February 20, 2012 — Vol. 28 No. 7
Idaho State University's Leif Tapanila, an associate professor of geosciences, has found an important evolutionary event, documenting that insects bored into wood to use it as shelter from 200 to 210 million years ago during the Triassic period.
Tapanila, who is also a curator at the ISU Idaho Museum of Natural History, has examined petrified wood from Wolverine Petrified Forest, Grand Staircase-Escalante National Monument in southern Utah. He has documented that insects, likely beetles, were using wood for more than food more than 200 million years ago by boring into the wood and creating chambers for them to go through their pupa stage.
"This is the oldest occurrence of this we know of so far of using wood for more than just feeding," Tapanila said. "The insects were drilling into the wood and pupating, transforming through metamorphosis from caterpillar-like critters into adults."
Tapanila describes these findings in the paper "The Earliest Evidence of Holometabolan Insect Pupation in Conifer Wood" co-authored by Eric M. Roberts from James Cook University in Queensland, Australia, that was published in the journal PLoS ONE on Feb. 15.
Many insect species, such as beetles, go through this three-stage lifecycle, from larva to pupa to adult.
During the Triassic period beetles where just starting to "blossom" as a species and started to invade trees, Tapanila said.
"The insects and plants were evolving at the same time and here is an example of when insects were starting to develop these ties," he said. "This is a glimpse of a major (evolutionary) event that was happening."
Scientists have long had access to petrified wood samples that showed boring in the fossils caused by insects, but not much attention has been paid to it. Tapanila has determined that petrified wood samples show that insects bored into the wood and then back-filled with wood fiber, suggesting they used the wood for shelter.
"The insects were evolving using plant resources and the plants began responding," Tapanila said. "Our finding is significant as a milepost in establishing the close relationship between insect and plant evolution that really blossomed at this time, and is a dominant part of modern forest ecosystems."
It was earlier thought that social insects such as bees and termites were the first to colonize trees, but Tapanila said he believes the boring was done by beetles because of the size of the excavations in the wood, and the appearance that there was an entrance of a larva followed by the formation of the pupa and the adult emergence. Among the known fossil record of Triassic insects, Tapanila said cupedid beetles are the most likely creatures that made the borings, based on their body size and modern lifestyle.
The link to his story in the PLoS ONE journal is http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0031668.