More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests. However, biocontrol agents can negatively affect nontarget species by, for example, competing with them for resources: a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs.Another example of indirect negative consequences occurred in England when a virus introduced to control rabbits reduced the amount of open ground (because large rabbit populations reduce the ground cover), in turn reducing underground ant nests and triggering the extinction of a blue butterfly that had depended on the nests to shelter its offspring. The paucity of known extinctions or disruptions resulting from indirect interactions may reflect not the infrequency of such mishaps but rather the failure to look for or to detect them: most organisms likely to be adversely affected by indirect interactions are of little or no known commercial value and the events linking a biocontrol agent with an adverse effect are often unclear. Moreover, determining the potential risks of biocontrol agents before they are used is difficult, especially when a nonnative agent is introduced, because, unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways so that it can feed on or otherwise harm new hosts.



According to the passage, which of the following is a concern that arises with biocontrol agents but not with chemical pesticides?

(A) Biocontrol agents are likely to destroy desirable species as well as undesirable ones.
(B) Biocontrol agents are likely to have indirect as well as direct adverse effects on nontarget species.
(C) Biocontrol agents may change in unforeseen ways and thus be able to damage new hosts.
(D) Biocontrol agents may be ineffective in destroying targeted species.
(E) Biocontrol agents may be effective for only a short period of time.

I originally got A for this one, but the answer is C. Can some one please explain to me why A is wrong? I read some of the posts, people are saying because the first sentence indicates A is wrong, it means for most chemical pesticides, not biocontrol agents. Can anyone explain to me if that is right? When the sentence construct as:
More selective than most chemical pesticides in that they ordinarily destroy only unwanted species, biocontrol agents (such as insects, fungi, and viruses) eat, infect, or parasitize targeted plant or animal pests.
What they refers to in this particular sentence, is it refers to pesticides or agents? I thought C is right because the sentence:
a biocontrol agent might reduce the benefits conferred by a desirable animal species by consuming a plant on which the animal prefers to lay its eggs.

Can someone please also explain to me what does it mean "reduce the benefits conferred by a desirable animal species"

Thank you!

what is the source of this question?


this question is explictly answered in the last sentence of the passage: unlike a chemical pesticide, a biocontrol agent may adapt in unpredictable ways so that it can feed on or otherwise harm new hosts.

bolopaneer, thanks.



this means that some other animal species has positive effects (benefits) in some situation; “reduce the benefits” signifies that the use of biocontrol agents will work against those positive effects.

This is another question from GMAT Prep (test 2) related to the same passage.

The passage is primarily concerned with

(A) explaining why until recently scientists failed to recognize the risks presented by biocontrol agents
(B) emphasizing that biocontrol agents and chemical pesticides have more similarities than differences
(C) suggesting that only certain biocontrol agents should be used to control plant or animal pests
(D) arguing that biocontrol agents involve risks, some of which may not be readily discerned
(E) suggesting that mishaps involving biocontrol agents are relatively commonplace

Official answer: [D]

Can somebody explain why the correct answer is better than choice A and what's wrong with A?

well, the correct answer is better because A is wrong. :) why is A wrong? this is the type of question you should anticipate before it shows up, so you should already have an idea in mind of what the passage is about. without looking at the answer choices, you should recognize that this passage is about SOMETHING having to do with biocontrol agents. in particular, the passage is about the risks posed by biocontrol agents. the problem with A is it incorrectly puts the focus on the scientists and whether they recognized the risks. this is only a small part of the passage, and certainly not the primary focus..

_________________
Tim Sanders
Manhattan GMAT Instructor