I Talk to the Trees

I talk to the trees. But they never listen to me. I used to think they were just ignoring me. But now I find out they are too busy talking to themselves. What, you might ask, would trees have to say to each other?

If an animal is attacked, it usually has the option to flee rather than stick around and be eaten. Trees and other plants – solidly rooted in the ground- don’t have that option. To us, they might seem like easy targets for their predators – mostly insects that feed on their leaves. What is to prevent a bunch of caterpillars from eating to their hearts content till there are no more leaves on the tree? Think back to the last big outbreak of the Gypsy Moth. It seems that the trees didn’t stand a chance. Did you ever wonder how the trees survived this onslaught? Probably by good communication.

Trees, and plants in general, are not as defenseless as they seem. Their defenses consist mostly of poisonous chemicals. One such chemical that you might be familiar with is tannin. These tannins are common in oak trees. Bite into an oak leaf and notice how bitter it is. Another noxious plant chemical you might be familiar with is nicotine.

Producing these defensive chemicals requires a certain amount of energy put out by the plant, energy that might be needed to produce seed - the primary goal of plants. So here is the quandary plants face - save your energy for seed and hope you don't get attacked by caterpillars or protect yourself from caterpillars and hope you have enough energy left for seed production. Some recent research gives a little insight how plants might circumvent this problem.

Studies on a wild tobacco plant show low levels of nicotine in the plant's leaves. When caterpillars start to munch on the leaves, the plants begin to increase their production of nicotine. This decreases their palatability to the caterpillars. It is amazing to think that plants - with no brain whatsoever, can react to a stimulus like being chewed on.

The increase of nicotine in the plant's leaves did have an effect on the feeding of most caterpillars. But not all caterpillars are affected by nicotine. The scientists discovered that when these caterpillars fed on the plant, there was no increase in nicotine, instead the plant produced another noxious chemical. The plants were not only able to react to being fed on, they could suit their response to the individual caterpillar! Scientists are not sure how the plants could tell who was feeding on them, but they have as good idea.

When the scientists injured the leaves, trying to imitate the damage done by the caterpillars, the plants did not respond. However, when they added some of the oral secretions of the caterpillar to the wound, the plants began to produce the proper chemicals. The saliva of the caterpillars was the clue as to who was feeding and what protection was needed!

This is all well and good. But once the caterpillars get established on the plant, they are hard to control, even with the proper chemical defenses. It would be much better to start to build up your defenses just before the insects arrive.

Scientists observed that when certain leaf-eating beetles feed on a plant, the plants downwind started to produce the chemicals before they were even attacked. These downwind plants were "listening in" to their brethren that were being eaten.This gave them enough time to start raising their defenses as the enemy approached!

Sometimes, despite the plant’s best efforts, the predators are just too overwhelming. It sure would be nice to have an ally help you out. Well, it seems that many plants do have allies. Some of the chemicals that the plants release, along with the oral secretions of the insect pests, attract parasitic wasps - wasps that lay their eggs in the insect’s body, eventually killing it. These chemicals help the wasps locate their prey. It doesn’t matter how well the insect is camouflaged or hidden, the wasp just follows it’s nose (so to speak). Sometimes, up to 80% of the insect pests on a plant can be eliminated in this way.

So it seems plants have a lot to say, like, "Look out, here comes trouble", or, "I need some help over here". Unfortunately, they speak in a language I don’t understand. Too bad. Seems like there are a lot of interesting conversations going on in the woods.

If you are interested in nature you can find in your backyard check out the author’s website at: http://www.backyardbiology.net