It may sound like science fiction, but did you know some plants can call for help when they are being attacked by insects? Many people agree that plants do have feelings, simply because they react in certain ways when they are stimulated, but can they really call for help?

Research scientists at the USDA Agricultural Research Service in Gainesville, Florida, have found that when caterpillars chew on certain plants, chemical cues in their saliva cause the plants to send out defensive signals. Small wasps, which are natural enemies of the caterpillars, then follow the signals to find and sting the caterpillars. As they sting the caterpillars, the wasps deposit their eggs, which hatch into wasp larvas inside the caterpillars. These larvas then eat away the insides of the caterpillars as they mature. Even though they do not die quickly, once the caterpillars become infected, they become sick enough they stop chewing on the plant.

What is even more amazing is that the scientists have found that these plants can detect the differences in saliva from different kinds of caterpillars. They then send out the proper distress signal to attract that specific caterpillar's natural enemy.

We all get so involved in our own activities that we fail to realize the many interactions that are going on in nature all around us every day. In fact, even with the advancements recently made in plant and insect research, there is still much to be learned to help us understand how to manage or take advantage of these interactions.

As humans, we might ask, "so what?" What's the big deal that plants can call for help? By studying and better understanding these plant interactions, it may be possible one day to develop plant varieties with much more powerful chemical defenses against their own insect pests. If certain plants can develop greater chemical defenses against their natural pests, we may be able to grow these plants without the use of insecticides.

Those of us who love sweet corn are probably aware of the caterpillar that we often find in the end of the ear of corn as we shuck it. This caterpillar is appropriately called the corn earworm. It does considerable damage not only to corn but to many other crops as well.

The farmers who grow sweet corn know that we do not like to find corn earworms as we shuck back the ear. They know we like to shuck back a perfect, clean ear of corn every time. In order to provide us what we want, it is necessary for them to spray insecticides on the corn several times to kill the young caterpillars as they hatch and before they eat their way into the end of the ear of corn.

If corn plants can send out defensive signals to summon parasitic wasps every time a corn earworm starts gnawing away, the chemicals used to control these caterpillars would no longer be needed. I think all of us would be a lot more comfortable knowing the corn we were eating had not been sprayed several times with chemical caterpillar killers.

Another quick example of how insects respond to stimulation - USDA research scientists, working in conjunction with research scientists from Harpenden, England, have found that wheat aphids produce an alarm pheromone when they are threatened. Sensing this alarm, all wheat aphids in the area remove their feeding tubes (mouthparts) from the wheat leaves and try to move to secluded areas. In doing so, many of them fall from the plants and die before being able to climb back up the plants.

If scientists can determine how to make the plants secrete a substance that resembles this pheromone, or if they can develop something resembling this pheromone that can be sprayed across the wheat fields, aphids can be tricked into thinking they are being threatened and will cease feeding. Even if they did not die in the process, as long as they cease feeding on the plant, there would be little or no damage done to the plant.

I told you this stuff sounded like science fiction. You have to admit, it is fascinating what is going on in nature all around us every day.

E-mail address: Everett_Davis@ncsu.edu

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Date Created 09/13/01