COURTESY OF PLOS BIOLOGY AND JUNJI TAKABAYASHI

Rise and shine.
Chemicals released by corn plants let caterpillars know when it's time to wake up.

Wake Up and Smell the Corn

It may not taste like Starbuck's coffee, but caterpillars apparently have their own version of brew to get them going: plant chemicals. A new study has found that nocturnal caterpillars called Mythimna separate spring to life each evening when they get a whiff of certain plant scents.

Most organisms can tell the difference between night and day simply by taking a look outside. But some may rely on more subtle clues. A few years ago, scientists discovered that corn plants release a different set of chemicals into the air in the morning and evening. Might the M. separate caterpillars, which live on corn plants throughout Asia, use these odors to plan their schedules?

A group of researchers at Kyoto University in Japan decided to test the theory by collecting gas from the plants during the day and at night. They then exposed one set of caterpillar larvae to the daytime fumes and another set to the evening fumes and observed the larvae for several hours. The creatures were almost 50% more likely to go into hiding--which they typically do during the daytime--after being exposed to the "day" fumes than they were when exposed to the "night" fumes. Night fumes made the caterpillars come out of hiding to feed on leaves, their typical evening activity. Surprisingly, changing the lighting conditions had no effect on the caterpillar behavior, indicating that the insects use plant scent alone as an alarm clock, says study co-author Junji Takabayashi.

The caterpillars are believed to have evolved a nocturnal lifestyle in order to avoid predatory wasps that maraud throughout the day, but why they don't use light cues like most other organisms remains a mystery, Takabayashi says. The team, which published its findings online today in PLoS Biology, is now trying to identify the exact chemical compound that the caterpillars respond to.

Scientists are increasingly recognizing the importance of plant chemicals in regulating insect behaviors such as foraging and mating, says James Tumlinson, a plant chemist at Pennsylvania State University in State College. And these findings may have a practical application. Exposing pest caterpillars to certain plant scents may put them to sleep or make them more susceptible to pesticides, says David James, an entomologist at Washington State University in Prosser.

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