首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
To Save Trees, Fighting One Alien Insect with Others Rusty Rhea sighs wistfully as he talks about the beauty and peace of st
To Save Trees, Fighting One Alien Insect with Others Rusty Rhea sighs wistfully as he talks about the beauty and peace of st
admin
2012-10-30
37
问题
To Save Trees, Fighting One Alien Insect with Others
Rusty Rhea sighs wistfully as he talks about the beauty and peace of standing amid a grove (小树林) of deep green hemlocks in Appalachia, some of them up to 160 feet (50 meters) tall and more than 500 years old.
"This is a very special tree," said Rhea, an entomologist for the U.S. Forest Service’s Forest Health Protection program in Asheville, North Carolina. "I was brought up here, and I don’t want to see another species go by the wayside."
The evergreen trees, a hallmark of southern Appalachia’s national parks, are under attack by an invasive insect barely visible to the eye but potent enough to fell the giants of the eastern United States’ old-growth forests.
Already the tiny bug from Japan, known as the hemlock woolly adelgid (HWA), has killed upward of 95 percent of the hemlocks in Virginia’s Shenandoah National Park. Now they are making their way through the half-million-plus-acre (200,000-plus-hectare) Great Smoky Mountains National Park in North Carolina and Tennessee.
The hemlocks shade streams, keeping water temperatures just right for brook trout(鲑鱼) and other fish. They also house birds such as the black-throated green warbler, solitary vireo, and northern goshawk, all three of which mainly shelter in stands of hemlock trees.
Because of the insect’s broad impact on the entire ecosystem of southern Appalachia, HWA stands to cause wider damage than the American chestnut blight(枯萎病) of the early 1900s. That fungus from Europe killed off the once dominant chestnut trees from the northeast United States to the southern Appalachian Mountains.
In addition, a species related to HWA, the balsam woolly adelgid, has already killed about 90 percent of the mature Fraser fir trees in the Smokies.
Acting Quickly
HWA arrived in the U.S. Pacific Northwest via nursery plants from Japan in 1924. By 1951 the tiny invader had been found in Virginia. Since then the insect has spread to more than 15 U.S. states.
The key to killing the HWA is to catch it early and act quickly. It’s already well established in the Great Smoky Mountains, where Rhea and others are trying to stem the spread of the bugs.
HWA multiply quickly: All of the insects are females that reproduce asexually (无性地), laying several hundred eggs a year. When they get to the nymph, or crawler, stage, they are dormant from about June until October, after which they emerge and establish themselves on trees.
Winds and birds and other animals spread the crawlers through the forest.
HWA crawlers feed on the new growth of hemlocks by piercing the twigs that hold the branches, sucking the sap, and injecting toxic saliva. The needles turn from a deep green to a grayish green and eventually die, depriving the tree of nutrition from photosynthesis.
An infected tree usually dies within five years of initial attack. Infection is signaled by either a white, cottonlike material that appears along a tree’s twigs or by the "baldness" of a tree’s upper branches.
Plans of Attack
In the Pacific Northwest the hemlocks seem to be tolerant of the creatures’ feeding, and in the cold northeast, winters seem to keep them at bay. But in the warm southeast, with weather approximating that of the insects’ native Asian homes, they thrive.
Chemical sprays--such as insecticidal soaps and horticultural oils as well as trunk or soil injections--have helped to kill some of the HWA infestations.
years at most. These methods can’t be used conveniently or safely in remote areas or near the streams where hemlocks grow thickly.
Long term, the best way to control the pests appears to be releasing other insects that feed exclusively on HWA. Scientists have studied HWA in Japan and China and identified three such species. One of them, the Sasajiscymnus tsugae (St) beetle, was released in areas of Great Smoky Mountains National Park in 2002.
Studying what controls a species in its native habitat--including climate, predators, and host resistance--provided clues about which insects to use against HWA, said Kristine Johnson. Based in Gatlinburg, Tennessee, Johnson is a supervisory forester for Great Smoky Mountains National Park.
"Biological control is the only long-term hope to save the trees in the backcountry(穷乡僻壤)," she said. "We have 800 square miles (2,100 square kilometers) of contiguous wilderness. We value the native forest, and it’s entirely worth defending."
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 and plant pathology 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.
Releasing one species of non-native bug to kill another could create ______.
选项
答案
another type of infestation
解析
读完原文,发现Pisky Business下讲了用St bettles来控制HWA这种方法可能带来的风险,而题干正是谈的这种方法,定位Risky Business下的段落,首段即可找到答案
转载请注明原文地址:https://jikaoti.com/ti/CrPFFFFM
0
大学英语四级
相关试题推荐
ThelargeAmericanenergyservicecompany,Enron,failedafewyearsago.IthadbeentheseventhlargestcompanyintheUnited
A、Notlookintohiseyes.B、Stareathim.C、Keepeyecontact.D、Avoideyecontact.C事实题。浏览选项可知,本题考的是“该如何做”,听短文时要对选项所示信息做好标记。原文中关
Top10ReasonsforAfricanAmericanStudentstoGoAbroadBeforegoingabroad,Iwasanarmchairtraveler.Isatatmydesk
Jan.6issue--Theweatheroutsidewasicy,butinside,250journalistsweregatheredinaManhattanofficecomplextoseethela
A、Allowthestudenttotaketheclassthisterm.B、Allowthestudenttotaketheclassnextyear.C、Permitthestudenttogradua
Thebasiccausesareunknown,althoughcertainconditionsthatmayleadtocancerhavebeen______
Turningbackdownthemainstreet,we______ourpaceandmadeourwayrapidlytowardsthehotel.
A、Bothspeakersthinkhalfofthestaffareefficient.B、Thewomanhasafavorableopinionofthestaff.C、Neitherofthemhasa
Everysecond,1hectare(公顷)oftheworld’srainforestisdestroyed.That’sequivalenttotwofootballfields.ThisManningrate
随机试题
苦参的气味是
人民法院审理上诉行政案件,在哪些情况下必须作出发回重审裁定?()
建设单位在签订施工合同后,应将50%的专项费用拨给施工单位。()
简述我国商检机构的基本任务。
经海关确认的溢卸、误卸货物从()3个月内,可由原装载船舶负责人或货物所有人向海关办理退运或进口手续。
根据投资者对( )的不同看法,其采用的证券组合管理方法可大致分为被动管理和主动管理两种类型。
通过对要学习的新材料增加相关信息来达到对新材料的理解和记忆的方法,如补充细节、举出例子,或使之与其他观念形成联想等。这种促进知识保持的方法是()。
党的十九大报告强调必须推进马克思主义中国化时代化大众化,建设具有强大凝聚力和引领力的社会主义意识形态,使全体人民在()上紧紧团结在一起。
虽然我国农村一对夫妇大多生育二胎以上,但几乎所有的年轻人都一拨一拨到城市打工。因此,年轻的高素质移民将不断对冲大城市老龄人口.使人口年龄相对下降或持平,大城市的活力就会保持下去。而在一些地方,老年人支撑农村,已显端倪,甚至可能成为常态。日本的偏僻农村就是前
Inoursociety,workisidentifiedwithajob;itisdoneforanemployerandformoney;unpaidactivitiesdonotcountaswork.
最新回复
(
0
)