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 nonindigenous 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.
And ancient and popular means of pest control is chemical. 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.
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 nontarget 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.
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. Some species, notably certain mosquitoes, have overcome the toxic effects of every pesticide to which they have been exposed. Insect pests need not only about five years to evolve pesticide resistance, their predators do so much more slowly. So after the pest develops resistance, pest outbreaks become even more disastrous.
Farmer long ago observed that enemies of pests act as controls. As early as 300 C.E., 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 and 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.
Because the serious pest is usually a nonnative species, biological control involves the introduction of a nonindigenous predator or parasite to control the pest. The introduction of the cactus-eating moth, a native of Argentina, into Australia effectively reduced and controlled the rapidly spreading prickly pear, which had been introduced into Australia in 1901.
But biological control, like chemical control, can backfire. The success of the cactus-feeding moth in controlling prickly pear in Australia encouraged its introduction to several West Indies islands to control prickly pear there. In time the moth made its way to Florida, where it now threatens the existence of several native prickly pear species. The moral is that although using nonindigenous 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.
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 pest not at the time 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 pest below the economic injury level.
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.
1. The word ”evident” in the passage is closet in meaning to
2. What can be inferred from paragraph 1 about nonindigenous pests such as brown rats and cockroaches?
A.Attempts limit the size of their populations have been unsuccessful.
B. They have inhabited North America longer than white-footed mice and ground moles.
C. Their numbers cannot usually be controlled by native predators and parasites.
D. They do not pose as many problems for humans as do white-footed mice and ground moles. Paragraph1 is marked with an arrow [→]
3. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.Chemical pesticides often eliminate species other than the intended target and thereby upset food webs, especially by suppressing native predator species.
B. Native predator species are often eliminated by chemical pesticides that are intended to have consequences for other pests.
C. Chemical pesticides upset existing food webs by eliminating native species and by increasing the number of nonnative predators.
D. The effects of chemical pesticides on a wide array of food webs and native predators are often unintended.
4. In paragraph 5, the author mentions the Chinese use of predatory ants to control pests in order to
A.support the claim that using pests’ natural enemies is a pest control technique that has been known for a long time
B. show that pests’ enemies introduced unintentionally have proved more dangerous than those introduced intentionally
C. help explain that when pests’ enemies find enough resources, they can become pests themselves
D. argue that a pest insect in its native habitat always has a predator in that habitat Paragraph5 is marked with an arrow [→]
5. According to paragraph 5, why is a species likely to become a pest when it is introduced into a new habitat?
A.The species becomes more effective at escaping from its enemies.
B. The species has no natural predators in its new habitat.
C. he species adapts to habitats outside its natural range.
D. The species does not have to compete for resources with other plants and animals. Paragraph5 is marked with an arrow [→]
6. The word ”assessed” in the passage is closet in meaning to
D. dealt with
7. The word ”moral” in the passage is closet in meaning to
8. In paragraph 6, the discussion of the cactus-eating moth and the prickly pear in Australia illustrates which of the following about biological control?
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 nonindigenous 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.. Paragraph6 is marked with an arrow [→]
9. The author discusses the cactus-feeding moth in Florida in order to
A.explain why the prickly pear species that are native to Florida have no indigenous predators
B. show how a predator spreads more rapidly in alien environments than it does in its native environment
C. idicate that a single nonindigenous predator species can be effective against a wide array of nonindigenous pest species
D. argue that controlling pests with nonindigenous predators can have unintended consequences
10. According to paragraph 8, each of the following is a principle of integrated pest management EXCEPT
A.to control pest populations before a major outbreak occurs
B. to first determine if weather and natural enemies are able to control a pest
C. to increase the populations of the pest’s natural enemies during certain seasons of the year
D. to use artificial methods of pest control only when pests begin to cause economic injury Paragraph8 is marked with an arrow [→]
11. The word ”considerable” in the passage is closet in meaning to
B. a large amount of
D. carefully planned
12. According to paragraph 9, each of the following helps to determine how intensely to apply pest control measures EXCEPT
A. how much pest damage can be tolerated
B. the cost of pest control measures
C.what can be gained through pest control measures
D. whether pest control measures have been used before Paragraph9 is marked with an arrow [→]
Paragraph 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. ■Some species, notably certain mosquitoes, have overcome the toxic effects of every pesticide to which they have been exposed. ■Insect pests need not only about five years to evolve pesticide resistance, their predators do so much more slowly. ■So after the pest develops resistance, pest outbreaks become even more disastrous.■
13. 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? Click on a square [■] to add the sentence to the passage.
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong. To review the passage, click on View Text.
Pest control measures vary in their approach and overall degree of success. ● ● ●
1.Biological methods of pest control were introduced by the ancient Sumerians, and chemical control was first used in ancient China.
2.Biological control, for example, the use of natural enemies of pests, has been effective at regulating nonnative pests, though it can also threaten the existence of native species.
3.Integrated pest management is a holistic approach that has been successful at controlling major pest outbreaks in locations where chemical and biological control have already failed.
4.Pesticides are limited in their usefulness because pests quickly become resistant to them, and because they can harm species for which they were not intended.
5.The success of biological and chemical approaches to pest control has been difficult to measure because situations vary significantly from one location to another.
6.Integrated pest management, an approach that consider biological, ecological, economic, and aesthetic aspects of pest control, uses a variety of techniques adjusted to specific situations
托福阅读真题答案 BCAAB CDBDC BDD 246