Have you ever started talking to someone, only to discover you have nothing in common and, therefore, nothing to say? You might imagine that a yellow jacket, flying about its waspy business, and a rose bush, intent on growing green leaves in the sun, would be in a similar fix: nothing in common, nothing to say. Actually, rose bushes and other plants have a time honored method of communicating with yellow jackets and other wasps.
A yellow jacket's waspy business is probably finding food. One of the things it likes to eat is nice, juicy caterpillars. The caterpillar, of course, likes to eat nice, green leaves. So you see, the plant and the yellow jacket have something in common after all: The plant is eaten by the very thing the wasp likes to eat.
Yellow jackets have good eyes for spotting caterpillars and other prey, but a plant that is being eaten doesn't want to just wait around for the wasp to notice. Fortunately for your roses, evolution has provided the plant with its very own distress signal, based on smell. When a caterpillar chomps into a leaf, the plant releases an acid that smells the same as fresh cut grass. The caterpillar's bites also spill a kind of alcohol from the damaged leaf cells. This alcohol mixes with the cut grass aroma and carries it upward in a rising plume where it can be smelled by our circling yellow jacket. Millions of years of evolution have taught the yellow jacket that following this smell often leads to a delicious meal.
So what do wasps and roses talk about? They talk about what's for lunch.