GRE阅读题目解析：舞毒蛾

　　P2

　　1

　　The defoliation of millions of acres of trees by massive infestations of gypsy moth caterpillars is a recurring phenomenon in the northeastern United States.

　　美国东北，经常发生数百万英亩森林被大量舞毒蛾幼虫吃光叶子的现象。

　　2

　　In studying these outbreaks, scientists have discovered that affected trees fight back by releasing toxic chemicals, mainly phenols, into their foliage.

　　通过研究这些虫害爆发，科学家们发现受害的树会通过向叶子中释放有毒化学物质，主要是石碳酸，来反击虫害。

　　3

　　These noxious substances limit caterpillars' growth and reduce the number of eggs that female moths lay.

　　这些有毒物质抑制了毛虫生长，并减少了雌蛾产卵数量。

　　4

　　Phenols also make the eggs smaller, which reduces the growth of the following year's caterpillars.

　　石碳酸还使虫卵更小，进而抑制了次年毛虫的生长。

　　5

　　Because the number of eggs a female moth produces is directly related to her size, and because her size is determined entirely by her feeding success as a caterpillar, the trees' defensive mechanism has an impact on moth fecundity.

　　因为一只雌蛾的产卵数与她的体型大小直接相关，又因为她的体型完全由她在幼虫时期的进食充分程度决定，所以树的防御机制对蛾的繁殖有一定影响。

　　(success 此处指 degree or measure of succeeding，成功的程度)

　　6

　　The gypsy moth is also subject to attack by the nucleopolyhedrosis virus, or wilt disease, a particularly important killer of the caterpillars in outbreak years.

　　舞毒蛾也常受到 n 病毒攻击，或者说 w 病，在虫害爆发的年份是特别重要的毛虫杀手。

　　(wilt 枯萎，凋零)

　　7

　　Caterpillars contract wilt disease when they eat a leaf to which the virus, encased in a protein globule, has become attached.

　　病毒被包覆在连接着叶子的蛋白质小球中，毛虫吃掉叶子，就会感染 w 病。

　　8

　　Once ingested by a caterpillar, the protein globule dissolves, releasing thousands of viruses, or virions, that after about two weeks multiply enough to fill the entire body cavity.

　　一旦被毛虫吞下，蛋白质球壳溶解，释放出数以千计的病毒，或病毒粒子，两周后即可繁殖至填满整个虫体。

　　9

　　When the caterpillar dies, the virions are released to the outside, encased in a new protein globule synthesized from the caterpillar's tissues and ready to be picked up by other caterpillars.

　　毛虫死后，病毒粒子被释放到体外，重新被包覆在用死掉的毛虫组织合成的蛋白质小球内，等待感染其他毛虫。

　　10

　　Knowing that phenols, including tannins, often act by associating with and altering the activity of proteins, researchers focused on the effects on caterpillars of ingesting the virus and leaves together.

　　科学家们已知石碳酸，包括单宁酸，通常与蛋白质活性有关且影响其活性，(于是)研究以吞了病毒的毛虫和叶子为重点。

　　11

　　They found that on tannin-rich oak leaves, the virus is considerably less effective at killing caterpillars than when it is on aspen leaves, which are lower in phenols.

　　他们发现富含单宁酸的橡树叶，相较于石碳酸含量较低的白杨树叶，其病毒杀灭毛虫的效果要弱很多。

　　12

　　In general, the more concentrated the phenols in tree leaves, the less deadly the virus.

　　总体来说，树叶中的石碳酸含量越高，病毒越不致命。

　　13

　　Thus, while highly concentrated phenols in tree leaves reduce the caterpillar population by limiting the size of caterpillars and, consequently, the size of the female's egg cluster, these same chemicals also help caterpillars survive by disabling the wilt virus.

　　所以说，尽管树叶中富含的石碳酸通过抑制毛虫体型减少了毛虫数量，进而也减少了雌蛾产卵数，但同样是这些化学成分也帮助毛虫躲过了 w 病的死亡威胁。

　　14

　　Forest stands of red oaks, with their tannin-rich foliage, may even provide caterpillars with safe havens from disease.

　　红栎林的叶子富含单宁酸，甚至可以成为毛虫相对于 w 病的安全避难所。

　　15

　　In stands dominated by trees such as aspen, however, incipient gypsy moth outbreaks are quickly suppressed by viral epidemics.

　　然而在以白杨树为主的林地，舞毒蛾虫害刚爆发就会被病毒的流行压制。

　　16

　　Further research has shown that caterpillars become virtually immune to the wilt virus as the trees on which they feed respond to increasing defoliation.

　　进一步研究已经表明，树木为了应对毛虫啃树叶(而采取的措施，即在树叶中释放石碳酸)，却使毛虫变得免疫 w 病毒。

　　17

　　The trees' own defenses raise the threshold of caterpillar vulnerability to the disease, allowing populations to grow denser without becoming more susceptible to infection.

　　树木自身的防御提高了毛虫受病害的门槛，没有病毒感染的制约，导致毛虫数量上升。

　　18

　　For these reasons, the benefits to the caterpillars of ingesting phenols appear to outweigh the costs.

　　综上可见，毛虫吃石碳酸的好处超过了代价。

　　19

　　Given the presence of the virus, the trees' defensive tactic apparently has backfired. (446 words)

　　鉴于病毒的出现，树木的防御手段显然让树失望了。

　　2. It can be inferred from the passage that wilt disease virions depend for their survival on

　　(A) protein synthesized from the tissues of a host caterpillar

　　(B) aspen leaves with high concentrations of phenols

　　(C) tannin-rich oak leaves

　　(D) nutrients that they synthesize from gypsy moth egg clusters

　　(E) a rising threshold of caterpillar vulnerability to wilt disease

　　选 A

　　有一点也许勉强称得上障碍：

　　depend on / upon sb. / sth. (for sth.) (因某种目的)需要某人 / 某事物

　　depend for their survival on ___ 这种结构只是把 for sth. 提前了而已

　　病毒粒子要生存需要什么?

　　回到句 9：

　　When the caterpillar dies, the virions are released to the outside, encased in a new protein globule synthesized from the caterpillar's tissues and ready to be picked up by other caterpillars.

　　所以选 A 。

　　3.Which of the following best describes the function of the third paragraph of the passage?

　　(A) It resolves a contradiction between the ideas presented in the first and second paragraphs.

　　(B) It introduces research data to support the theory outlined in the second paragraph.

　　(C) It draws a conclusion from conflicting evidence presented in the first two paragraphs.

　　(D) It shows how phenomena described in the first and second paragraphs act in combination.

　　(E) It elaborates on the thesis introduced in the first paragraph after a digression in the second paragraph.

　　选 D

　　非常硬的一道题，读不懂大意就放弃吧。

　　第一段说，树被啃的太疼了，在树叶中释放了 phenols 来对抗虫，让虫发育不良，个小，产卵少，以此来控制虫的数量。

　　第二段说，有一种病毒，能够很高效地杀虫，并描述了杀虫的原理和过程。

　　第三段告诉我们，尽管 phenols 和病毒都抑制虫，但两者却不能很好地合作，以至于虫宁可接受第一种伤害，因为 phenols 不但抑制虫，也让病毒的杀虫效果失败了。

　　A 错在前两段提出的内容没有 contradiction，大家都是杀虫的，看不出矛盾，矛盾是后来相处过程中出现的。

　　B 看到 data 就划掉了。

　　C 类似 A，错在 conflicting 。

　　E 竟然敢说作者 digression 离题了，显然不是人间正道啊。

　　4. Select the sentence in the passage that the author uses as a supporting idea to explicate how gypsy moth caterpillars become immune to the wilt virus.

　　“The trees' own defenses raise the threshold of caterpillar vulnerability to the disease, allowing populations to grow denser without becoming more susceptible to infection.”

　　没啥讲的，不理解答案的反馈给我。

　　For the following question, consider each of the choices separately and select all that apply

　　5.Which of the following statements about gypsy moth caterpillars is supported by information presented in the passage EXCEPT?

　　A Differing concentrations of phenols in leaves have differing effects on the ability of the wilt virus to kill gypsy moth caterpillars.

　　B Female gypsy moth caterpillars stop growing after they ingest leaves containing phenols.

　　C The longer a gypsy moth population is exposed to wilt disease, the greater the likelihood that the gypsy moth caterpillars will become immune to the virus.

　　BC

　　让我们选 EXCEPT 项。

　　A 正确。不同浓度的石碳酸对病毒杀虫能力有不同影响。

　　B 文中没说 stop ，只说了 limit 和 reduce，所以不能确定。

　　C 文中的逻辑是，虫啃树叶，树疼，释放 phenols，phenols 在抑虫同时也让病毒失效，所以虫可以肆无忌惮地继续啃树叶了，只是瘦点少生点但不会死了，最后树叶给啃光。跟 the longer ... the greater ... 的逻辑无关。

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