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  3. PEST CONTROL (1) Many pest s

PEST CONTROL (1) Many pest s

游客2025-02-04  1
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] In paragraph 6, the discussion of the cactus-eating moth and the prickly pear in Australia illustrates which of the following about biological control?
选项 A、Nonnative pests cannot be controlled through biological means once they have begun to spread rapidly.
B、A nonnative pest can sometimes be controlled by the introduction of a nonnative predator.
C、A non-indigenous pest can be controlled only by a predator that comes from the same original habitat as the pest.
D、A native pest can be controlled by either a native or a nonnative predator.
答案 B
解析 本题属于事实信息题。问第6段关于以仙人掌为食的飞蛾和澳大利亚刺梨的描述说明了哪项关于生物控制的事实。第6段第1句提到，带来严重问题的害虫通常是非本地物种，而通过引入非本地捕食者或寄生虫可控制非本地害虫。接下来，作者举出飞蛾和刺梨的例子就是为了说明这一点，故选B项“非本地害虫有时能通过引进非本地捕食者来控制”。A项“非本地害虫一旦迅猛生长，就无法通过生物手段控制”，从飞蛾和刺梨的例子可看出，生物手段有效地控制了害虫的迅猛生长。C项“非本地害虫只能通过引进与它原本栖息地相同的捕食者进行控制”中的only过于绝对，且从第6段第1句的involves可推断，这只是办法之一。D项“本地害虫既能由本地捕食者控制，也能由非本地捕食者控制”，飞蛾和刺梨的例子只能说明非本地捕食者对非本地害虫控制的有效性，无法体现D项。
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