Wasps' Nursery Defense

Cultivating bacteria in one's antennae might seem like an eccentric pastime for female beewolf digger wasps, Philanthus triangulum, but new research reveals that the insects grow the microbial crop to protect their offspring from infectious pathogens.

Just before laying eggs, a female beewolf wasp uses Streptomyces cultures in her antennae as a paint to coat the walls of the underground nursery where she lays her eggs. The Streptomyces bacteria produce a cocktail of nine antibiotics that protect the larvae that eventually hatch from those eggs "in a manner similar to combination therapy used in human medicine," says Aleš Svatoš at Max Planck Institute for Chemical Ecology, in Jena, Germany, who led the research with Johannes Kroiss and Martin Kaltenpoth (Nat. Chem. Biol., DOI: 10.10381nchembio.331).

The antibiotics produced by the symbiotic bacteria, which include streptochlorin and eight piericidin derivatives, "may be only somewhat active alone but when in combination are fantastically potent" against pathogenic bacteria and fungi that live in the same soil in which the wasps dig their underground nurseries, comments John A. Pickett, a biological chemist at Rothamsted Research, an agricultural research center in Harpenden, England.

In addition to providing a chemical explanation for the symbiotic relationship between the wasps and the bacteria, the study involved a "brilliant" analytical setup that could be useful for other chemical ecology research, Pickett adds. In particular, the team made in situ measurements using imaging mass spectrometry to monitor levels of the antibiotics produced by the bacteria that colonize the cocoon that surrounds each developing larva in the nursery.

Researchers would have normally taken a sample of the symbiotic bacteria, grown it in a lab, and examined what antibiotics the bacteria produced or done a genome analysis to see what chemicals the bacteria were capable of producing, comments Jon Clardy, a natural products chemist at Harvard Medical School. In the new work, the researchers were able to analyze "ecologically relevant samples," he says.

Next up is figuring out what precisely the bacteria get from their relationship with the wasp, Kaltenpoth says. Bacteria likely receive some nutrient in the wasp's antenna glands, he says, because the bacteria grow rapidly once they have colonized the antenna gland right after the wasp breaks through the cocoon. The research team is also planning to evaluate whether this symbiotic method of protecting nurseries is used by other wasp species, too.