Bacterial Nanny: Beewolf grows microbe for protecting young

For a new twist on child care, consider the wasp called the European beewolf. The mom leaves a smear of bacteria near each of her eggs as protection against the perils of youth.

This wasp carries an abundance of a particular bacterial species in glands in her antennae, reports Martin Kaltenpoth of the University of Würzburg in Germany. She applies a spot of white goo from these glands to a nursery chamber before she lays an egg. When the researchers covered the goo so that it didn’t contact the eggs and youngsters, most of the brood died from disease.

After a female European beewolf (Philanthus triangulum) catches a bee, she stings it into immobility and then lugs it back to a burrow she has dug in sandy ground. She tucks one to five honeybees into each of the chambers, where she later lays an egg. The bees, which remain alive, although paralyzed, for the first few days after a sting, serve as baby food.

Researchers have long known that female beewolf wasps secrete goo from their antennal glands. A decade ago, Erhard Strohm, one of the coauthors of the new paper, showed that the white spot orients young wasps in their chambers.

However, says Kaltenpoth, the earlier work had not figured out what was in the goo. While examining the wasp’s antennae with a scanning electron microscope, he and his colleagues got the idea for the new study. An image of an antenna’s gland showed branching, rodlike structures that looked like bacteria. With genetic techniques, the researchers identified a new species of Streptomyces.

The bacterium belongs to the same general microbial group as do species on the bodies of certain fungus-farming ants. The ants’ bacteria make an antibiotic that protects the insects’ fungus crop from disease (SN: 4/24/99, p. 261).

Kaltenpoth and his colleagues propose a similar defensive partnership between the newly discovered Streptomyces and the wasps. The young beewolves spend 4 to 9 months in a warm, humid cell where killer pathogens could thrive.

To test their idea, the researchers slid a thin glass rectangle over the white spot in some of the brood chambers. This prevented larvae from crawling around on the spot and perhaps even eating it. Of the 15 larvae deprived of the goo, only 1 lived to adulthood. Of 18 larvae permitted contact with the goo, 15 survived, the researchers report in the March 8 Current Biology.

Many other insects have been shown to host live-in bacteria, but these microbes supply nutrients or aid digestion.

The new wasp example is “the second clearly established defense relationship between insects and bacteria,” says Cameron Currie of the University of Wisconsin–Madison. He discovered the ant-bacteria relationship in 1999 and speculates that defensive relationships between insects and microbes might be common.