The Beeholder, January 2009.

Bees can be good for plants in more ways than one. Researchers in Germany discovered that the flapping of bees' wings scared off caterpillars, reducing leaf damage. Many wasp species lay their eggs in caterpillars, and so caterpillars have evolved mechanisms to avoid them. The sounds of bees' and wasps' wings are similar.

Writing in the journal Current Biology, the scientists suggest this is an added bonus of having bees around, as well as the pollination they provide.

"Our findings indicate for the first time that visiting honeybees provide plants with a totally unexpected advantage," they write. "They not only transport pollen from flower to flower, but in addition also reduce plant destruction by herbivores."

The experiment used bell pepper and soybean plants, beet-armyworm caterpillars, and honeybees. Researchers set up experimental plots of the plants, added the caterpillars, and allowed the bees to enter some of the plots but not others. When the caterpillars had turned into pupae and buried away in the soil, the scientists went back into the cages and measured the extent of leaf damage - the amount of munching that the caterpillars had indulged in.

In plants that had not fruited, the presence of bees reduced caterpillar damage by about 60%. The researchers believe the caterpillars were sensing the bees' presence through the tiny hairs on their bodies, which enable them to detect vibrations in the air.

"These sensory hairs are not fine-tuned," said lead researcher Jurgen Tautz from the Biozentrum at Wurzburg University. "Therefore, caterpillars cannot distinguish between hunting wasps and harmless bees."

When plants had borne fruit, the caterpillars were able to hide in the fruit and the bees had much less effect.

from an article by Richard Black BBC’s Environment correspondent 22nd Dec 2008