In the ongoing battle between plants and insects, Penn State researchers found a valuable weapon used by creatures.

Gary Felton, entomology department head, studied the effects of caterpillar saliva on plants.

Felton collaborated with research assistant Michelle Peiffer and various scientists from the University of Arkansas and Mississippi State University on the project.

He said this subject has been a popular topic among scientists. "In the last several years we've been questioning if the secretion of insects play a part in the outcome between the interactions with plants and insects," Felton said.

The saliva, which is produced by two pairs of saliva glands, is released through the spinnerets of the caterpillars, while they are feeding on plants.

To test the impact of saliva, Felton used caterpillars known to most people as corn earworms.

One group of caterpillars had their spinnerets cauterized, or closed shut, with heat. The other group was not altered in any way.

Both sets of caterpillars then were sent out to eat tobacco plants. The plants that were attacked by the cauterized caterpillars produced higher levels of nicotine.

The production of nicotine is the defensive response by plants to the actions of the caterpillars.

But the decreased amount of nicotine in the unaltered caterpillars show the insects can suppress the manufacturing of nicotine.

"People have the assumption that herbivores are passive, and are victims of what plants do to it," Felton said.

That is an important finding because scientists initially thought the saliva would alert the plant's defense, not play an active role in the insects' fight against the plants.

"I think it's amazing how the plants and insects have evolved with each other; constantly fighting with each other," Peiffer said.

The unaltered caterpillars, also, fared better health-wise due to the decreased nicotine content in the plants. Hydrogen peroxide was also detected where the insect was feeding. The peroxide tells the plant to increase its amount of nicotine, Felton said. "They use the production of peroxide as a signal," he said.

The researchers then wanted to find out what compound was in the caterpillar's saliva that affected the nicotine output.

Through a series of tests, Felton discovered that glucose oxidase was the active chemical in the saliva. Glucose oxidase is found in honey and it is used in beer and wine.

After finding and cloning the glucose oxidase gene, Felton injected it into the plant chromosomes. The plants subsequently became more resistant to bacteria and changes in temperature. "It's turning on a lot of responses in the plant that would affect its yield," Felton said.

The plant has to divert some of its resources toward defending itself, which lowers how much it can produce, he said.

Felton said the goal of the project was not to create a better tobacco plant, but to understand the dealings between plants and insects. "I am not going to release these plants," he said.

Felton's research has now moved on to tomato plants, which he said, is a close relative of tobacco plants. All of these findings from the research may bring better pest management techniques, Peiffer said.

"Only by understanding the interaction can we control the (insects) specifically, instead of broadly spraying pesticides," Peiffer said.