Figure: Goldenrod can detect a compound produced by gall-inducing flies, according to researchers. Image: Nick Sloff / Penn State

An international group of researchers has found another weapon in the arsenal of defenses that plants use to fight off their herbivore attackers, in this case eavesdropping on a very specific chemical signal from an herbivore to detect its presence and prepare for future attack," said Anjel Helms, postdoctoral fellow in entomology at the The Pennsylvania State University (Penn State).

The tall goldenrod plant protects itself from gall-inducing flies by "smelling" them first, and launching its defenses. According to Helms, the flies (Eurosta solidaginis) feed only on tall goldenrod (Solidago altissima). The male flies emit chemicals attractive to females. When the females arrive and the eggs are fertilized, the females deposit their eggs within the stem of a goldenrod plant. After the eggs hatch, the larvae begin feeding on the tissue inside the stem. Chemicals in the saliva of the larvae are thought to cause the plant to grow abnormally and form a gall, or protective casing of plant tissue, around the larvae.

In their study, the scientists identified the specific chemical compounds that goldenrod plants are detecting and determined how sensitive the plants are to the compounds. They found that the plants responded most strongly to the compound called E,S-conophthorin, the most abundant compound emitted by the flies. The researchers found that the goldenrod plants are sensitive to even small concentrations of the compound.

"The results provide evidence that goldenrod can detect a single compound from the fly, supporting the idea that there is a tight co-evolutionary relationship between these two species. Over time, as the fly has adapted to take advantage of the plant, the plant has adapted to protect itself from the fly," said John Tooker, associate professor of entomology at Penn State.

For more details, read the Penn State News.