NewScientist.com news service
John Pickrell
The queens of bees, ants and wasps that indulge in the most promiscuous and lengthy sex marathons produce the healthiest colonies, a new study reveals.
Honeybee queens that mated with multiple drones were shown to foster bee hives with wider genetic variation. This variation meant they were much better able to fend off a debilitating disease, researchers found.
For many social insect queens, mating is a costly activity. In honeybees, for example, it involves her flying many kilometres from the hive to rendezvous sites with male drones – the longer she stays to mate, the more precious energy she expends, and the greater the chance there is that she will be devoured by predators.
This has made experts wonder why the queens of some species of social insects indulge in multiple sexual encounters, while others make do with a single male. Ideas include that the resulting genetic variation could help improve the division of labour in a colony, or that multiple mating might simply be a strategy to collect more sperm.
(In the picture:Queen bees, such as the one marked with a numbered tag, foster healthier colonies by 'sleeping around' (Image: David Tarpy))
Hotbed for life
But perhaps the most convincing theory is that queens that take many lovers produce colonies that are better protected against disease. "Insects living very closely in nutrient-rich environments are hotbeds for micro-organisms – they need mechanisms to protect against disease," says apiculturalist (bee expert) David Tarpy at North Carolina State University in Raleigh, US.
To test this theory, Tarpy experimentally inseminated honeybee queens (Apis mellifera) with the sperm of either one or 10 drones. Twenty-four "multiple-mate" queens and 25 singly-mated queens were then encouraged to set up colonies in bee hives kept by Tarpy's colleague Thomas Seeley at Cornell University in Ithaca, US.
Once these colonies were established, Seeley sprayed them with water tainted with American foulbrood disease, a highly virulent infector of bee larvae.
The hives were tested for spread of infection five and nine weeks later. Though no colonies had completely escaped infection, the researchers found that colonies fathered by single drones were significantly weaker and were experiencing more intense outbreaks of disease.
Wipe out
The findings strongly suggest that multiple mating increases a colony's resistance to parasites, Tarpy says. "Honeybee queens are hedging their bets by mating with many males," he says. The resultant offspring would have a wider range of disease resistance and susceptibilities, meaning they are less likely to be wiped out in one go.
"This is convincing evidence that multiple-mated hives seem to suffer less disease," says Francis Ratnieks, who heads up Sheffield University's Apiculture and Social Insect Laboratory in the UK. "There are lots of ideas in this area, but not many good experimental studies."
The finding could have wider implications. Honeybees are thought to be directly responsible for about one-third of everything eaten in the US, due to service they provide as pollinators, says Tarpy. They are therefore worth an estimated $20 billion annually to the agricultural industry. Many of these are domesticated bees, and some are artificially inseminated.
Though honeybees naturally take 10 to 20 mates – beekeepers could help ensure hives are steeled against the ravages of disease by ensuring queens are as promiscuous as possible, perhaps through artificial insemination, says Tarpy.
Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2006.3702)
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