One reason the trees thrive in Texas is that they're ignored by the local insect population. Siemann and Rogers have shown that Texas trees produce lower amounts of chemicals that deter insects, which allows them to grow faster than Asian varieties.

"It could be these chemicals are produced in lower quantities because they aren't needed, which allows the trees to put more energy into rapid growth," said Siemann. "It could also be that the genetic differences we've documented don't reflect changes that have taken place in North America but are due to the fact that trees came from different parts of China."

To study this, Siemann and Rogers this month received a $390,000 grant from the NSF to compare the genetic traits of tallow trees in China and the United States. The study will include trees from Texas, Hawaii and 10 provinces of China.

"One reason we're including Hawaii in our NSF research program is that tallow tree cultivation failed miserably there, largely because the Chinese rose beetle got to the islands long before the trees did," said Siemann. "During the '70s energy crisis, a privately funded group tried to grow Chinese tallow trees in Hawaii as a source of biomass for fuel, but the introduced Asian beetles just decimated the trees, especially those which were brought from Texas."

Reuniting Texas varieties of Chinese tallow tree and its native herbivores in China may help researchers understand its success in the U.S. If the combination of low defenses, fast growth and low insect attack is the secret to Chinese tallow tree's success in Texas, varieties collected in Texas and grown in China should exhibit lowered insect defenses and be easy prey for insects. But, when protected from insects, the invasive North American varietie
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Contact: Jade Boyd
jadeboyd@rice.edu
713-348-6778
Rice University
25-Aug-2003