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Prehistoric beetles bored trees for more than food

Published February 27, 2012 11:32 pm

Science • Former Utahn's research shows evolution of relationship between plants and insects.
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Beetles who bore into trees are anything but boring to former Utah paleontologist Leif Tapanila, whose research shows the insect may have been burrowing into trees far longer — and for different reasons — than scientists believed.

The Idaho State University associate professor of geoscience and curator of its natural history museum recently published a paper on research he conducted with a colleague on petrified wood from southern Utah's Grand Staircase-Escalante National Monument. What they found indicates beetles were boring into wood as part of their life cycle, not just for food.

"Our finding is significant as a milepost in establishing the close relationship between insect and plant evolution that really blossomed at this time [Triassic period]," said Tapanila, who earned his doctorate at the University of Utah.

Tapanila and Eric Roberts, a professor of geology at James Cook University in Queensland, Australia, published their findings in the Feb. 15 edition of the online journal PLoS ONE. They believe that during the Triassic period about 210 million years ago, beetle larva were boring into trees where they would develop during the pupa stage before emerging as adults. Excrement they left behind them plugged the holes.

Until now, scientists believed the beetles had used trees just as a food source.

"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 said that while insect body fossils are rare, trace evidence resulting from their behavior is preserved in the geologic record and can be used to form hypotheses. In this case, the trace evidence is excrement that the insects left behind in the trees. He said he found similar evidence in petrified wood from Arizona, creating a bit of a buzz among paleontologists.

Tapanilla's and Roberts' research challenges the earlier assumptions published in the 1990s that the bores were the work of an early relative of today's bee. Tapanila believes the boring was done by beetles because of the size of the excavations in the wood, and evidence that a larva burrowed but an adult emerged by a different path. He said evidence of bees doesn't appear until later in history.

But University of Kansas geologist Stephen Hasiotis, who published the research on wood samples from the Petrified Forest National Park in Arizona, said his findings led him to theorize that bees were boring into the ancient trees and depositing eggs that hatched into larvae that fed on nutrients like pollen or spores before emerging as adults.

He said bores he studied do not indicate they were sealed with excrement, but rather with a cap on the exterior of the tree created by an adult bee. Offspring, he said, emerged through the original bore path.

According to Hasiotis, the earliest evidence of bees dates to about 100 million years ago, but that doesn't mean bees did not exist earlier. "There can be huge gaps in the geologic record."

Hasiotis said there is no conclusive proof that beetles and bees didn't exist at the same time.

Michael Getty, paleontology collections manager at the Natural History Museum of Utah, said the specimens used in Tapanila's study will join a growing list of fossil discoveries from the near 100-million-acre monument created in 1996, which is proving to be a paleontological treasure trove.

He said the museum's collection from the monument spans the Mesozoic Era from more than 200 million years ago to the end of the Jurassic period 60 million years ago, and includes the age of dinosaurs.

The collection contains an extensive fossil record of plants from the Triassic and that the new evidence suggesting early interaction between plants and insects is significant.

Tapanila remarked on the plethora of fossils on the monument in portions of Kane and Garfield counties, saying it was hard to stay focused on fossilized plants while exploring the area.

"There were bones sticking out of the ground everywhere that caught my eye," he said.

mhavnes@sltrib.com