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The Best Defense

Researchers find tall goldenrod can "smell" its herbivore and initiate a defense.
Goldenrod / Gall Fly Life Cycle

Goldenrod / Gall Fly Life Cycle

It can't run from the fly that does it so much damage, but tall goldenrod can protect itself by first "smelling" its attacker and then initiating its defenses, according to researchers in the college.

"We found another weapon in the arsenal of defenses that plants might employ against 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," says Anjel Helms, postdoctoral fellow in entomology.

According to Helms, the gall-inducing flies (Eurosta solidaginis) are specialists that, in Pennsylvania, feed only on tall goldenrod (Solidago altissima). The male flies emit a blend of chemicals that is attractive to females. Once 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.

"The flies strongly reduce the plant's fitness by decreasing the number of seeds it produces, as well as the sizes of those seeds," says John Tooker, associate professor of entomology. "That's because when the plant's tissues are damaged by the insect, it diverts its energy away from seed production and instead toward production of the gall."

The team previously found that goldenrod plants exposed to chemicals from the male flies produced greater amounts of a defense chemical known as jasmonic acid when they were damaged by herbivores.

In their study, the scientists aimed to identify the specific chemical compound--E,S-conophthorin--goldenrod plants detect and determine how sensitive the plants are to the compounds.

"We found that goldenrod plants are sensitive to even small concentrations of this compound," says Tooker. "This is significant because it likely means that the plant has a dedicated mechanism to perceive this compound."

--Sara LaJeunesse