英語時(shí)差：植物怎樣自我防衛(wèi)（上）

Most animals prefer to eat them. They can’t hit back or run away. Yet plants dominate vast areas of Earth’s continents. How Can Plants Have So Many Natural Enemies And Yet Be So Successful? Of course, some plants have physical defenses such as thorns and spines. But ecologists are finding that many more plants use chemical weapons to defend themselves. Some plants make their own insect repellents and insect poisons — a simple but effective strategy. Other plants make chemicals that closely resemble insect hormones. An insect larva feeding on such a plant may have its development disrupted. For example, an African plant called the bugleweed has been found to make an imitation insect hormone that causes many insect larvae to grow two or three heads. The mouthparts of a multi-headed larva don’t work properly, so the larva starves to death.