Summer 2011

On Henry Mall

Calling the shots: A queen paper wasp (Polistes fuscatus) on her nest. Eggs and water droplets are visible in the next cells. Photo courtesy Sainath Suryanarayanan

Future queen or tireless toiler? A paper wasp’s destiny may be set by the rhythmic vibrations of its colony caretakers.

Like many social insects, paper wasps have distinct castes. Workers build the nest and care for the young, while “gynes,” which hatch late in the season, can become queens. Both hatch from eggs laid by the colony’s queen and tend to look alike, but the similarities end there. Gynes, unlike workers, develop large stores of body fat and other nutrients to help them survive the winter, start a new nest and produce eggs.

“The puzzle has been how the same egg and the same genome can give rise to two such divergent phenotypes,” says Sainath Suryanarayanan, a researcher in the department of community and environmental sociology.

The answer might lie in the music. While feeding a colony’s larvae, the paper wasp queen and other dominant females periodically beat their antennae in a rhythmic pattern against the nest chambers. This antennal drumming is in some instances clearly audible even to humans and was thought to be a type of communication, says Robert Jeanne, a CALS professor emeritus of entomology. But its purpose was unknown.

Now Suryanarayanan and Jeanne have shown that antennal drumming may drive developing larvae toward a lifetime of labor.

In the lab, they simulated the vibrations of antennal drumming using piezoelectric devices designed by John Hermanson, an engineer at the USDA Forest Products Laboratory in Madison. Vibrating the late-season nests—which normally would hatch gynes—instead produced wasps resembling workers, with much lower fat stores.

“We think it initiates a biochemical signaling cascade of events,” says Suryanarayanan. “Larvae who receive this drumming may express a set of genes that is different from larvae who don’t—genes for proteins that relate to caste.” These could be hormones, neurotransmitters or other small biologically active molecules.

The researchers’ conclusions mesh well with field observations that antennal drumming is common early in the season when colonies are pumping out workers but drops to nearly zero by late summer, when the reproductive wasps—males and future queens—are being reared.

Studies in other species also have shown that vibrations can have profound effects on animal development and physiology, Jeanne notes. In one study, young mice exposed to low-frequency vibrations developed less fat and more bone mass than other mice.

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