Ken Raffa, professor emeritus with the University of Wisconsin-Madison Department of Entomology. / Photo Credit: University of Wisconsin-Madison
By Art Kabelowsky, DNR Outreach and Communications, Fitchburg
Arthur.Kabelowsky@wisconsin.gov or 608-335-0167
Do you pity the poor tree, forced to stand defenseless against the ravages of insect pests, fungi and disease?
Then, you have not listened to Dr. Ken Raffa discuss the impressive natural defenses trees have developed.
Raffa, a professor emeritus with the University of Wisconsin-Madison’s Entomology Department, recently appeared on Proforest Podforest podcast to discuss the topic “Inside the Tree’s Natural Defense.”
He highlighted a host of tools that trees have developed to fight insect infestations and fungal diseases. “Tree defenses are multifaceted,” Raffa said. “They don’t rely on just one thing; they’re integrated.”
The logo of the Proforest Podforest podcast. / Graphic Credit: Proforest Podforest
Raffa said some of the defenses evolved by trees include:
- Tougher leaves and bark, “to keep insects from being able to attack their tissues.”
- Resins and gums that can “bind them up and entomb them,” much like amber.
- Trichomes, “which are tiny, sharp hairs that actually impale the insect, and they die a pretty ugly death on those things.”
- They develop silicon that “grinds the mandibles down while the insect is feeding on it,” leaving insects unable to feed.
- Simply dropping the leaves that are being attacked by insects or killing some of its own tissue when pests feed there. Raffa called that “the scorched-earth defense.”
- Chemical defenses that poison attacking insects, destroying their eggs and killing their larvae.
- Ecological alliances, such as trees that house ants that attack other predators and trees that produce chemicals that attract parasites to attack insects.
Raffa notes that trees “hold a lot in reserve” and turn on their defense mechanisms “once something starts to feed on them.”
He points out that while these naturally developed defenses work well against native enemies, trees are often left unprepared when invasive pests — such as spongy moth and emerald ash borer — enter the picture.
As Raffa puts it, “If you’re an insect trying to feed on plants, feeding on plants is a tough way to make a living.”