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)
