Albuquerque, N.M., -- The forest tent caterpillar's eating habits may be the key to their ability to strip leaves without triggering the tree's defense mechanisms, according to a Penn State entomologist.
"Tent caterpillars are unique in their social lifestyle," says Dr. Jack Schultz, professor of entomology. "And this social eating pattern may be their protection against a tree's natural defenses."
All trees react when chewed on or leaves are broken. Oak leaves, for example, usually produce increased levels of tannins when ripped or chewed. Other caterpillars, like the gypsy moth, produce a response that is stronger than simply tearing the leaves.
"We allowed forest tent caterpillars to defoliate an oak tree and not only did the tree not respond by producing more tannins, there was a slight, but significant depression in the normal tannin production," Schultz told attendees at the Ecological Society of American Conference, today (Aug. 13) in Albuquerque. "The tent caterpillars seem to be chemically invisible to the tree."
Unlike the eastern tent caterpillar that builds large messy, very visible nests in cherry trees, the forest tent caterpillar builds only a small, resting place in an oak tree. Female moths lay eggs in one batch and the eggs hatch together. The forest tent caterpillars head for the crotch of a tree and spin a web as a place to rest while not eating.
Unlike most caterpillars, tent caterpillars eat together. They all march off to feed, focusing on defoliating one branch at a time. Together, they return to their nest, to rest. They continue this pattern all day long.
"Gypsy moths, which live in the same forests and attack the same trees as the forest tent caterpillar, eat leaves randomly," says Schultz, a faculty member in the College of Agricultural Sciences. "Both caterpillars can be equally destructive."
Schultz; Mark D'Ascenso, undergraduate student; and Dr. Heidi M. Appel, research associate in entomology, are interested in how trees react to tent caterpillars, and how tent and gypsy moth caterpillars influence each other. The tannins released by oak trees help the gypsy moths fight off a virus that normally kills them. Because caterpillar populations usually crash due to disease, researchers looking for ways to control these pests need to understand the complex interactions of the trees, caterpillars and microbes.
If forest tent caterpillars are eating their way from branch to branch on a tree, there is no response from the tree that will keep the virus from attacking gypsy moths.
"We do not understand how the tent caterpillar remains chemically invisible to the tree," says Schultz. "This stealth approach occurs because either the oaks cannot recognize and respond to forest tent caterpillar wounding, or the defoliation pattern caused by the semisocial forest tent caterpillar groups subverts induced responses."
The forest tent caterpillar may simply eat whole branches of leaves too rapidly for the tree to respond before all the leaves are gone. Or, the forest tent caterpillar may lack the chemical cue that turns the tree on in the case of the gypsy moth.
Growing trees resistant to insect pests is a long and difficult process. If the researchers could determine what makes the forest tent caterpillar a stealth caterpillar, then breeders might bioengineer into the tree the ability to not respond to the gypsy moth caterpillar. This would improve control of that pest.
"In Michigan, where the gypsy moth caterpillar is encountering aspen trees that do not produce tannins, the populations quickly succumb to disease and crash," says Schultz. "If we could prevent other trees from responding this way to gypsy moths, the same thing could happen."
EDITOR: Dr. Schultz may be reached at (814) 863-4438.
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