This summer's drought has caused plants literally to "cry" out for water as they wither, and scientists are trying to determine if their sounds - too highly pitched for the human ear - are attracting destructive insects.
Agriculture Department researchers have been using electronic gadgets for more than four years to hear corn and other drought-stressed plants make noises as cell structures, or water tubes, break down from a lack of water traveling from roots to the leaves.When there is adequate water in the soil, the water and nutrients flow upward in the tubes under tension. If the soil lacks enough water, the tension becomes too great and the tubes fracture.
One potential benefit from this kind of research would be new ways of letting irrigation farmers know precisely when to water their fields. Also it could aid in developing new plant varieties, which would be better equipped to move water and nutrients from roots to leaves.
Robert Haack, an entomologist at the department's North Central Forest Experiment Station, East Lansing, Mich., and a colleague, Bill Mattson, think there might be a connection between the noises and flocking of some insects, such as bark beetles, to drought-damaged trees.
The noises are called ultrasonic acoustic emissions, and are in the 100-kilohertz range, while sound heard by humans is no more than about 20 kilohertz.
While the ultrasonic emissions have been documented, their role in attracting insects remains only an educated guess.
Haack, the research leader, said in a telephone interview Wednesday from his East Lansing office, that he thought it was "a neat idea" that the noises of stricken trees might attract insects.
"We're just starting up" on the tree-insect project, he said. "We don't have enough to make any speculation on what we might find."
Haack said insects have been known for a long time to be attracted by certain influences such as color and scent. But Haack said that to the best of his knowledge there has not been conclusive work linking the ultrasound of trees to insect behavior.
The project only got under way three weeks ago, he said. A lot of time has been spent rounding up necessary equipment, part of it borrowed from other laboratories near Michigan State University, where the Forest Service operation is located.
"It could turn out that these sounds do attract insects," Haack said. In any case, Haack is starting by depriving potted white pine seedlings of water and recording their ultrasounds. The next step will be to see if the recorded sounds attract beetles.