A、By flying in circles around a field B、By detecting a chemical signal C、By inspecting individual corn leaves D、By noticing the

Today, we are going to talk about a special way some plants respond to being invaded by pests. The plants react by emitting a chemical signal, which acts like a call for help. Let’s take corn plants for example. Sometimes, caterpillars chew on the corn leaves. When the caterpillar saliva mixes with the chew portion of a leave, the plant releases a chemical scream that attracts wasps. The wasps respond to the signal by flying to the chewed on leave, and laying their eggs on the caterpillars. The caterpillars die in the next few days as the wasp offspring nourish themselves by feeding of them. Thus the corn plant prevents all its leaves from being eaten by the caterpillars. This chemical scream is specific. It’s only released after the plant has detected the caterpillar saliva. A plant that is cut by in the other means does not give off the same signal, nor doesn’t undamaged plants. This also explains how a wasp can find a caterpillar in a huge field of corn. Soybean, cotton and probably many other plants use similar type of defense against pests. By enhancing this natural response in plants, researchers might reduce, some day even eliminate, the need for chemical pesticide, which can cause ecological damage. For example, scientists might breed plants for this screaming trait, or they might transplant specific genes to increase the release of the chemical signals.