托福阅读背景材料(342)：处理害虫方法

　　托福阅读背景知识/材料之处理害虫方法，更多托福阅读背景材料/知识尽在新东方在线托福考试频道！

　　2014年5月25日托福阅读真题再现：

　　讲得是pest的问题，如何处理害虫。

　　先讲了一个例子好像是美国西南部，具体记不清了，其实是为了引出 chemical 方法 ，就是杀虫剂pesticide，而且还讲了杀虫剂的负作用，会对native的一些物种造成预想不到的损伤。同时pest产生耐药性的时间大约5年，远短于研制出新的pesticide所需要的时间。(就是说这方法有明显缺陷，好引出下面的方法，你们懂得!!!肯定有题的嘛...)

　　然后就讲了biological方法，引进pest的天敌，因为多数顽固的pest其实是外来物种，之所以成为pest就是没有天敌。这里举了中国古代的一个例子，知道例子的功能就好。 (有题)然后这提到了一些不足，细节记不太清楚了。

　　最后来到了终极大招，一个叫IPM的方法让害虫们明白!!!其实就是一种integrated的什么方法，综合考虑各种因素，什么经济啊，生物学啊，如果不得不用杀虫剂要控制剂量啊等等(有排除题)。其实我觉得不算新方法，但是就是综合考虑，然后就有了IPM这样一个酷炫的名字。

　　解析：

　　本篇文章讲解了处理害虫的不同方法。理解文章时按照不同的处理方法梳理文章的结构，不同的方法要把握住作者关于其优点和缺点的介绍，不同的方法的不同特点为文章出题的题点。

　　Insects become resistant to chemical insecticides very rapidly—it can happen in as few as five generations. This is natural selection at work.

　　The problem is that an insecticide never kills all of its intended victims. If even a few insects survive, they will reproduce. These surviving insects will produce two types of young—those that are resistant to the spray, and those that are not. The non-resistant insects will be killed in the next spraying, but those that are left reproduce. At each generation, the number of naturally resistant insects in the population increases.

　　An individual insect does not become resistant during its lifetime. It is born either resistant or non-resistant, and it is the population as a whole that gradually becomes resistant to the pesticide over time. The Bt toxins become ineffective, and the benefits of using them (less toxicity to non-target species) disappear.

　　As this occurs, a new pesticide must be developed. Over time, populations of insects can become resistant to more and more pesticides. As a result, humans need to make different pesticides that are generally stronger.

　　Organic farmers have used Bt on their crops for a number of years. They are concerned that the increased use of the Bt toxin could speed up the development of resistant insect populations.

　　Entomologists know that controlled, laboratory experiments with generations of insects cannot be easily reproduced in the field. How the resistant insects breed with refuge insects, and over what time frames, will determine the success of this technology.

　　These concerns are balanced by concerns that existing pesticide practices can be much more dangerous for non-target insect species than insect-resistant crops. Conventional non-selective pesticides kill many non-target insects. By reducing the number of sprays needed, insect-resistant crops help to preserve beneficial predator insects and simplify management decisions.