors say. Understanding the invasion process is important for pest management, because it helps researchers make accurate estimates of how rapidly and to what extent an alien pest can be expected to invade and displace its native relatives.

The whitefly species, B. tabaci, consists of many different genetic groups or "biotypes." Biotype B, which probably originated in the Mediterranean-Asia Minor region and has spread through much of the world, is the one considered to be among the world's worst agricultural pests.

The insect reached Australia in the early 1990s and China in the mid-1990s, through the transport of ornamental and other plants. It affects many different types of crops, causing damage by feeding on plant leaves and spreading viral infections.

"The invasive pest reported in our paper is currently devastating China's agriculture and environment," said lead author Shu-Sheng Liu of Zhejiang University in Hangzhou, China. "As China's agriculture is more fragile than that of many developed countries, I expect the damage here will be much more severe and will continue for many years. I just returned from a three-day field trip, it was sad to see many tomato growers in Zhejiang are suffering complete loss of their entire crop this season due to this pest and the viruses it transmits,".

Dr. Liu and his colleagues conducted regular field sampling of whitefly populations in Zhejiang, China, from 2004 to 2006, and in Queensland, Australia, from 1995 to 2005, to monitor the B biotype whitefly behavior as it spread and displaced native whiteflies in the two regions.

They also conducted experimental population studies, simulating the displacement process on caged cotton plants. And, they developed a specialized video recording system to observe and analyze the insects' movement as well as the mating interactions between alien and native whiteflies on live plants.

The authors identified what they call an "asymmetry" in mating interactions between the invader and native whiteflies, whereby female biotype B whiteflies copulated with biotype B males more frequently when native whiteflies were also present. And, though male biotype B whiteflies didn't copulate with native females, they did court the native females, interfering with copulation between native males and females.

These findings will be published online by the journal Science, at the Science Express website, on 8 November, 2007.

"Asymmetric Mating Interactions Drive Widespread Invasion and Displacement in a Whitefly," by Shu-Sheng Liu, Jing Xu, Jun-Bo Luan, Lian-Sheng Zang and Yong-Ming Ruan of Zhejiang University In Hangzhou, China; P. J. De Barro of CSIRO Entomology in Indooropilly, Australia; and Fang-Hao Wan of the Chinese Academy of Agricultural Science, in Beijing, China. This study was supported by the National Basic Research and Development Program of China, National Natural Science Foundation of China, Ministry of Education of China, CSIRO Entomology, Horticulture Australia, and the Grains and Cotton Research and Development Corporations.