BioEd Online

Researchers have discovered the gene that controls honeybees' sex. The finding could help us understand insect behaviour and evolution, and keep beehives healthy¹.

To become female, an insect needs two different versions of the gene, called csd. A male has one, occasionally two copies of the same version. There are at least a dozen different forms of csd.

Such a gene was mooted 50 years ago, and entomologist Robert Page of the University of California, Davis, has spent the past 15 years looking for it. "I expected it to take ten," he says.

Bee experts are delighted that Page's team has finally succeeded. "I'm super-excited about it - it really is a grail," says Jay Evans of the US Department of Agriculture's bee research laboratory in Beltsville, Maryland.

Males have no fathers

In bees, wasps and ants - the group of insects called the Hymenoptera - a fertilized egg develops into a female. Males are born of unfertilized eggs. The insects live in colonies comprising a few breeding females and a mass of female workers and a handful of male drones.

Much of these insects' intricate social life flows from the csd gene. Queen bees mate with many males - perhaps to ensure that they get a good mix of genes. And the fire ants currently invading the United States suffer from high levels of sterility, probably because they brought only a few versions of csd with them from their South American homeland.

Why such a sex-settling method evolved is a mystery, says Page. One possibility is that it favours females who are unable to find a mate: they can give birth to a son and then mate with him.

But inbreeding has a price. If a female mates with a male carrying her version of csd, half of her brood will develop into sterile males, despite being genetically female. Worker bees destroy these larvae. It's not clear why identical versions of csd cannot function together - "that's the next mystery", says Page.

For beekeepers, inbreeding bees is one way to select for docile insects that make copious honey and reproduce rapidly. But the heavy cost of sterility and fratricide had prevented this.

Pinpointing the gender gene will allow beekeepers to avoid this problem, says Evans, who is trying to breed disease-resistant bees. "Now we can scan the sperm of males and make sure we're crossing them with different mates," he says.

More important honeybee genes should be unveiled soon. The honeybee genome project, based at Baylor College of Medicine in Houston, Texas, completed its sequencing phase last month. Researchers are now assembling the genome.