Over time, goldenrod plants and the gall flies that feed on them have been one-upping each other in an ongoing competition for survival. Now, a team of researchers has discovered that by detecting the plants' chemical defenses, the insects may have taken the lead. According to John Tooker, PhD, Professor of Entomology in the Department of Entomology at Penn State, this complex scenario begins when a female gall fly (Eurosta solidaginis) lays its eggs in the leaf bud of a goldenrod plant (Solidago altissima). This action forces the plant to produce a tumor-like growth, called a gall. This gall, he said, provides the fly larvae with a source of nutrition and safety from predators and the environment, but decreases the plants' ability to reproduce. "Our previous research showed that goldenrod plants have evolved to 'eavesdrop' on the sexual communications of their gall fly herbivores -- specifically, the sex pheromones used by males to attract females," he said. "Our new research, suggests that the plants respond to this 'intelligence' by strengthening, also known as 'priming,' chemical defenses to prevent females from laying eggs and inducing gall formation." Eric Yip, PhD, postdoctoral scholar in the Department of Entomology, Penn State, explained that this plant-insect dynamic is similar to the reversals of fortune that occur in the "Spy vs. Spy" comic strip, only the characters are a plant and an insect rather than a pair of cartoon drawings. To investigate the effects of priming, the researchers, in their new study, exposed almost 300 goldenrod plants comprising 11 genetic types--or genotypes--to male gall flies that varied in age, from one to four weeks old, as well as a control in which the plants were not exposed to flies.
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