Locals lose out to sexy aliens

Invasive animals often thrive at the expense of their close indigenous relatives and a paper published today in Science within the Science Express web site provides some insights into why.

Scientists from China and Australia studied the silverleaf whitefly (SLW), Bemisia tabaci biotype B. In many regions of both countries native types of B. tabaci have been replaced by the invasive B biotype.

“This insect has spread from its Mediterranean-Asia Minor home range so successfully that it is now a global pest. It has even made it into the top 100 invasive species,” said Prof Liu Shu-Sheng from the Institute of Insect Sciences at Zhejiang University in China.

“We were trying to find out what made B. tabaci biotype B such a successful invader and the answer appears to be sex,” Dr Paul De Barro from CSIRO Entomology said.

“Whiteflies have an interesting sex life. Males are produced from unfertilised eggs and females from fertilised eggs.

“The different biotypes of B. tabaci look identical so when the B biotype invades, they can't tell each other apart. However, matings between the different types aren’t successful and this leads to an increase in the number of unfertilised eggs. So the first phase of invasion involves an increase in male offspring.”

In response to this increase in males, the invasive females become more promiscuous. And more frequent sex with the excess B biotype males leads to an increase in female offspring.

“To add insult to injury, the B biotype males are also more aggressive than the indigenous males. This means they displace the locals and cause mating interference between local males and females,” Dr De Barro said.

The end result of all this sex is a takeover of indigenous B. tabaci by the alien invaders.

In Australia, SLW damages crops by feeding and the growth of sooty mould on the sticky honeydew it secretes. It also spreads geminiviruses but this is not yet a significant issue here.