英語時差：植物怎樣自我防衛(wèi)（下）

Even more sophisticated is the strategy used by a type of wild potato to defend itself against aphids. The plant manufactures the active ingredient of the so-called aphid alarm pheromone, a chemical that an aphid under attack releases into the air to warn other aphids of danger. Aphids run away from the wild potato plant’s chemical signal as if it were a danger signal from an aphid. There are a couple of general lessons to be drawn from the ecologists’ ever-growing collection of plant chemical-defense stories. One lesson is the importance of preserving the great natural diversity of plants, because we can learn so much chemistry from them. Also, the very specific nature of the chemical weapons used by many plants gives us hope that we humans can develop pesticides that will hurt only their intended targets.