2011年12月英语四级模拟试卷及答案分析(5)_第2页

　　Risky Business
　　Releasing one species of non-native bug to kill another could be risky business, potentially creating another type of infestation. But scientists first quarantined and studied the HWA-killer insects.
　　They believe the St beetles are the best answer to the HWA problem and that they won't cause side damage. This tiny black female beetle, the size of a poppy seed, is already spreading in the Great Smoky Mountains.
　　But the beetle and other HWA-killer insects are seasonal, so it will take several different ones operating year-round to keep HWA in check, Rhea said. He doesn't believe HWA will be completely eradicated (根除) but will instead be kept in balance by the predator insects. "We're trying to insert a balance in a system that's out of balance," he said.
　　Each St beetle can lay 200 to 300 eggs, said Ernest Bernard, professor of entomology at the University of Tennessee in Knoxville.
　　Bernard's laboratory is one of several that are breeding the beetles.
　　"Each beetle eats hundreds of baby adelgids a year," he said. And about 120,000 of the beetles have been released in the past couple years in the Smokies, but it is still too early to measure their impact.
　　One good sign, Bernard said, is that some beetle larvae (幼虫) have been found in areas where they were not released, indicating that the HWA killers may be reproducing and spreading.
　　1. The passage gives a general description of an invasive insect, HWA.
　　2. Hemlock is a hallmark of southern Appalachia's national parks.
　　3. The invasive insect, known as the hemlock woolly adelgid (HWA), is from Japan.
　　4. The key to killing the HWA is to catch it early and act quickly.
　　5. An infected tree usually dies immediately.
　　6. The Hemlock in the U.S. will be saved from HWA soon.
　　7. The long term, best way to control the pests HWA is spraying.
　　8. Since 1951 the HWA has spread to more than________.
　　9. Releasing one species of non-native bug to kill another could create________.
　　10. It will take several different insects operating year-round to________.