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Plant Defence 101: Sensing Insects

Do plants have senses? Can they feel when they are being damaged? They most certainly can! And it gets even better…

First, I would like you to think about that first question for a moment. Do plants have senses?

You might find it quite difficult to come to an answer, right? That is probably because it is hard to define what senses really are. If it has to include seeing, hearing, smelling and so on, then no, plants do not have senses. But if sensing is more something like the ability to collect information from the environment and react to that, then plants most certainly qualify.

In animals, sensing happens through pathways consisting of nerves, hormones, or both. The information either goes to our brain, or triggers an immediate reflex. It is a quite complex system, leaving many variables to depend on all kinds of individual situations.
Plants do that a bit differently. They only use hormones to transmit information. And of course, they lack a central organ like our brains. Which might lead you to say that the system in plants is thus less complicated. But the thing is, without nerves and a brain, it is actually quite ingenious how plants manage to react to things they feel and have very distinct parts of their “body”, each with its own task.

Although plants do not have our set of senses, they can feel different environmental conditions. Some of those trigger an immediate response through short, direct effects, like closing off their pores to prevent water loss, but others take a longer pathway.
One case where such a long pathway is used, is when insects are involved. Insects often feed on plants, so it is almost imperative for plants to be able to react to them. And in order to do that, they have to sense the insects first.

can plants sense insects

So, say for example that a caterpillar finds its way to a plant and starts munching on its leaves. The damaged plant cells then immediately send out a warning. They do so by producing hormones that are transported through the plants’ vein system. The hormones can trigger different defence responses, depending on the plant, and sometimes even on the type of insect. On of the most common reactions would be to transport (or produce) a toxic compound to the damaged leave. The caterpillar will be feeling sick, having pain or even die and over time they might learn to leave that plant alone. Or at least they will stop eating pretty quickly.

But it doesn’t stop there! Some plants can even sense when a butterfly deposits her eggs on one of its leaves. Even with the eggs only glued to the outside of the leaves, the plant will respond to the invasion. After all, as soon as those eggs hatch, the baby caterpillars will start eating the plant. Better to prevent them from hatching at all, right?
To get rid of the eggs, plants sometimes decide to regulate the death of all the cells underneath and around that particular spot. If the eggs have nothing to attach to, they will fall to the ground. Of course this tactic also has its cost on the plant, as it loses perfectly healthy cells. But in many cases, the loss of those cells is much smaller than that of the damage the caterpillers will do otherwise.

There also is another option the plant can choose, either when being under direct attack or when infested with eggs. In that case the plant will get help from outside. It will call in reinforcements in its battle against insects. And those reinforcements are… other insects! But the next Plant Defence 101 will explain that process in more detail.

Would you have thought plants could sense things like this? It’s amazing how they are much more aware of their environment than you might have thought, isn’t it?

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  • Reply Bernette

    What a fascinating article! Love it!

    11/06/16 at 14:09
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