Whitefly, one of the world's most invasive agricultural pests that has devastated crops in China and Australia in recent years, owes its "success" to its mating habits, said a leading Chinese entomologist Friday.
Liu Shusheng, an expert at the Insect Sciences Institute under China's Zhejiang University in Hangzhou, and Paul De Barro, a scientist at CSIRO Entomology, Australia's national science agency in Brisbane, have jointly published a paper on their research in the latest Science Journal published by AAAS.
The scientists conducted regular field samplings of whiteflies in east China's Zhejiang Province between 2004 and 2006 and in Queensland, Australia, from 1995 to 2005 to monitor the insect's behaviour.
The insect arrived in Australia and China in the 1990s through the international flower trade and has since displaced native populations of the same type of whitefly in both countries.
In Zhejiang, for example, it took the invaders just three to five years to supplant the native population, according to the research.
"The invasive pest reported in our paper is currently devastating China's agriculture and environment," said Liu, lead author of the study.
The marauding aphids have blighted tomato and vegetable crops and in some cases spread plant viruses, forcing farmers to spend millions extra for additional insecticide supplies.
"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," said Lui, who recently returned from a three-day field trip.
"It was sad to see that many tomato growers in Zhejiang are suffering complete losses of their entire crop this season due to this pest and the viruses it transmits." But the invasion also intrigued entomologists who wondered how this member of the silverleaf whitefly Bemisia tabaci species -- a genetic variant known as Biotype B -- could so quickly establish its dominance in a new territory.
"We're trying to find out what made B. tabaci biotype B such a successful invader and the answer appears to be sex," said Liu.
The scientists found what they called an "asymmetry" in mating interactions between the invader and native whiteflies that over time translated into a population advantage for the newcomers, who probably originated in the Middle East and Mediterranean.
Immediately after the invasion, the two populations interbred because they could not tell each other apart. However, they cannot successfully reproduce.
This results in a greater number of male offspring because this species of aphid is a haplodiploid which means that males are produced from unfertilized eggs and females from fertilized eggs.
The invasive females respond to the ensuing abundance of males in their environment by becoming more promiscuous and having more frequent sex with those males they can mate with, which leads to an increase in female offspring.
In contrast, the indigenous females do not become more sexually active due to the increased availability of male partners.
What's more, the invading male aphids tend to court indigenous females as well as females from their own "clan," reducing opportunities for copulation between native aphids.
The upshot is that the proportion of females among the invading population of Biotype B insects keeps climbing, while the number of indigenous females goes down, eventually leading to extinction.
(Xinhua News Agency November 10, 2007)
