A new study reveals that the healthiest colonies of Hymenoptera ("thin wings") insects (bees, ants, wasps) are produced by females (" queens") which indulge in the most promiscuous sexual encounters.

Honeybee queens mating with multiple drones produced colonies possessing a wider genetic variation.

This variation would result in an increase of their resistance to diseases.

Queens' mating is a costly activity, so there must be a precise goal for this activity.

The honeybees' queen must fly many kilometers to mating sites with male drones and the longer she spends to mate, her energy burnings increase and so happens with the peril of being consumed by predators.

So why the queens of some species of social insects indulge in multiple sexual encounters, while others are monogamous (mate with only one male)?

Amongst many theories, some assume that the resulting genetic variation could help improve the division of labor in a colony, or that multiple mating might simply be a strategy to collect more sperm.

The most convincing theory is that queens that polyandrous (mate with more than one male) 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 bee expert David Tarpy at North Carolina State University in Raleigh, US.

His team inseminated honeybee queens with the sperm of either one or 10 drones.

The queens were then encouraged to set up colonies.

These colonies were infected with American foulbrood disease, a highly virulent germ of bee larvae.

Five and nine weeks later, the hives were tested for spread of infection.

The team found that colonies fathered by single drones were significantly weaker and were experiencing more intense outbreaks of disease, even if no colonies had completely escaped infection.

"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".

The results could have an economic impact.

"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.