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  3. Pest Control P1: Pest control is at least as old as agriculture, as there has always been a need to keep crops free from pests.

Pest Control P1: Pest control is at least as old as agriculture, as there has always been a need to keep crops free from pests.

admin2018-10-18  47
问题 Pest Control
P1: Pest control is at least as old as agriculture, as there has always been a need to keep crops free from pests. 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. It is evident that measures must be undertaken to eradicate these pests. One of the most popular methods of pest control is using chemical pesticides, which can be dated back 4,500 years, when the Sumerians used sulfur compounds as insecticides. However, chemical control has its downsides. For one thing, 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. For another, living organisms evolve and increase their resistance to chemical pesticides unless the target population is completely exterminated or is rendered incapable of reproduction.
P2: Importation or classical biological control involves the introduction of a pest’s natural enemies to a new locale where they do not occur naturally. Farmers 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. Early instances of such pest control methods were often unofficial and not based on research, and some introduced species became serious pests themselves. When they adapt to the new environment and leave their enemies behind, these species can quickly get out of control and become a real problem for local populations. Because serious pests are often non-native species, biological control involves the introduction of a non-indigenous predator or parasite to control the pest. For instance, 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.
P3: But biological control, like chemical control, can backfire. The success of the cactus-feeding moth in controlling prickly pear numbers 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 sometimes when a non-native bioagent is introduced to control a non-native pest species, it, in turn, becomes a threat that must be assessed before it can be released.
P4: To make up for the drawbacks of both chemical and biological control methods, entomologists have invented a broad-based approach that integrates practices for economic control of pests, which is known as "Integrated Pest Management" (IPM). IPM involves the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. The objective of IPM is to control the pest 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 pest below the economic injury level.
P5: IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms. Entomologists and ecologists have urged the adoption of IPM pest control since the 1970s IPM allows for safer pest control. This includes considerable field work managing insects, plant pathogens, and weeds, and 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.
P1: Pest control is at least as old as agriculture, as there has always been a need to keep crops free from pests. 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. It is evident that measures must be undertaken to eradicate these pests.
■ One of the most popular methods of pest control is using chemical pesticides, which date back 4,500 years, when the Sumerians used sulfur compounds as insecticides. However, chemical control has its downsides.
■ For one thing, 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. ■ For another, living organisms evolve and increase their resistance to chemical pesticides unless the target population is completely exterminated or is rendered incapable of reproduction. ■
In paragraph 2, the author mentions the Chinese use of predatory ants to control pests in order to
选项 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.
答案A
解析 【修辞目的题】第2句提到很久之前，农民就把害虫的天敌作为一种控制方法。早在公元300年，中国人就引入捕食蚂蚁到他们的柑橘园防治食叶毛虫。所以作者提这个点是为了说明这种方法很久之前就被人们熟知。
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