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

Dear Experts,

I have a question in Q3

RC00120-02 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

Why (A) is wrong? and


The passage mentions :
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.

I cannot eliminate (A) and (B)

From my understanding :
"population ecologists had usually considered viral disease to have contributed to the decline once it was underway rather than to have initiated it" could be implied that ecologists typically find the virus when it was underway (or in process of decline). I have no idea and feel it make no sense that virus (C) attacked already declining caterpillar populations.

Could any experts help me eliminate (A) and (C), and explain why (C) is correct?

Thank you in advance

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.

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 lepidopteras

(C) were the driving force behind Lepidoptera population cycles

(D) attacked already declining caterpillar populations

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.

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.

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!

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!

Hey GMATNinja , Author is concluding that there is some other agent that is affecting insect's population more than birds and parasite. So a possible weakener would be to show that birds and parasites are indeed on same or greater level than this other agent. Please let me know if I am right? If I am, then wouldn't option B weaken the idea behind this weakener thereby strengthening it?

Hey [url=https://gmatclub.com:443/forum/memberlist.php?mode=viewprofile&un=GMATNinja%5D%5Bb%5DGMATNinja%5B/b%5D%5B/url%5D , Author is concluding that there is some other agent that is affecting insect's population more than birds and parasite. So a possible weakener would be to show that birds and parasites are indeed on same or greater level than this other agent. Please let me know if I am right? If I am, then wouldn't option B weaken the idea behind this weakener thereby strengthening it?

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!