Dances With Plants

Arthropods, especially insects, have had a long and close relationship with flowering plants that dates back between 135 and sixty-five million years ago. From the plant's point of view this relationship is both negative and positive. A negative example is their relationship with herbivorous insects. As herbivores, insects have strongly influenced the evolution of flowering plants. Over millions of years, plants have evolved several ways of defending themselves against insects. Many have developed bad-tasting chemicals, or toxins (TAK-sihns), that discourage herbivorous insects from eating their stems and leaves. Those plants that survived insect attacks were able to pass along their characteristics to the next generation through their seeds. At the same time, the defensive strategies of plants have influenced the evolution of insects. They have evolved systems within their bodies that breakdown these toxins into harmless chemicals so they can continue to eat the plant. Those insects that were able to get enough food were able to pass their characteristics on to the next generation through their eggs. Over time, plants and insects continued to change, or evolve, into new species as they attempt to overcome the attacks and defenses of the other. The mutual influence that plants and insects have over each other's evolution continues today and is called coevolution (ko-EH-vuh-LU-shun).

From a plant's point of view, pollination is an example of a positive interaction with insects. Plants produce flowers with nectar and more pollen than they need to reproduce to attract insects. Flowers are like brightly colored, sweet-smelling road signs that encourage insect pollinators to stop and visit. These pollinators either accidentally or purposefully collect pollen from the flower. Many flowers depend on bees, flies, beetles, and thrips to carry their pollen from one flower to another so their seeds will develop. Some species of orchids rely on specific insects to pollinate them. In fact, the flowers of some species mimic female wasps. Male wasps pollinate the flowers as they attempt to "mate" with the flower. This very special type of interaction between a plant and an insect is another example of coevolution.

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