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Bully bees eat others out of hive and home

A.m.capensis & A.m. scutellata

Get out of my house: The yellow bee is Apis mellifera scutellata, the species to whom the hive belongs. The black bee is Apis mellifera capensis. (Pic: Per Kryger)

An unprecedented movement of bees in South Africa has revealed the nasty habit of a particular honeybee — it likes to take over the honeybee colonies of other subspecies and wipe them out.

The Apis mellifera capensis worker bees have been called 'parasitic' by the researchers studying their behaviour. They have the ability to lay eggs with a full complement of chromosomes, effectively 'cloning' themselves.

The research appeared as a letter in this week's Nature.

In normal bee colonies, the queen does all the reproducing. Nearly all workers are undeveloped females: only a few have fully active ovaries able to produce eggs, and even those eggs are then killed by other workers without being fertilised.

The drones are males which hatch, mate with the queen and die. The queen stores this sperm and uses it to fertilise eggs as required.

"But the A. m. capensis — Cape honeybees — are an exception," explained team member Dr Madeleine Beekman, postdoctoral fellow in Applied Mathematics at the University of Sydney.

"Even though the workers don't mate, they can produce diploid offspring that produce new workers."

Diploid eggs have the full complement of chromosomes, which means the offspring have exactly the same genes as the parent. In normal reproduction, an egg has half the number of chromosomes with the other half being provided by the male.

Queens emit pheromones when they produce eggs, which is a signal to the other workers not to develop their ovaries. But when Cape honeybees are in the hive of another subspecies, A. m. scutellata, they can activate their ovaries even in the presence of a queen.

It is probable that all subspecies of Apis mellifera have the capability of producing dipolid offspring. "But whether they do, we don't know," explained Dr Beekman.

"It is likely some are just quicker than others. Once they start producing eggs, they also start to elicit pheromones like honeybee queens do."

The problem is these diploid offspring don't forage for food. The A. m. scutellata bees forage and bring food to the diploid-producing bees because they smell like the queen.

As the Cape honeybees produce more offspring, the ratio of foragers to non-foragers becomes overbalanced, so eventually the colony dies.

"They actually kill themselves," said Dr Beekman. "So what they have to do is make sure that before the colony dies they spread themselves and disperse and find other host colonies."

"They are really a disease."

Normally the two sub-species do not live in close proximity. This phenomenon has only been noticed in the past decade after bee-keepers in South Africa moved Cape honeybees from the South to the North, bringing them in close contact with the managed, honey-producing A.m. scutellata.

"It is a big disaster because the bee keepers depend on the African honeybee colonies, and they go broke," explained Dr Beekman.

"It really is a big problem."