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  3. PEST CONTROL (1) Many pest s

PEST CONTROL (1) Many pest s

游客2024-01-02  8
问题                                                 PEST CONTROL
    (1) Many pest species that are native to North America, such as white-footed mice and ground moles, are more nuisance pests and are usually regulated by native predators and parasites. This situation is not true for non-indigenous pests in North America, such as brown rats and cockroaches. After centuries, it is evident that these pests cannot be eradicated. The best that can be done is to introduce pest control measures that will control their numbers.
    (2) An ancient and popular means of pest control is chemical control. For example, the Sumerians used sulfur to combat crop pests, and by the early 1800s such chemicals as arsenic were used to combat insect and fungal pests.
    (3) However, chemical control has its dark side. Chemical pesticides have many unintended consequences through their effects not just on the target species but. on a wide array of non-target species as well, often eliminating them and thereby upsetting the existing food webs, especially through the suppression of native predator species. The surviving pests then rebound in greater numbers than ever.
    (4) Perhaps more insidious is that a pesticide loses its effectiveness because the target species evolves resistance to it. As one pesticide replaces another, the pests acquire a resistance to them all. [A] Some species, notably certain mosquitoes, have overcome the toxic effects of every pesticide to which they have been exposed. [B] Insect pests need only about five years to evolve pesticide resistance, but their predators do so much more slowly. [C] So after the pests develop resistance, pest outbreaks become even more disastrous. [D]
    (5) Farmers long ago observed that enemies of pests act as controls. As early as 300 A.D., the Chinese were introducing predatory ants into their citrus orchards to control leaf-eating caterpillars. Insect pests have their own array of enemies in their native habitats. When an animal or plant is introduced, intentionally or unintentionally, into a new habitat outside of its natural range, it may adapt to the new environment and leave its enemies behind. Freed from predation and finding an abundance of resources, the species quickly becomes a pest or a weed. This fact had led to the search for natural enemies to introduce into populations of pests to reduce their populations.
    (6) Because the serious pest is usually a nonnative species, biological control involves the introduction of a non-indigenous predator or parasite to control the pest. The introduction of the cactus-eating moths, a native of Argentina, into Australia effectively reduced and controlled the rapidly spreading prickly pear, which had been introduced into Australia in 1901.
    (7) But biological control, like chemical control, can backfire. The success of the cactus-feeding moths in controlling prickly pear in Australia encouraged their introduction to several West Indies islands to control prickly pear there. In time the moths made their way to Florida, where they now threaten the existence of several native prickly pear species. The moral is that although using non-indigenous predators as biological controls can be effective, these species possess their own inherent dangers that must be assessed before they are released. They, too, can become alien invaders.
    (8) Because chemical, biological, and other methods used individually are obviously not the solution to pest control, entomologists have developed a holistic approach to pest control, called integrated pest management (IPM). IPM considers the biological, ecological, economic, social, and even aesthetic aspects of pest control and employs a variety of techniques. The objective of IPM is to control the pests not at the time of a major outbreak but at an earlier time when the size of the population is easier to control. The approach is to rely first on natural mortality caused by weather and natural enemies, with as little disruption of the natural system as possible, and to use other methods only if they are needed to hold the pests below the economic injury level.
    (9) Successful IPM requires the knowledge of the population ecology of each pest and its associated species and the dynamics of the host species. It involves considerable field work monitoring the pest species and its natural enemies by such techniques as egg counts and the trapping of adults to acquire information to determine the necessity, timing, and intensity of control measures. These control measures must be adjusted to the situation, which may vary from one location to another. The intensity of control or no control is based on the degree of pest damage that can be tolerated, the costs of control, and the benefits to be derived. [br] Look at the four squares [ ■ ] that indicate where the following sentence could be added to the passage. And the damage will continue until a new pesticide is developed, at which time the cycle will begin anew. Where would the sentence best fit?
选项
答案 D
解析 本题属于插入句子题，句子意为“危害会持续到新的杀虫剂被研发出来，而到那时，新一轮的循环又将重新开始。”由And可知，该句和前一句应说的是相同或相似的内容，属于平行并列关系，所以前一句说的应该也是和危害相关的内容。D处前一句“在害虫产生抗药性之后，其爆发会带来灾难性的后果”总结了上文所述情况。指出其危害，而插入句接着描述这种危害持续的情况，二者逻辑联系紧密，故插入D处最适合。A处前一句说的是害虫对杀虫剂产生抗药性，与插入句的主语the damage关系不密切，逻辑不顺，故不宜放在A处。B处前一句是通过举例来证明害虫对杀虫剂产生抗药性，与插入句关系也不紧密，故也不宜放在B处。C处前一句说的是害虫进化出抗药性的时间比捕食者快，是一种不利于害虫控制的情况，但是也没有提到危害，若把插入句放在此处会显得突兀，故不选C处。
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