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

avigutman can you pls clarify the role of 'if not self regulating' in '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? What does it mean exactly'? What drew the author to say it is not self regulating based on the fact that predators are not the reason? GMATNinja @jonshukruat @ronpuruwel AndrewN MartyTargetTestPrep @gmatwhizz egmat

Also not clear on Q6 wh not A? We can say that predators have been decreasing due to which they have not been able to measure the impact correctly and draw a linkage b/w predators and population cycles due to which the claim about this missing linkage is wrong. And in Q6 how do we identify that
example of habitats' is not considered as self - regulating or intimately connected when we dont really know the definition of these terms?'

dear GMATNinjaTwo, VeritasKarishma, MartyTargetTestPrep, AndrewN,VeritasPrepBrian,GMATRockstar
KarishmaB

avigutman, AndrewN,MartyTargetTestPrep ,

I am struggled with this question,
RC00120-01.
I haven't gotten where my mistakes are.
my reasoning is as following:
the author points out the evidence implies that 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.
what the evidence refers to ? obviously, the evidence is mentioned in the earlier part in P1,
in other words, predatory birds or parasites are unproductive, which leads to picked up A, A implies the birds or parasites have dropped significantly, so there are insufficient birds or parasites, so if insufficient, even the result is unproductive, it is hard to say birds or parasites are not the driving force. maybe they are the driving force, but they are so few that you cannot get the whether they are driving force or not, so we cannot rule out this potential driving forces, therefore, weaken the conclusion.

and I am also confused by C
if virus are present on birds or parasites, additional the evidence above, you can infer both virus and birds or parasites are not the driving forces.

appreciate your help.

Dear experts,
Can you please explain the correct answer choice for Question 1?
It says, "develop an explanation for the existence of lepidoptera population cycles." What confuses me here is we already know that the mentioned population cycle exists. We are trying to find out why the cycle occurs. Is it appropriate to say, "develop an explanation for the existence of lepidoptera population cycles?"
Thank you so much.

Question 1

You're right that scientists are looking for why the population cycle occurs. That's exactly what (A) is getting after: "develop an explanation for the existence of lepidoptera population cycles."

While scientists know that the population cycle exists, they still can't explain why it exists. So, they investigated parasites and predatory birds to find that explanation.

(A) is the correct answer for question 1.

I hope that helps!

Question 6

You raise good points about (A) and (C)! Before we analyze them, let's quickly reiterate the author's conclusion at the end of the first paragraph.

As you say, the author supports this conclusion by noting that studies about potential causes (such as predatory birds or parasites) have failed to explain the changes in lepidoptera populations.

Here's (A) again:

Does this cast doubt on the idea that lepidoptera are regulated by an agent other than parasites or predatory birds? The problem is, this doesn't give us very much information. So drawing that conclusion would require a number of leaps. Is it possible that the drop in the number of bird and parasite species has prevented them from regulating lepidoptera? Possibly, but that would require a pretty big assumption, so we can't safely draw that conclusion.

From another angle: even if we did make the above assumption, we don't really know when the studies were carried out. Was it before the drop? After the drop? Again, to draw any conclusions at this point would require us to make unfounded leaps.

So, since (A) doesn't give us enough information to safely draw any useful conclusions, we can eliminate it.

Let's look at (C):

Does this weaken the author's conclusion? Not really. Keep in mind that the author's conclusion in lines 18-22 is NOT that the virus is definitely regulating lepidoptera populations. Instead, the conclusion is that something "more intimately connected to the insect" is regulating lepidoptera. The fact that the virus is present "in a number of predators and parasites" doesn't weaken the idea that something aside from predators or parasites is at play.

For that reason, we can eliminate (C).

I hope that 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?

Thanks so much GMATNinja for providing these explanations, but I'm confused that why choice B does not strengthen the conclusion instead. The conclusion states that "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." It does not say that the agent is the virus. Couldn't the experiment in choice B be that agent?

Thanks so much again.

rickyric395 I read the same way!

Be careful about altering the author's language! The author isn't just saying there's "some other agent." She's saying that the population may be regulated "by an agent more intimately connected with the insect than are predatory birds or parasites." What might be "more intimately connected"? Maybe something inside the insect's cells. Like a virus!

So you're right that (B) is introducing the possibility of there being another agent, but because this agent is introduced by altering the habitat, it doesn't sound as though this other agent is more intimately connected to the insect. In other words, it's more likely that it's the altered habit that's influencing the life cycle. Not the “intimately connected” virus.

So that "intimately connected" phrase is doing some pretty heavy lifting here. Without it, you’d be right. But it’s here, and it’s important.

I hope that clears things up!

Question 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.

Explanation: The passage states that the common approach of studying the causes of population cycles in lepidoptera was to measure the mortality caused by different agents such as predatory birds or parasites. This suggests that the purpose of measuring the mortality was to develop an explanation for the existence of population cycles in lepidoptera.

Question 2: The primary purpose of the passage is to... (C) present a hypothesis about the driving force behind population cycles in lepidoptera.

Explanation: The passage primarily focuses on presenting the hypothesis that nuclear polyhedrosis viruses may be the driving force behind population cycles in lepidoptera. It discusses the research conducted, the evidence supporting the hypothesis, and the applicability of the hypothesis to different species of lepidoptera. The passage aims to present this hypothesis as a possible explanation for the regular patterns of population growth and decline observed in lepidoptera.

Question 3: According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases... (D) attacked already declining caterpillar populations.

Explanation: The passage states that before the discovery of new techniques for detecting viral DNA, population ecologists usually considered viral disease to have contributed to the decline of lepidoptera populations once it was underway, rather than to have initiated it. This implies that viral diseases were believed to attack caterpillar populations that were already in decline.

Question 4: According to the passage, nuclear polyhedrosis viruses can remain virulent in the environment only when... (E) they are sheltered from direct sunlight.

Explanation: The passage mentions that nuclear polyhedrosis viruses can remain virulent for many years in the environment if protected from direct sunlight. It states that when the viruses are embedded in durable crystals of polyhedrin protein, they can remain virulent and infect other caterpillars after the insect dies and decomposes. Therefore, the viruses' ability to remain virulent depends on being sheltered from direct sunlight.

Question 5: It can be inferred from the passage that while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus... (C) cannot infect caterpillars' cells.

Explanation: The passage mentions that once the polyhedrin protein crystals dissolve, the nuclear polyhedrosis virus is released to infect the insect's cells. This implies that while inside the crystals, the virus cannot infect caterpillars' cells.

Question 6: Which of the following, if true, would most weaken the author’s conclusion in lines 18-22? (B) New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.

Explanation: The author's conclusion in lines 18-22 is that the evidence implies that lepidoptera populations may be regulated by an agent more intimately connected with the insect than predatory birds or parasites. The passage suggests that this agent may be a virus. To weaken this conclusion, we need an option that presents an alternative explanation for the population cycles. If new experiments show that altering the habitats of lepidoptera in previously untried ways result in the shortening of population cycles, it suggests that factors other than a virus may be responsible for the cycles. Therefore, option (B) weakens the author's conclusion.

Question 5, i chose D: while inside its polyhedrin protein crystals, the nuclear polyhedrosis virus cannot be ingested by caterpillars.

It should be true that when the virus is inside the crystal, it cannot be ingested because the virus is still there even after the crystal is ingested from statement “Once ingested by a caterpillar, the crystals dissolve, releasing the virus to infect the insect’s cells”
And this statement also shows that a caterpillar ingests only the ‘crystal’ not the ‘virus’

Could anyone please explain option D why my understanding is wrong. Thank you!

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Hello GMATNinja

Really amazing explanation with so much detail. Thank you for such amazing answers which help us understand

My doubt here pertains to choice C. The author gives the highlighted conclusion at the end of the first paragraph that there might be some other agent more closely related to the insect than the predatory birds or parasites. Till this point author has not considered the possibility of the Nuclear polyhedrosis viruses so IMO while looking for points to weaken this conclusion, we need not to consider anything in particular about this virus because the same information has not been presented yet and author doesn't use this information to arrive at this conclusion, That is the reason I rejected Option C.

If there were any other option which said that the Nuclear polyhedrosis viruses don't have that much affect on the population cycle of lepidoptera, I would have rejected the same on this ground since author's conclusion is primarily concerned with some agent which is intimately connected with the insect and author till this point doesn't say that agent has to be Nuclear polyhedrosis viruses in particular. Even if an option choice said that Nuclear polyhedrosis viruses don't affect the population cycle that much there could very well be a possibility of some other agent affecting their population cycle which is intimately connected with the insect and thus such a choice won't weaken the conclusion.

So a possible weakener here should be either a statement telling us that something else not so intimately connected with the insect affects their population cycle or a statement which shows us that its impossible for any agent intimately connected with the insect to affect their population cycle.

I don't think that we should consider the information given in the subsequent passage after the conclusion has been made to weaken the conclusion.

Please tell me if my understanding is correct or not. Will wait for your reply.
Thank you

Sorry for not getting back to you sooner!

It sounds like you have the right idea in this case, but you don't want to be too rigid about disregarding stuff from later in the passage. Who knows, maybe there's SOMETHING about nuclear polyhedrosis virus that impacts the evidence described earlier in the passage. If so, that would be a valid answer, even though the author doesn't bring up the virus until later.

In short, you can eliminate (C) because it doesn't weaken the conclusion, not just because it fails on a technicality.

I hope that helps!

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