Working beneath the towering oaks and maples on the U-M’s central campus Diag, undergraduate researchers and their faculty adviser helped explain an observation that had puzzled insect ecologists who study voracious leaf-munching gypsy moth caterpillars.

The caterpillars, which defoliate and sometimes kill stands of trees in the Upper Midwest and the Northeast, are especially fond of oaks, but sugar maple trees appear to be relatively resistant to the European pest.

Biologists wondered whether the caterpillars shun sugar maples in part because their leaves are less nutritious than the leaves of other trees. To find out, U-M biochemist Ray Barbehenn and several of his undergraduate research assistants compared the protein quality of red oak and sugar maple leaves from trees on the Diag.

What they found runs counter to conventional wisdom on the topic, which states that protein quality in leaves differs significantly from species to species. Instead, Barbehenn and his students found that the amino acid composition of the proteins in red oak and sugar maple leaves is strikingly similar – so similar, in fact, that they could not be distinguished during the spring, when gypsy moths do most of their feeding.

However, the researchers found that protein is more abundant in oak leaves than in maple leaves. Instead of differences in protein quality, we showed that maple trees have lower quantities of protein than oak, partly explaining why they are less nutritious than oak leaves," said Barbehenn, an associate research scientist in the Department of Ecology and Evolutionary Biology and the Department of Molecular, Cellular and Developmental Biology. The amount of essential amino acids in oak leaves was 30-42 percent higher than the EAA content of maple leaves in the spring and summer.

"These results help us understand the nutritional reasons why insects perform better or worse on different species of plants. This kind of information is needed in agriculture and forestry to improve the resistance of plants to insect pests," he said. "In the short term, though, this is basic research that is driven by the curiosity of ecologists to understand nature better."

The team's findings will be published in an upcoming edition of the journal Oecologia. Authors of the journal article are Barbehenn and two of his former undergraduate research assistants, Joseph Kochmanski and Julie Niewiadomski. Barbehenn has worked with more than 40 undergraduate research assistants since 2000.

Read the Oecologia paper

U-M News Service press release

On the U-M Gateway, click on the featured photos.

Captions: (top) U-M student research assistants Grace Lee (left) and Cara Mozola cut sugar maple leaves on the Diag as part of a study of leaf protein quality and gypsy moth caterpillars. Credit: U-M Undergraduate Research Opportunity Program.

A gypsy moth caterpillar. Credit: Richard Lindroth.