A small number of the forest species of lepidoptera (moths and butterf

Question

A small number of the forest species of lepidoptera (moths and butterflies, which exist as caterpillars Line during most of their life cycle) exhibit regularly recurring patterns of population growth and decline—such fluctuations in population are known as population cycles. Although many different variables influence population levels, a regular pattern such as a population cycle seems to imply a dominant, driving force. Identification of that driving force, however, has proved surprisingly elusive despite considerable research. The common approach of studying causes of population cycles by measuring the mortality caused by different agents, such as predatory birds or parasites, has been unproductive in the case of lepidoptera. Moreover, population ecologists’ attempts to alter cycles by changing the caterpillars’ habitat and by reducing caterpillar populations have not succeeded.  In short, the evidence implies that these insect populations, if not self-regulating, may at least be regulated by an agent more intimately connected with the insect than are predatory birds or parasites .

Recent work suggests that this agent may be a virus. For many years, viral disease had been reported in declining populations of caterpillars, but population ecologists had usually considered viral disease to have contributed to the decline once it was underway rather than to have initiated it. The recent work has been made possible by new techniques of molecular biology that allow viral DNA to be detected at low concentrations in the environment. Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera in part because the viruses themselves follow an infectious cycle in which, if protected from direct sun light, they may remain virulent for many years in the environment, embedded in durable crystals of polyhedrin protein. Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells.Late in the course of the infection, millions of new virus particles are formed and enclosed in polyhedrin crystals. These crystals reenter the environment after the insect dies and decomposes, thus becoming available to infect other caterpillars.

One of the attractions of this hypothesis is its broad applicability. Remarkably, despite significant differences in habitat and behavior, many species of lepidoptera have population cycles of similar length, between eight and eleven years. Nuclear polyhedrosis viral infection is one factor these disparate species share.   1 
RC00120-06.

1. It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to

(A) develop an explanation for the existence of lepidoptera population cycles
(B) identify behavioral factors in lepidoptera that affect survival rates
(C) identify possible methods for controlling Lepidoptera population growth
(D) provide evidence that lepidoptera populations are self-regulating
(E) determine the life stages of lepidoptera at which mortality rates are highest

2 
RC00120-05.

2. The primary purpose of the passage is to

(A) describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera
(B) present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera
(C) present a hypothesis about the driving force behind population cycles in lepidoptera
(D) describe the fluctuating patterns of population cycles in Lepidoptera
(E) question the idea that a single driving force is behind population cycles in Lepidoptera

3 
RC00120-02

3. According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases--

(A) were not widely prevalent among insect populations generally
(B) affected only the caterpillar life stage of lepidoptera
(C) were the driving force behind Lepidoptera population cycles
(D) attacked already declining caterpillar populations
(E) infected birds and parasites that prey on various species of lepidoptera

4 
RC00120-03.

4. According to the passage, nuclear polyhedrosis viruses can remain virulent in the environment only when

(A) the polyhedrin protein crystals dissolve
(B) caterpillar population are in decline
(C) they are present in large numbers
(D) their concentration in a particular area remains low
(E) they are sheltered from direct sunlight

5 
RC00120-04.

5. It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus

(A) is exposed to direct sunlight
(B) is attractive to predators
(C) cannot infect caterpillars' cells
(D) cannot be ingested by caterpillars
(E) cannot be detected by new techniques of molecular biology

6 
RC00120-01.

6. Which of the following, if true, would most weaken the author’s conclusion in lines 18-22?

(A) New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
(B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
(C) Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
(D) Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
(E) Viral disease is typically observed in a large proportion of the lepidoptera population.

JOURNAL ARTICLE 
  Population Outbreaks in Forest Lepidoptera  
Judith H. Myers
American Scientist
Vol. 81, No. 3 (May-June 1993), pp. 240-251
Published by: Sigma Xi, The Scientific Research Honor Society
Stable URL:  https://www.jstor.org/stable/29774919 
Page Count: 12

OG 2019 ID's
RC00120-05
RC00120-06
RC00120-01
RC00120-02
RC00120-03
RC00120-04

GMATNinja · Accepted Answer

This question asks us to flex our CR muscles, but let's first take a moment to nail down the structure and purpose of this passage:

In paragraph 1, the author explains that a small number of lepidoptera species exhibit population cycles, and states that the driving force behind these cycles is difficult to identify. The author concludes that this driving force may be intimately connected to the insect itself, rather than being connected to the insect's predators or parasites. 
  In paragraph 2, the author presents recent work, which suggests that this driving force (a.k.a. the agent regulating population cycles) may be a virus. 
  In paragraph 3, the author notes that the virus hypothesis is attractive because it seems broadly applicable across different lepidoptera species.

OK, now let's revisit the conclusion being highlighted:

The author concludes that whatever is regulating the population cycle is closer to the insect than it is to predatory birds or parasites. Here's how the author reaches this conclusion:

Studying predatory birds and parasites, thought to be potential agents, has been unproductive in the case of lepidoptera. 
  Recent study of viral disease, thanks to new techniques of molecular biology, has identified nuclear polyhedrosis viruses as a more likely agent. 
  Polyhedrosis viruses follow an infectious cycle that is intimately linked to lepidoptera, in which lepidoptera ingest the virus in the form of crystals, incubate new virus particles within their bodies, and release these crystals back into the environment upon dying.

If we're looking to weaken this conclusion, we need an answer choice that either:

contradicts what we've read about this link between polyhedrosis viruses and lepidoptera, or 
 delivers evidence that some other regulating agent is even more likely to be the driving force of these population cycles.

Now let's use process of elimination to go through all five choices.

This choice actually strengthens the conclusion, because it adds evidence that other potential agents (predatory birds and parasites) have significantly decreased in number in recent years. This reinforces what the author stated plainly in paragraph 1. Eliminate (A).

This choice introduces new evidence that the regulating agent we're all looking for might be intimately linked to the habitats of lepidoptera, after all. Most importantly, this choice tells us that whatever these experiments did to habitats, that action  definitely resulted in the shortening of lepidoptera population cycles . We'll keep choice (B) because it provides proof that another agent--habitat--can regulate population cycles.

Knowing that the nuclear polyhedrosis virus is present in a number of predators and parasites doesn't change anything we've read about the nuclear polyhedrosis virus and its link to lepidoptera. The author's conclusion does not depend on this virus existing only in lepidoptera. And the language of this answer choice doesn't include any dismissal of the intimate link between polyhedrosis viruses and lepidoptera. It simply points out that the virus is also present in predators and parasites of lepidoptera.

(C) doesn't contradict the impact of nuclear polyhedrosis viruses or provide an alternative agent, so we'll eliminate (C).

Choice (D) does identify a potential alternative agent: weather. However, the logical statement made here is quite weak. (D) tells us that it's  difficult  to assess the effects of weather on lepidoptera population cycles. So even if it's possible for weather to affect these population cycles,  we have no way of confirming whether that effect is actually taking place .

Likewise, I could say, "It's difficult to assess the effects of the lunar cycle on lepidoptera," but this wouldn't make me jump up and say that lunar cycles are likely to be more of a driving force of lepidoptera population cycles than nuclear polyhedrosis viruses. We're not interested in  hypothetical  effects that are difficult to assess. We're interested in proof that an alternative agent is truly at work. That's why we eliminate (D).

This choice doesn't affect the conclusion. Much like Choice (C), it tells us a little more about the presence of viral disease in lepidoptera populations, but it doesn't mention polyhedrosis viruses and doesn't provide evidence of any alternative agent regulating population cycles. Eliminate (E).

Whew! This may have taken me an entire population cycle to write. (Yes, more bad Dad jokes. I'm practicing them. There's no "negative kudos" button, so you're stuck with them.) After all of that, (B) is the only choice that presents evidence of a regulating agent that is NOT intimately linked to the  insect  (instead, the agent is linked to the insect's  habitat ). So we keep (B) and move on.

I hope this helps!

GMATNinja · Answer

The author describes the behavior of the nuclear polyhedrosis virus (let's just say "virus") inside and outsides its polyhedrin protein crystals (let's say "crystals") in the second paragraph.

Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera in part because the viruses themselves follow an infectious cycle in which, if protected from direct sun light, they may remain virulent for many years in the environment, embedded in durable crystals of polyhedrin protein. Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells. Late in the course of the infection, millions of new virus particles are formed and enclosed in polyhedrin crystals. These crystals reenter the environment after the insect dies and decomposes, thus becoming available to infect other caterpillars.

Let's break down this process to confirm what exactly happens to the  virus  and its surrounding  crystals :

The virus is embedded in crystals. The crystals protect the virus from direct sun light. 
  After a caterpillar ingests the crystals, the crystals dissolve. 
  Once the crystals dissolve, the virus infects the caterpillar. 
  At the end of the infection, millions of new virus particles pop up and are enclosed in new crystals. 
  After the caterpillar dies and decomposes, these new crystals reenter the environment.

We're looking for the choice that reflects what the virus can or can't do while it's inside the crystals. And we'll eliminate any choice that doesn't fit into the picture we've just spelled out.

This is the opposite of what we've read. The crystals protect the virus from direct sunlight. Eliminate (A).

When discussing the virus and its crystals, the author never mentions a predator that would treat the crystals or the virus as prey. Choice (B) mixes up the topics of the first and second paragraph. Eliminate it.

This looks good! We know that infection occurs  after the crystals dissolve . This implies that  before the crystals dissolve , the virus cannot infect caterpillars' cells. Let's keep (C) around and see if the remaining choices are better.

This is totally off the mark. We're told explicitly that caterpillars ingest the crystals. Eliminate (D).

This also contradicts evidence in the passage. Just before the author gets into the process of how the virus infects caterpillars, the author mentions that "The recent work has been made possible by new techniques of molecular biology that allow viral DNA to be detected at low concentrations in the environment."

This implies that new techniques of molecular biology are certainly able to detect the virus, whether it's inside or outside the crystals. It seems these new techniques are what have allowed researchers to describe the process of ingestion, dissolution, infection, replication, and reentry into the environment. So let's eliminate (E) as well.

I hope this helps!

icandy · Answer

Here is what I am confused about

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

So what is the conclusion in these 5 lines?

Pop Cycles are not completely self regulated and not caused by birds or insects.

The fact that alteration cycles have not succeeded is an evidence

While I agree that B attacks the evidence, I dont think it weakens the conclusion one way or the other.

With C it is saying that the virus from predators/birds is actually the cause. So Pop cycles are possibly caused by virus by birds/predators. The later part of the passage clearly establishes that virus is transmitted by birds and predators.

So why is C wrong and B is correct? is it because the NPV is not introduced in the passage by the lines of 25-30??

Technext · Answer

25) tions have not succeeded. In short,
the evidence implies that these insect
populations, if not self-regulating, may
at least be regulated by an agent more
intimately connected with the insect than
(30) are predatory birds or parasites.

Which of the following, if true, would most weaken the author’s conclusion in lines 25-30?

--------------------------
 Explanation :
 
 A . New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years. ---> Irrelevant.
 
 B . New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles. ---> The author mentions in the excerpt that there is some other agent that controls the insect population. He concludes this on the basis of info present in lines 15-25. But this option makes clear that  there were still some untried ways , which actually resulted in some  concrete findings  (shortening of lepidoptera population cycles).

I think,  nitya34  is also trying to convey the same reasoning.
 
 C . Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera. ---> This may strengthen the argument by assuming virus as a more intimately connected regulatory agent. (Refer line 31: …..Recent work suggests that this agent may be a virus.....)

icandy: Can you please point to the line where it clearly establishes that virus is transmitted by birds and predators?

Anyways, IMO, even if it’s mentioned that the virus is transmitted by birds and predators, it’ll not be the correct answer because viruses are just piggybacking on birds and predators.  Viruses  are the actual agents not  birds and predators .

So, I ruled out option C.

D . Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles. ---> Inconclusive. This option states that assessing the effect of weather (in case, it could have acted as an agent) on lepidoptera population cycles has proved to be a problematic task.  As no results have been mentioned , we cannot conclude anything.
 
 E . Viral disease is typically observed in a large proportion of the lepidoptera population. ---> Irrelevant.
--------------------------

I also go for option  B .

Hope that helps.

Regards,
Technext

tronghieu1987 · Answer

1. Which of the following, if true, would most weaken the author’s conclusion in lines 25- 30 (bold lines)? 
The conclusion is the insect population maybe at least be regulated by an agent more intimate.... It is drawn based on 2 premises:
- The approach of measuring mortality caused by predatory birds or parasites does not work;
- The experiments to change caterpillar's habitat and population don't work either.

So in order to weaken the conclusion, we need to break the link between the conclusion and one of 2 above premises.

A. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years. 
Does not affect the conclusion. The number of those birds and parasites decreased, but the lepidoptera population fluctuated -> strengthen the conclusion.

B. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles. 
CORRECT! It is not that the experiments don't work, but the untried ones do -> the link between the conclusion and the 2nd premise is broken.

C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera. 
Strengthen the conclusion when citing a possible cause related to the insect itself.

D. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles. 
This is a contender. I think it affects the conclusion on a certain level. Need someone's explanation for eliminating this choice.

E. Viral disease is typically observed in a large proportion of the lepidoptera population. 
Same as C. It supports the conclusion.

phuulinh225 · Answer

For question number 5, I chose E because I could not find any right answer choice A to D. But OA is C. Anyone could help explain why C? Many thanks

RC00120-04. It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus (A) is exposed to direct sunlight (B) is attractive to predators (C) cannot infect caterpillars' cells (D) cannot be ingested by caterpillars (E) cannot be detected by new techniques of molecular biology

LeenaSai · Answer

Can anyone explain the se one question ?

“ It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to ????”

I thought it’s option C

Posted from my mobile device

KaranB1 · Answer

LeenaSai

To answer the question lets first understand the passage.

Para 1- explains what is population cycle. Then para moves on to state that among various factors anyone factor must be dominant that causes population cycle.
Despite considerable research finding that one factor has not been very easy. Common approach of analysing parasite and predators has been unproductive and so are others.
If population cycle is not self regulating then there must be some factor intimately connected that causes the phenomenon.

In Para2- Nuclear polyhedrosis viruses are hypothesized to be that factor and reasons to believe the hypothesis are described.

Para3- Provides additional supporting reasons to believe the hypothesis.

Now, coming to the question at hand.

Option C is about "possible methods for controlling Lepidoptera population growth". This paraege is nowhere concerned or discusses about methods for controlling Lepidoptera population growth.

Option A is indeed the correct answer choice as predatory birds or parasites was measured in an attempt to find the dominant factor that regulates lepidoptera population cycles.

I hope this explanation helps.

admission2020 · Answer

RC00120-05.The primary purpose of the passage is to
(A) describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera
(B) present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera
(C) present a hypothesis about the driving force behind population cycles in lepidoptera
(D) describe the fluctuating patterns of population cycles in Lepidoptera
(E) question the idea that a single driving force is behind population cycles in Lepidoptera

I got confused between B and C. Can someone explain why B is wrong.

GMATNinja

daagh · Answer

Q1. 
RC00120-06. It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to

(A) develop an explanation for the existence of lepidoptera population cycles
(B) identify behavioral factors in lepidoptera that affect survival rates
(C) identify possible methods for controlling Lepidoptera population growth
(D) provide evidence that lepidoptera populations are self-regulating
(E) determine the life stages of lepidoptera at which mortality rates are highest

As far as I see, Q1 is not about any viral connection. It is about population cycles and the reason for those cycles before anyone knew how they occurred. The virus is only figuring in the later part of the story. It has nothing to do with the earlier attempts to know why the cycles occurred. 
I didn't get your point on the difference between a CR rationale and RC rationale. There can be only one rationale. What holds true for CR must be true for RC too.

GMATNinja · Answer

The key to answering primary purpose questions is to understand the purpose of each piece of the passage, and determine how these pieces connect to one another. This passage breaks down nicely into paragraphs, so let's go through each one:

Paragraph 1: The author introduces the idea of population cycles, and then states that attempts to determine the driving force behind these cycles have been "unproductive." These attempts focused on several different factors -- predatory birds and parasites, changes in habitat, etc. 
 Paragraph 2: The author introduces another potential "driving force" -- viruses. He/she then explains the mechanisms behind this theory 
 Paragraph 3: The author provides additional support for the theory that viruses are the driving force behind population cycles.

When taken together, it is clear that the author's primary purpose is to introduce and explain the evidence behind a new theory -- the information in the first paragraph is included to provide additional context for the new hypothesis. Let's see how that stacks up against the answer choices in question:

There are a couple of issues with this answer choice. First the author does not refute a " particular  theory" -- he/she states that inquiries into  several  potential theories have been unproductive. In addition, the author's primary purpose is not to  refute  these other theories. Instead, he/she wants to discuss a  new  theory (that viruses are the driving force behind population cycles). For these reasons, (B) is out.

Here we go! The "hypothesis" is that viruses are the driving force behind population cycles in lepidoptera. While the author does discuss other theories, he/she includes these in the passage to provide context for the virus hypothesis -- so we can say that the "primary purpose" of the passage is to present the new hypothesis.

I hope that helps!

adkikani · Answer

GMATNinja   VeritasKarishma   MentorTutoring

Is the highlighted portion rendering this option incorrect?
This answer choice  seems soo correct.  
describe new techniques: yes author talks about virus
that may help to determine the driving force behind population cycles in lepidoptera: yes , earlier factors (driving forces mentioned in para-1) did not help to understand population cycles, but virus does.

AndrewN · Answer

Hello,  adkikani . I would argue that the whole part up to  techniques  is what makes the answer definitively incorrect, rather than a single word. Keep in mind, a  primary purpose  question is taking into account the whole passage, not simply the  what  of its contents, but its authorial presence as well. In this case,  describe the development of new techniques  begs the question,  What are these new techniques, and is the passage  describing  them, rather than simply presenting them?  For this to be the answer, I need to know what these techniques are, and I need to see them permeate the passage, rather than just get a passing mention in one paragraph or another. The nail in the coffin of this answer choice comes from the middle of the second paragraph:

The recent work has been made possible by  new techniques  of molecular biology that allow viral DNA to be detected at low concentrations in the environment.

I put a finger on these  new techniques , but nowhere do I get a description of them, and the passage is certainly not centered on them. Rather, the next sentence lays out the course of the rest of the passage:

Nuclear polyhedrosis viruses are hypothesized to be the driving force behind population cycles in lepidoptera...

Paragraph one presents the issue:

Although many different variables influence population levels, a regular pattern such as a population cycle seems to imply a dominant, driving force. Identification of that driving force, however, has proved surprisingly elusive despite considerable research.

The information in paragraph two above serves to develop the passage from this paragraph one backbone. That is, perhaps the hypothesis that is mentioned is the  driving force  in question. Altogether, the clues point to (C) as being the hardest answer to argue against. (The question took me 38 seconds to answer correctly. Strong, conclusive, specific language is often easier to debate than more cautious and vague language, and  main idea  questions in particular tend to prefer the latter.)

I hope that helps. Please let me know if you have further questions.

- Andrew

KarishmaB · Answer

The passage discusses no technique. Note that the passage introduces the idea that lepidoptera exhibit population cycles and then goes on to say that the driving force has not been identified. Then the passage tells us that new tech has allowed us to see that the agent may be a virus and then it goes on to explain this hypothesis. The only mention of new tech is that it helped discover a probable agent. The whole story is about that agent - the virus, not about the techniques. You would see a lot more mention of scientific methods if tech were discussed.

homersimpsons · Answer

OE

Q1. It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to
A. develop an explanation for the existence of lepidoptera population cycles
B. identify behavioral factors in lepidoptera that affect survival rates
C. identify possible methods for controlling lepidoptera population growth
D. provide evidence that lepidoptera populations are self-regulating
E. determine the life stages of lepidoptera at which mortality rates are highest
 Inference 
The passage states that mortality caused by various agents, birds and parasites among them, was measured because this was the common approach to studying causes of population cycles. This in turn suggests that those scientists engaged in such measuring in the case of lepidoptera were attempting to come up with a definitive explanation for why those lepidoptera population cycles occurred.
A.  Correct . Measuring mortality caused by various agents was part of the attempt to determine the driving force behind lepidoptera population cycles.
B. The passage does not indicate that behavioral factors in lepidoptera are related to their mortality as caused by agents such as predatory birds or parasites.
C. The passage is concerned not with controlling lepidoptera population growth, but rather with determining why population cycles occur.
D. According to the information in the passage, scientists sought to measure mortality caused by particular agents in order to determine the driving force behind lepidoptera population cycles. In suggesting that mortality caused by these agents is not that force, the measurements may have indicated that the cycles could be self-regulating, but they were not undertaken in order to provide such evidence.
E. The passage discusses mortality primarily in the caterpillar stage and does not suggest that any research was directed toward comparing caterpillar mortality rates with mortality rates in other life stages of the insects.
 The correct answer is A.

Q2. The primary purpose of the passage is to
A. describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera
B. present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera
C. present a hypothesis about the driving force behind population cycles in lepidoptera
D. describe the fluctuating patterns of population cycles in lepidoptera
E. question the idea that a single driving force is behind population cycles in lepidoptera
 Main idea 
This question depends on understanding the passage as a whole in order to identify its purpose. The first paragraph defines population cycles of lepidoptera and discusses some ways those cycles have been studied. It suggests that a particular agent may regulate these cycles. The second paragraph describes a candidate for this agent: nuclear polyhedrosis viruses. The third paragraph explains why this hypothesis is compelling.
A. The passage mentions new techniques in molecular biology, but it does so in order to explain why a particular candidate for the agent behind population cycles has come to light.
B. The theory the passage presents is that there is a driving force behind lepidoptera population cycles. It does not refute this theory; rather, it offers a convincing case for nuclear polyhedrosis viruses as that force. It also discusses some previous approaches to seeking plausible hypotheses but does not focus on refuting any particular hypothesis.
C.  Correct.  The passage is primarily concerned with presenting the hypothesis that nuclear polyhedrosis viruses are the driving force behind lepidoptera population cycles.
D. The first paragraph describes the fluctuating patterns of lepidoptera population cycles, but it does so to explain what population cycles are, so that it can then go on to attempt to account for those cycles.
E. The passage is concerned with making a case for nuclear polyhedrosis viruses as the driving force behind at least some lepidoptera population cycles, not with questioning the idea that there is a driving force.
 The correct answer is C.

Q3. According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases
A. were not widely prevalent among insect populations generally
B. affected only the caterpillar life stage of lepidoptera
C. were the driving force behind lepidoptera population cycles
D. attacked already declining caterpillar populations
E. infected birds and parasites that prey on various species of lepidoptera
 Supporting Idea 
This question addresses what the passage states directly about population ecologists’ beliefs regarding viral diseases prior to the discovery of new viral DNA–detection techniques. The second paragraph of the passage states that these ecologists believed viral disease contributed to population decline that was already underway rather than initiating it.
A. The second paragraph states that viral disease had been reported; thus, population ecologists were aware of its existence in insect populations. The passage is consistent with ecologists having believed that it was prevalent.
B. The passage focuses mainly on the caterpillar life stage of lepidoptera, but there is nothing to suggest that scientists held particular beliefs regarding viral diseases’ restriction to that life stage.
C. It is after, not before, the discovery of new techniques for detecting viral DNA when populations ecologists came to believe that such diseases were the driving force behind the population cycles.
D.  Correct . As stated in the passage, population ecologists believed that viral diseases contributed to already occurring population decline.
E. The passage does not discuss whether viral diseases may infect any lepidoptera predators.
 The correct answer is D.

Q4. According to the passage, nuclear polyhedrosis viruses can remain virulent in the environment only when
A. the polyhedrin protein crystals dissolve
B. caterpillar populations are in decline
C. they are present in large numbers
D. their concentration in a particular area remains low
E. they are sheltered from direct sunlight
 Supporting Idea 
The passage states in the second paragraph that these viruses remain virulent for many years if they are protected from direct sunlight. They are embedded in crystals of polyhedrin protein.
A. The viruses remain virulent partially because of their being contained in polyhedrin protein crystals.
They would most likely not remain virulent if those crystals dissolved.
B. The viruses remain virulent even when caterpillar populations are not in decline; that is how the viruses initiate new population declines.
C. According to the passage, viral DNA has been detected in the environment at low concentrations, yet the viruses are still virulent. Thus, they need not be present in large numbers.
D. Nothing in the passage indicates that the concentration of these viruses must be low for them to be virulent.
E.  Correct.  The passage says that if the viruses are protected from direct sunlight, they remain virulent for many years. The context strongly suggests that if they are not so protected, they do not remain virulent.
 The correct answer is E.

Q5. It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus
A. is exposed to direct sunlight
B. is attractive to predators
C. cannot infect caterpillars’ cells
D. cannot be ingested by caterpillars
E. cannot be detected by new techniques of molecular biology
 Inference 
The passage indicates that the polyhedrin protein crystals protect the nuclear polyhedrosis virus when it is in the environment. When a caterpillar ingests those crystals, they dissolve. That releases the virus, whereupon it infects the caterpillar’s cells. Thus it is reasonable to infer that the virus must be released from the crystals before it can infect the caterpillar.
A. The passage states that nuclear polyhedrosis viruses remain embedded in polyhedrin protein crystals if protected from direct sunlight, not that the virus is exposed to light when it is in the protein crystals.
B. Nothing in the passage indicates that any organism preys on the virus itself or that it attracts predators to caterpillars that it infects.
C.  Correct.  The virus must be released from the crystals before it can infect caterpillars’ cells.
D. The passage states that caterpillars ingest the polyhedrin protein crystals.
E. According to the passage, new techniques of molecular biology enable the detection of viral DNA in the environment. The nuclear polyhedrosis virus persists in the environment inside protein crystals.
The passage suggests that the new techniques are able to detect the virus inside its crystals but does not provide any evidence about whether they detect it directly or infer its presence indirectly.
 The correct answer is C.

Q6. Which of the following, if true, would most weaken the author’s conclusion in lines 18–22?
A. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
B. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
C. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
D. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
E. Viral disease is typically observed in a large proportion of the lepidoptera population.
 Evaluation 
The sentence in question presents the author’s conclusion that lepidoptera populations may be selfregulating or regulated by something more closely connected to the insects than predatory birds or parasites are. To weaken that conclusion requires weakening its support, namely, that mortality caused by predators and parasites seems not to affect population cycles, and that changing habitats and reducing populations has not altered population cycles either.A. A drop in birds and parasites preying on lepidoptera would not weaken the author’s conclusion; mortality caused by these predators has not affected population cycles.
B.  Correct . New experiments involving changes in habitat that did succeed in altering population cycles would suggest that the populations are not in fact self-regulating, and that the search for another cycle-altering agent may be unnecessary.
C. This finding would support the idea that the nuclear polyhedrosis virus is responsible for population
cycles—that is, that the virus is the closely connected agent the author concludes is responsible.
D. The suggestion that the effects of weather may not have been adequately assessed is remotely relevant to the author’s conclusion, but the mere difficulty of assessing the effects provides no positive reason to suppose that weather may be the cause of the cycles. On the other hand, answer choice B does offer evidence for an alternative explanation.
E. Viral disease is what the author ultimately suggests is the agent that drives the lepidoptera population cycles in question. The wide presence of viruses in lepidoptera could help support the author’s conclusion.
 The correct answer is B.

zoezhuyan · Answer

dear  AndrewN ,
when I reviewed this passage, I missed Q4

I picked up A, because following sentence in the paragraph 2,

would you please clarify what I missed ?

thanks in advance.

AndrewN · Answer

Hello,  zoezhuyan . You have to be careful in these detail questions to locate the correct details. Notice that the question stem refers to  nuclear polyhedrosis viruses    virulent  . The excerpt you quoted from paragraph two simply discusses how the virus is released. It appears as if you may have overlooked the line directly before the one you quoted:

We have a nearly identical match between question stem and answer choice, so (E) must be the answer. You want to simplify your approach to RC detail questions as much as possible. It is not as if the keywords will always match word for word, but most of the time, they do, and in other cases, a few words may be swapped out for synonyms.

I hope this proves helpful to you.

- Andrew

rithwiksoorya · Answer

Doesn't the "Predator" in  Option B  mean the caterpillars since they eat the crystals ?

GMATNinja · Answer

The problem with (B) is that the question stem suggests that the  virus  is attractive to predators. But that’s simply not true. At no point is the  virus  said to be attractive to predators, even if we were to argue that the crystals are attractive to caterpillars.

Also, it seems that the crystals themselves are a protein, likely embedded in the prey of caterpillars. So the crystals themselves are not the prey of caterpillars, and we can eliminate (B).

I hope that helps!

A small number of the forest species of lepidoptera (moths and butterf

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GMAT Reading Comprehension (RC) Questions

A small number of the forest species of lepidoptera (moths and butterf

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