英语四级阅读200篇: Unit 43 passage 1

　　Sometimes when Richard Anderson closes his eyes at night he still has visions of Colorado potato beetles. Ive seen them in the furrows inches thick. Millions of them. You can have potatoes 2 feet high, and they eat them right to the ground, says the 51-year-old farmer. Anderson and his family had grown potatoes on their River head, Long Island, farm since the 1940s, but four years ago they got out of the business-largely because they couldnt control the potato beetle. We were forever spraying, he recalls, but they were just immune.

　　For farmers like Anderson, pesticide use has become not the solution but a cause of many pest problems. Rachel Carson predicted as much 30 years ago in Silent Spring, though the public paid little notice amid the furor her book sparked over pesticides ecological and health effects. In recent years, however, pesticides shortcomings have grown harder to ignore in light of mountain pesticide resistance and destruction of beneficial insects. In fact, a growing number of agricultural experts now argue that reducing pesticide use can actually decrease pests. Pest control has reached a turning point, says pest control expert Robert Metcalf of the University of Illinois at Urbana.

　　When DDT, the first widely used synthetic pesticide, hit the market in 1946, it looked like the silver bullet that would wipe out insect pests forever. Before DDT, American farmers lost about a third of their crops each year to insects, weeds and disease. Today, with an annual pesticide bill exceeding $ 4 billion, farmers still lose the same one-third share a loss that mounts into the tens of billions of dollars each year.

　　Chemical pest control has grown steadily more difficult because of a growing number of pesticide-resistant insects and weeds. Resistance is biologically inescapable: Each time a farmer sprays a field, the few bugs genetically able to tolerate the poison stand the best chance of surviving to produce the .next generation of increasingly resilient insects. Its just accelerated evolution. Darwin would be pleased, says Metcalf. In 1948 just 14 species of insects were resistant to one or more pesticides; more than 500 are resistant today. Even the bacterial insecticide Bacillus thuringiensis, or Bt, once touted as practically resistance proof because of its complexity, is beginning to lose its effectiveness on a few agricultural pests.

　　More ominous , several important insects have developed resistance to every major insecticide. In the state of Gujarat in India, for instance, the mosquitoes that transmit malaria are resistant to every affordable insecticide, and malaria rates are surging. Similarly in the northeastern United States, the Colorado potato beetle has become resistant to at least 15 chemicals, leaving potato growers dependent on a compound not yet formally approved for potatoes.

　　Pesticides also create new pests because they destroy the spiders, wasps and predatory beetle that naturally keep most plant-feeding insect populations in check. The brown plant hopper that plagued Indonesian rice fields in the 1970s and 80s was not a serious problem until 1970, shortly after heavy insecticide use began. In the United States, such major pests as spider mites and cotton bollworm were nuisances at most until spraying decimated their predator.

　　Even so many farmers feel they would have a tough time staying in business without pesticides. Quick and direct pesticides help protect farmers from ruinous losses caused by a sudden pest outbreak. They also allow use of more pest-prone practices like larger fields planted to a single crop so that farmers can specialize in fewer crops, maximizing efficiency. And though a small minority of farmers have successfully abandoned pesticides altogether most experts and even some organic farmers admit that quitting cold turkey is not feasible for every crop or in every region of the country.

　　Not surprisingly, there is new interest in an option that has been around for decades; a multi-pronged strategy known as integrated pest management that many experts say can reduce pesticide use by 50 percent or more without lowering yields. Farmers choose among a variety of techniques including rotating crops, planting pest-resistant varieties and encouraging the build-up of natural enemies to prevent pest outbreaks. Pesticides are used as little as possible and only if non-chemical measures fail to keep pests below damaging levels.

　　Researchers continue adding to the IPM arsenal. One new technique, pioneered by Metcalf and approved last month by the U. S. Environmental Protection Agency, uses poison bait laced with a chemical from the host plant that entices the pests to eat the poison; insects that dont naturally feed on the crop ignore the chemical cue and escape the poison. West Coast artichoke and cranberry growers are experimenting with tiny roundworms to kill insects. Biologists at Cornell University are developing a potato variety with sticky leaf hairs that repel beetles and aphids, and entomologists at Washington State University are experimenting with a common potato-field weed that beetle find so tasty they ignore nearby potatoes.

　　Many IPM programs have been astonishingly successful. After years of heavy pesticide use had only worsened the brown plant hopper problem in rice fields, the Indonesian government in 1986 banned dozens of insecticides and invested millions of dollars in IPM training for farmers. In the next four years, the countrys pesticide use fell 50 percent, rice yields rose 12 percent and the brown plant hopper problem faded away. In the Rio Grande Valley of Texas, IPM has allowed cotton farmers to go from 12 sprayings per year to just four. Besides reducing risks to wildlife or human health, such efforts carry a less obvious benefit: resistance develops more slowly when pests are zapped less often.

　　Fed by success stories like these, interest in IPM programs is gradually spreading throughout mainstream American agriculture. Farm organizations, environmentalists and even chemical companies have joined forces to push for wider use of IPM, though a few critics charge that some of this support is little more than lip service to justify continued reliance on pesticides. In the governmental ranks, the U. S. Department of Agriculture and the Environmental Protection Agency not previously the most cordial of partners on pesticide issues, according to IPM program coordinator Michael Fitzner of the USDA Extension Service have begun cooperating on IPM research and policy.

　　Nevertheless, IPM has been slow to appear in farmers fields. Although it has become the norm for a few crops such as cotton, citrus, apples and tomatoes only about a quarter of high-acreage field crops like corn, wheat and soybeans have made the transition. Most experts blame a shortage of IPM specialists and a lack of funds for educating farmers in the new techniques. In addition, economic constraints often hinder the switch to IPM. In northeastern states, for example, many growers say they cant afford to rotate potatoes with crops like soybeans or wheat an effective way to control potato beetles because land rents are too high to make these lower-grossing crops profitable.

　　1. All pesticides, from the first widely used DDT to bacterial insecticide Bt, have gradually lost their effectiveness.

　　2. American farmers lose the same amount of crops each year as they did before the use of DDT.

　　3. Pests who can survive pesticides produce more adaptable young generations, which quickens the speed of evolution of pests.

　　4. In India, The number of some pests grew rapidly and became much more serious problems because their natural enemies were killed by pesticides.

　　5. Many farmers believe that it is possible to stop using pesticides without affecting their business.

　　6. Despite the unsatisfactory development, IPM programs have attracted growing attention in American agriculture.

　　7. IPM is and will be the only answer to the pesticides problems now and far in the future.

　　8. IPM stands for______.

　　9. In Indonesia four years after the ban on dozens of insecticides in 1986, the brown plant hopper problem______.

　　10. The numbers of species resistant to one or more pesticides in 1948 and today were

　　答案：

　　1. Y 2. N 3. Y 4. N 5. N 6. Y 7. NG

　　8. integrated pest management 9. faded away 10. 14 and more than 500