Study predicts increase in insect herbivore damage with climate change

Ancient insects migrated northward and increased in diversity and abundance during a period when global temperatures gradually warmed about 60 million years ago, according to a study by Ellen Currano, assistant professor of geology at Miami University, and colleagues.

Their study - the cover article of the November issue of the journal Ecological Monographs - examined the long-term effects of temperature change on plants and insect herbivores in the fossil record of the Bighorn Basin, Wyoming.

“Based on our results, we predict that present-day anthropogenic warming will alter insect herbivore populations and distributions and cause a cumulative increase in herbivore damage at middle latitudes,” Currano said.

Plants and insects have coevolved for millions of years, and the long-term response of plants and insect herbivores to temperature change can be interpreted by analyzing insect herbivore damage on fossil plant leaves, the study authors reported.

They examined more than 9,000 fossilized leaves from nine sites in the Bighorn Basin that had fossils dating back 52.7 to 59 million years ago. This six million-year period includes both abrupt and gradual warming events, as well as an interval of cooling. Temperatures reached the greatest sustained highs of the last 65 million years during this period.

“The abrupt warming event 55.8 million years ago was caused by a sharp increase in greenhouse gases, and the speed and magnitude of climate change make it the best geologic analog for what is occurring today,” Currano explained.

They identified 107 plant species and recorded the presence or absence of 71 insect-feeding damage types. They found that the rise in global temperature led to an increase in insect populations and diversity. Surprisingly, the study authors said, they did not find a significant correlation between plant richness and insect herbivory, suggesting that climate change affects coevolutionary links between plants and insect herbivores.

“Our findings indicate possible changes to come as a result of anthropogenic climate change,” Currano said. “As temperatures rose some 60 million years ago, tropical and subtropical insects were able to migrate northward to Wyoming. It is likely that present-day anthropogenic warming will lead to similar distributions of insect populations and cause an increase in herbivore damage.”

The article, “Fossil insect folivory tracks paleotemperature for six million years,” written by Currano, Conrad Labandeira, department of paleobiology, Smithsonian Institution and department of entomology, University of Maryland, College Park; and Peter Wilf, department of geosciences, Pennsylvania State University, is available open access at online.

Currano joined Miami in the fall of 2009 after serving as a National Science Foundation Earth Sciences Postdoctoral Fellow at Southern Methodist University. She received her doctorate from the Pennsylvania State University in 2008. Her major research interests include the effects of climate change on plants and their insect herbivores, and the ecology and evolution of African plants and insect herbivores. Her research is supported by a recent grant from the National Geographic Society Committee for Research and Exploration.