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This article is from the In-Depth Report The Buzz on Bees

Stingless Bees Mummify Enemies

Lacking a stinger is no barrier to kicking butt in the evolutionary cage match between Australian bees and hive-invading parasites
TRIGONA-ON-EUCALYPTUS



Mark K. Greco, Swiss Bee Research Centre

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Bees are under attack around the world. One of their nastiest foes: small hive beetles (Aethina tumida). Native to sub-Saharan Africa, these invaders can completely destroy the hives of common honeybees, which they have been pushing around throughout the U.S. and Australia.

"When [small hive beetles] invade a colony, their larval feeding and the spoilage that ensues converts the comb and honey into this lavalike substance. They make an incredible mess out of the comb and [bee] brood and everything else," says James Cane, an entomologist at the U.S. Department of Agriculture's (USDA) Pollinating Insect Biology, Management and Systematics Research Unit at Utah State University in Logan.

For a time, scientists were concerned that the parasite might also threaten Australia's native stingless bees (Trigona carbonaria), but it turns out these critters are made of tougher stuff than their European honeybee cousins.

Researchers recently discovered that although they lack stingers, these bees are pros at immobilizing interlopers. Mark Greco and Peter Neumann, entomologists at the Swiss Bee Research Center in Bern, discovered that as soon as the beetles enter a hive, worker bees in the colony surround them and force them to immediately pull their legs under their carapaces, adopting what is known as the "turtle" protective posture. This stance employs the beetles' hard shells to shield them from attack, but it also prevents them from moving. Worker bees take advantage of this, gluing the immobile beetles to the walls of the hive with resin collected from plants; they then "mummify" their captives with a substance called batumen, a mix of plant resins, wax and mud.

View photos of Mummifying Bees

Greco says he and Neumann call the process mummification because "the beetles remain incapable of moving, and therefore die."

Honeybees exhibit a similar behavior, called social isolation, but it is significantly less effective against the small hive beetle. To isolate the invaders, honeybees construct small chambers around the beetles, but do not seal them off completely. Instead worker bees guard the entrances of these chambers, which often allows the beetles enough time to mate and produce their hive-trashing larvae. In contrast, the stingless bees' mummification process takes a total of 10 minutes from start to finish, at which point the beetle is completely immobilized and starves to death without any further attention from the members of the hive.

The researchers discovered this rapid mummification behavior by taking high-resolution digital x-rays of entire hives with medical computed tomography (CT) scanners, a new twist on an old procedure known as radioentomology.

"It is really kind of a novel approach," says Jeff Pettis, research leader at the USDA's Bee Research Laboratory in Beltsville, Md. "You can get at some biological questions that you can't get at otherwise."

Greco and Neumann report in Nature Precedings that they were able to witness the entire battle between the bees and beetles play out in high-resolution 3-D by using a "micro CT" scanner that took snapshots of a stingless bee hive every five minutes for an hour and a half.

Even though the study was published on a prepress service, which means it has yet to be peer-reviewed, other experts in the field praised the authors' methodology and findings.

"It's a really clever way to keep track of what's in the colony without having to take apart the colony," says Christina Grozinger, an associate professor of entomology at Pennsylvania Sate University in University Park.

Ultimately, this research may help Australian growers reduce their dependence on the relatively vulnerable European honeybee. It turns out that stingless bees are better than honeybees at pollinating peppers, a commercially important crop in Australia.

"We place manufactured beehives containing colonies of these bees in the greenhouses," Greco says, "and the bees pollinate the vegetables without stinging the workers."

 
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