Dutch elm disease, which is caused by the fungus C. ulmi spread by adu

Question

Dutch elm disease, which is caused by the fungus  C. ulmi  spread by adult scolytid beetles, has already destroyed 70 percent of the elms in Greenwood Forest. Another naturally occurring fungus,  P. oblonga , kills larvae of the scolytid beetle. Forest rangers plan to introduce  P. oblonga  into Greenwood Forest in order to save the remaining mature elms.

Which of the following, if true, would cast the most serious doubt on the plan's prospects for success?

(A) During the last year, the scolytid beetle population in Greenwood Forest has decreased by 30 percent because of cold-weather conditions.

(B) Dutch elm disease cannot be abated by introducing chemical compounds used to arrest the diseases of many other species of tree.

(C) Introduction of  P. oblonga  saved elm trees in neighboring Gatemar and Lavemont forests.

(D) For  P. oblonga  to control scolytid beetles successfully, it must be established in a forest prior to the beetle infestation.

(E) Greenwood Forest has lost many maple trees because of a fungus infection.

This question is different from  the other question  with same prompt.

GMATNinja · Accepted Answer

Ok, let's take a look at the passage before narrowing down the answer choices. The passage tells us:
  Dutch elm disease has already killed 70% of the elms in Greenwood Forest 
 This disease is caused by the  C. ulmi  fungus 
 This fungus is spread by adult scolytid beetles 
 The larvae of these beetles can be killed by another fungus,  P. oblonga  
 Park rangers plan to introduce  P. oblonga  into the forest to control the scolytid beetle population and save the remaining elms

In summary, the rangers plan to reduce the beetle population by using a "good" fungus. One knock-on effect of this plan is that the beetles will not be able to spread the "bad" fungus to the elm trees and give them Dutch elm disease.

We're asked to find the answer choice that would cast the most doubt on the plan's chances of success. Let's take a look at the options:
 
If the beetle population has decreased by 30 percent, there are fewer beetles to spread the  C. ulmi  fungus and fewer adult beetles to produce larvae. This means the  P. oblonga  fungus could be concentrated on a smaller number of larvae, potentially making the plan more effective.

(A) does not cast doubt on the plan's chances of success -- (A) is out.

(B) tells us there are chemicals that have been used to stop the diseases of many other tree species but these won't work on Dutch elm disease.

Knowing another solution does not work does not tell us anything about whether the rangers' plan will work. This doesn't cast doubt on the plan's chances of success, so (B) cannot be our answer.

Knowing that the introduction of the  P. oblonga  fungus saved elm trees in neighboring forests doesn't cast doubt on the plan's chances of success. If anything, it gives us greater confidence in the plan -- (C) is out.

We know the forest is already infested with beetles, that's how the elm trees are getting Dutch elm disease. If  P. oblonga  must be introduced into a forest before the beetle infestation, the rangers are too late and their plan is unlikely to succeed.

(D) looks good but let's take a look at (E).

We're interested in the rangers' plan to save the  elm trees  from Dutch elm disease caused by a specific fungus. The fact that Greenwood forest has lost many  maple trees  doesn't help us determine the chances of success of the rangers' plan -- (E) is out.

The only answer we haven't crossed out is (D) -- (D) is our answer to this question.

I hope that helps!

subhaalifa · Answer

Dutch elm disease, which is caused by the fungus C. ulmi spread by adult scolytid beetles, has already destroyed 70 percent of the elms in Greenwood Forest. Another naturally occurring fungus, P. oblonga, kills larvae of the scolytid beetle. Forest rangers plan to introduce P. oblonga into Greenwood Forest in order to save the remaining mature elms.

Which of the following, if true, would cast the most serious doubt on the plan's prospects for success?

(A) During the last year, the scolytid beetle population in Greenwood Forest has decreased by 30 percent because of cold-weather conditions.

(B) Dutch elm disease cannot be abated by introducing chemical compounds used to arrest the diseases of many other species of tree.

(C) Introduction of P. oblonga saved elm trees in neighboring Gatemar and Lavemont forests.

(D) For P. oblonga to control scolytid beetles successfully, it must be established in a forest prior to the beetle infestation.

(E) Greenwood Forest has lost many maple trees because of a fungus infection.

i didnt understand the reason. I have answered A

imyuva · Answer

My answer is D.

D says that P.oblonga must be introduced before beetle infestation. So as per plan if P.Oblonga introduced now, there would be no effect. Plan won't save remaining trees.

Sent from my KIW-L22 using  GMAT Club Forum mobile app

RiseAndShinee · Answer

Please help in narrowing down to OA.

jaisonsunny77 · Answer

Type: Weaken the objective

Objective: introduce P. oblonga  into Greenwood Forest in order  to save the remaining mature elms. 
  
(A) During the last year, the scolytid beetle population in Greenwood Forest has decreased by 30 percent because of cold-weather conditions.  -  Does not weaken the objective.  
 
(B) Dutch elm disease cannot be abated by introducing chemical compounds used to arrest the diseases of many other species of tree.  -  does not weaken the objective. 
 
(C) Introduction of P. oblonga saved elm trees in neighboring Gatemar and Lavemont forests.  -  what happened in other forests may not be true for the particular forest under consideration.

(D) For P. oblonga to control scolytid beetles successfully, it must be established in a forest prior to the beetle infestation. - (D) implies that introducing the beetles after the infestation has already occurred will not necessarily save the remaining mature elm trees. Hence, the desired objective may not occur. Therefore,  (D) is the right answer choice .

(E) Greenwood Forest has lost many maple trees because of a fungus infection.  -  does not weaken the likelihood of the objective.

sahilhafnia · Answer

A disease is caused in elms by some fungus Ulmi, which itself is spread by some beetles. One solution has been proposed now : introduce naturally-occurring fungus Oblonga because it can kill the larvae of those beetles. This means no more beetles and so no more spread of Ulmi. So no more elms die. 
A fairly straight and direct plan it seems.

Now how do we weaken the plan ? 
I could think of this : what if Oblonga kills beetle larvae but also eggs of elms or babies of elms directly. Will the elms be safe then... i dont think so . 
 Similarly , Oblonga kills beetle larvae but what if it supports revival of some other deadly fungus against the elms. Even in that case, elms wont be safe.

Looking at options :

1) So last year 30 % beetles died because of cold weather. But does it anywhere tell us that beetles have died completely, or will die completely in the future or that 30% decline was enough for the fungus Ulmi to stop spreading. It doesn't and hence it is incorrect option.

2) This option states that chemical method of killing beetles doesn't exist or is not at all useful. It seems this option actually gives us a reason to think and favor more about using a biological method, as given in the passage of using fungus Oblonga. Sort of supports the plan and not weaken it. Incorrect choice.

3) So, the elm trees were saved in neighbouring forests. This actually gives us more confidence about using Oblonga and helps us incline more towards the plan as given in the passage. Doesn't weaken it , so incorrect option.

4) This option states a condition for the success of the plan. It states that the fungus Oblonga is successful in killing beetles and hence protect elm trees only when it was introduced before the beetle came in the forest. But as far as we know, the beetle is already there and we are planning to introduce Oblonga later and not before. So , it seems likely that the plan can fail . This seems to weaken the plan and can be our correct choice.

5) Our forest has lost many maple trees due to fungus. But is that our area of focus. Why are we even talking about maple trees when our plan itself focuses on elm trees. No where exists a link between maple and elm trees and fungus. This option has no impact on our plan . Incorrect choice.

Correct answer should be D.

bronaugust · Answer

To solve this question, you may follow the    IMS's four-step technique   .

STEP #1:  FIGURE OUT THE QUESTION TYPE BY READING THE QUESTION STEM

The question stem states, 'Which of the following, if true, would cast the most serious doubt on the plan's prospects for success?' Clearly, we are dealing with a weakening question. Now that we know we need to weaken the argument, let us proceed to the second step.

STEP #2:  DECONSTRUCT THE ARGUMENT

In a weakening question, it is a must to deconstruct the argument by figuring out the conclusion and the premise. The plan itself is the conclusion and the basis on which the plan is formulated becomes the premise.

CONCLUSION:   Forest rangers plan to introduce  P. oblonga  into Greenwood Forest in order to save the remaining mature elms.

PREMISE:   A naturally occurring fungus,  P. oblonga , kills larvae of the scolytid beetle, which spreads fungus  C. ulmi , and this fungus causes Dutch Elm disease, which has already destroyed 70 percent of the elms in Greenwood Forest.

Now that the argument is deconstructed, let us proceed to the third step.

STEP #3:  FRAME A SHADOW ANSWER/KNOW WHAT THE RIGHT ANSWER SHOULD BE DOING

Remember, we are dealing with a plan. A planning argument goes with the assumption that the plan will work. Therefore, any answer option that gives you a situation indicating the plan will not work or one that introduces a situation stating there will be problems with the plan becomes the right answer. Now that we know what the right answer needs to be doing, we may proceed to the final step.

STEP #4:  ELIMINATE THE INCORRECT ANSWER OPTIONS

Answer options that are beyond the scope of the argument besides the ones that strengthen it can be eliminated.

(A) During the last year, the scolytid beetle population in Greenwood Forest has decreased by 30 percent because of cold-weather conditions. -   OUT OF SCOPE   - What has happened to the scolytid beetle population in Greenwood Forest is irrelevant, for the plan deals with introducing  P. oblonga  in the forest. -   ELIMINATE

(B) Dutch elm disease cannot be abated by introducing chemical compounds used to arrest the diseases of many other species of tree. -   OUT OF SCOPE   - The argument does not deal with chemical compounds, so this option is beyond the scope of the argument. -   ELIMINATE

(C) Introduction of  P. oblonga  saved elm trees in neighboring Gatemar and Lavemont forests. -   STRENGTHENS   - We are looking for an answer option that indicates that the plan may not work; however, this gives more of a reason to the forest rangers to go ahead with the plan. -   ELIMINATE

(D) For  P. oblonga  to control scolytid beetles successfully, it must be established in a forest prior to the beetle infestation. -   WEAKENS   -  This answer option indicates that if P. oblonga is introduced now, it will not be able to control scolytid beetles successfully. The beetle infestation has already occured, and this is clear from the fact that 70 percent of the elms in Greenwood Forest is already destroyed.  -   KEEP

(E) Greenwood Forest has lost many maple trees because of a fungus infection. -   OUT OF SCOPE   - Not worried about what has happened to maple trees. -   ELIMINATE

Hence, D is the right answer.

QQum · Answer

Hello Subhaalifa,

A only supports the finding put forth by the paragraph and does not really establish a relationship between the solution suggested and the problem in front of us.

Whereas on the other hand, Option D suggested that the solution may not prove useful as the pre-condition for it to work involves that P. oblonga should be introduced before beetle infestation; hence, it's a precautionary measure only successful before the problem has propped up.

VerbalBot · Answer

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Dutch elm disease, which is caused by the fungus C. ulmi spread by adu

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