By competing with rodents for seeds, black ants help control

To be precise, the author's conclusion is that the planned introduction of ant flies into that region would benefit public health. And here's how the author gets there logically:

• Black ants compete with rodents for seeds.
• That competition helps control rodent populations that pose a public health risk.
• The Loma ant, which has recently invaded a certain region, has a sting that's fatal to humans.
• There is a plan to introduce ant flies to that region. These ant flies prey on Loma ants.
• Therefore, the planned introduction of ant flies into that region would benefit public health.

If the conclusion we're trying to strengthen states that introducing ant flies would benefit public health, we need to think about what would help or harm public health.

• HELP: We know that the Loma ant can be fatal to humans. So it would be great to see a choice further showing that ant flies will reduce the number of Loma ants in this region.
• HARM: We know that black ants benefit public health by controlling the rodent populations that are posing a public health risk. So it would be bad to see a choice showing that ant flies also reduce the number of non-Loma ants in this region. If that happens, then we'd be less certain about the public health benefits, because the risk from rodents could go up just as the risk from Loma ants goes down.

From the information in this passage, we know that the ant flies prey on Loma ants. This does NOT tell us that the ant flies ONLY prey on Loma ants. Maybe that's the case. Maybe ant flies prey on many other kinds of ants as well. We can't tell based on what we've read.

Choice (A) recognizes this lack of information and fills this gap perfectly. Knowing for sure that ant flies do not attack black ants other than Loma ants rules out potential harm to humans from a reduction of non-Loma ants.

That's why we keep (A).

Now, let's take a second look at choice (C):


You've written that "Option C states that if LA are wiped out by ant flies, the Rodent population would still be under control." But this choice never mentions ant flies, and doesn't give us any kind of information to support a reduction in public health risk.

Choice (C) does give us more reason to believe that non-Loma ants can better control the rodent population. So what? This doesn't have any impact on our confidence in the plan to introduce ant flies:

• Knowing this information doesn't reduce the likelihood that Loma ants will sting and kill human beings.
• Knowing this information actually makes it seem less likely that this region will have its rodent population controlled, because we now know that Loma ants are aggressively invading this region, and they're definitely worse at rodent population control than non-Loma. If anything, we should expect rodent population control to get worse due to the increase in less efficient Loma ants, therefore increasing public health risk overall.

Choice (C) doesn't offer any logical support of the conclusion that we're trying to strengthen, so we must eliminate it.

I hope this helps!

Answer A cus only loma ants cause harm to people and not the other kind of black ants.

B C D are wrong.
While A and E both strengthen, the conclusion is inferred from the premise that the planned introduction of ant flies benefits public health. Thus, a premise where ant flies is an advantage should be the correct answer. Eliminate E and answer is A.

Hi,

it is indeed given in the conclusion that the introduction of ant flies will benefit
but in a strengthener we don't take the conclusion at its face value we need to prove it!! the conclusion is not taken for granted we only take the premises and the underlying assumption(logic connecting the premise to the conclusion) for granted

the reasoning or the underlying assumption will answer this question-why is the author saying that ant flies are beneficial?
in what ways can the ant flies not be beneficial?
1) what if they killed both the loma ants and the other ant species
2)what if ant flies kill loma ants but they themselves do something else that causes a threat to the public health, maybe they release some poison after killing loma ants thats even more fatal too humans.(just taking some wild guesses but which are relevant to the passage)

we must make sure that we strengthen only the reasoning and prove that the conclusion is in fact possible or it is true!!

in option E - if the argument is trying to find a solution to improving public health by killing loma ants

introducing another factor such as pesticides makes no sense as pesticides harm the environment and it can be worse than loma ants so when we can kill loma ants using ant flies why would we further damage the environment by bringing in pesticides..

usually in CR prompts we should stick to the scope of the argument i.e. the argument is only concerned with attacking loma ants using ant flies
therefore using any other chemical/pesticide/trap anything way of killing loma ants is out of scope to the argument!

I hope this helps

Solution

Passage Analysis

• By competing with rodents for seeds, black ants help control rodent populations that pose a public health risk.
o Rodents are a public health risk.
o Black ants compete with rodents for seeds.
o This mechanism helps control rodent population.
• However, a very aggressive species of black ant, the Loma ant, which has recently invaded a certain region,
o But, there is a very aggressive species of black ants called the Loma ant.
o Loma Ants have recently invaded a particular area.
• has a venomous sting that is often fatal to humans.
o These Loma Ants have a poisonous sting that can kill humans.
• Therefore, the planned introduction into that region of ant flies, which prey on Loma ants, would benefit public health.
o Ant flies prey on Loma ants.
o It is planned to introduce ant flies into the area invaded by Loma ants.
o It is concluded that this action will benefit public health.

Question Stem Analysis

Which of the following, if true, most strengthens the argument?
This is a straightforward strengthener question.

Prethinking

The conclusion we need to strengthen is that the planned introduction of ant flies into the region will benefit public health. This can be done in various ways.
Strengthener 1- Ant flies do not attack other black ants except Loma ants.
Strengthener 2- Ant flies do not attack humans / are not detrimental to humans in any way.

Answer Choice Analysis

(A) Ant flies do not attack black ants other than Loma ants.
CORRECT
This is the right answer as it is in line with our prethought strengthener 2. If this statement is true, other black ants that compete with rodents are safe, thus checking the rodent population and thereby controlling the public health risk caused by rodents.

(B) Loma ants are less effective than many bird species in competing with rodents for seeds.
INCORRECT
This option does not address the introduction of ant flies. Hence it is not a relevant answer choice.

(C) Certain other species of black ants are more effective than Loma ants in competing with rodents for seeds.
INCORRECT
This option does not address the introduction of ant flies. Hence it is not a relevant answer choice.

(D) The sting of Loma ants can also be fatal to rodents.
INCORRECT
We are not concerned about how Loma ants can control rodent populations. Irrespective of whether their sting is fatal to rodents, the issue is that is fatal to humans. This option effectively weakens the conclusion by trying to indicate that the entry of ant flies would remove Loma ants, which are effective in controlling rodents.

(E) The use of pesticides to control Loma ants could have harmful effects on the environment.
INCORRECT
We are not concerned about the harmful effects on the environment in this scenario. We are only concerned about public health. It should be explicitly mentioned if both are connected. It also does not speak about ant flies. Hence this option is also out of scope.

From the passage we know that the Loma ant has invaded a certain region, but you can't assume that Loma ants are the ONLY ants in that region. There could still be any number of other black ant species in that area. (A) tells us that any of these other ants in the region won't be killed off by the ant flies. So, these other species can continue to control the rodent population, which is good for public health.

As for (D), consider this chain of logic:

• Rodents pose a public health risk
• Black ants help to control the rodent population by competing for the same food -- so, black ants are good for public health!
• Sadly, one of these species of ant, the Loma, can kill people -- so Loma ants are bad for public health.
• Ant flies eat Loma ants
• Therefore, the author thinks that introducing ant flies will improve public health because the Loma ants will be killed off.

We're trying to strengthen the author's argument. How does (D) stack up?

The author wants to kill off the Loma ants to improve public health. (D) tells us that Loma ants are actually doing something nice for humans -- they fatally sting rodents. If this were true, then the bad thing that Loma ants do (fatally stinging humans) might be offset by the good thing that they do (killing off rodents). If anything, (D) muddies the water by implying that Loma ants aren't 100% bad for public health. So, (D) somewhat weakens the author's argument that killing the Loma ants will benefit public health.

Eliminate (D).

I hope that helps!

Hello GMATNinja GMATNinjaTwo

Need help regarding this question.

In this question, conclusion is that it would be beneficial for public health if ant flies are introduced and they kill the Loma ants.

How is it assumed from the premise, that ant flies may attack other ant species also when the conclusion explicitly states only Loma ants ? OA depends on this assumption.

If the premise clearly states that LA is the one that will be affected why do we need to see other ant species

Option C states that if LA are wiped out by ant flies, the Rodent population would still be under control since the other ants would still keep the rodents under control. If I consider it true that only LA are affected by rodent, I would get this answer.

In the second statement, does the phrase "has recently invaded a certain region" mean that there are no other species of black ants in that region?
I actually presumed that only L ants are present in the region (because they are aggressive and have invaded the region).

Also, I choose D because if the sting of L ants can also be fatal to rodents then the rodent population would be under control and therefore, benefit PH. And, the last part of 2nd sentence does not say that the sting is only harmful to human.


Experts please help.

Thanks

I was confused between A/C. Please correct my analysis.

A -> Ant Flies don't attack other ants, Isn't this info redundant. In the argument, this is already stated right(They prey on Lona ants).

C -> If Lona ants are the ones, which are effective against the control of rodent population. Then by killing then could be harmful to the environment.

So, If Lona ant's contribution in controlling the rodent population is the least, Killing of them will not have any impact. Hence I picked C

Check out this post and see if that clears things up!

A good reason to eliminate both B and C:
(C) Certain other species of black ants are more effective than Loma ants in competing with rodents for seeds.
2 cases are possible:
1) Both Loma and non-loma are good in competing - If Loma is good in general (absolute) but less effective compared to non-loma in competing with rodents for seeds. It helps to control rodent population, therefore decreases public health risk. So we should not kill Loma. It weakens the plan to kill Loma by introducing ant flies
2) If Loma is bad in general (absolute) and less effective compared to non-loma (also bad) in competing with rodents. Both increase in rodent population and threat by Loma ants increases public health risk overall. So we should kill Loma. It strengthens the plan to kill Loma by introducing ant flies
We don't have enough information to conclude which case is possible.
Comparison doesn't tell us anything about how good or bad they are competing with rodents for seeds.

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