Synthetic pyrethroids are pesticides recommended for use in apple orchards to control leaf miners, insects whose larvae feed on the leaves of apple trees. Synthetic pyrethroids also kill predators of spider mites, however. Thus these pesticides do more overall harm than good in an apple orchard.

Which of the following, if true, most strengthens the argument above?

Premise: Larvae of LM insects feed on leaves of apple trees and pesticide SP helps control the the LM. SP also kill predators of spider mites.
Conclusion: SP does more harm than good to apple orchard.

So, there's a contrasting finding that one SP does one good thing by controlling/killing LM insects. But when it helps kill predators of spider mites all good done turns into harm. Clearly, predators of SM must be doing something good for the apple orchard. If that's the case, then SM might be doing harm to Apple orchard.

A. Spider mites are beneficial to apple trees. - WRONG. Goes in opposite direction. Weakens the argument.
B. Predators in apple orchards do more harm than good. - WRONG. Again its in the opposite direction.
C. Many consumers avoid buying apples that have been treated with pesticides. - WRONG. Looks promising so we can keep it, initially, till we find a better one.
D. Spider mites are potentially more serious pests in apple orchards than are leaf miners. - CORRECT. If SM are more dangerous than LM then predators of SM helped control the SM. Killing the predators would be least which someone would demand. So, killing predators did more harm than good. Note the comparison of 'more seriously', although 'harm' done by SM is obvious as it is compared with LM which harm apple orchard.
E. Leaf miners are sometimes parasitized by other insects. - WRONG. 'Sometimes' is problematic here.

Note: This problem has two steps that must be noted.
1. SP does one good thing by killing LM.
2. Other one of SP is bad for apple orchard when it kills SM's predators. Here again two things are layered in the passage. We don't know, initially, whether SM or its predators do good or bad(although we know it would most likely be SM) for Apple orchard which is what we need to find along with the relationship of SM and LM.

IMO. Answer D.
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IMO A cus the argument says "synthetic pyrethroids also kill predators of spider mites, however" meaning its a bad thing that SP kills spider mites.
The argument further goes on to say "thus these pesticides do more overall harm than good in an apple orchard" hence we need an answer choice that explains why its a "bad" thing that SP kills spider mites. A does so.

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Its D. The same logic goes to support D and not A. A is the opposite. (i didnt read carefully)

This passage is very confusing. What the author means that spider mites are potentially more harmful pests than the leaf miners. Hence if predators or spider mites are killed, population of spider mites will increase, causing more harm than good.



A. Spider mites are beneficial to apple trees. Here, if the spider mites are beneficial to the apple trees. Then, ideally after their predators are dead their population will increase which will be a good thing as spider mites are beneficial for the orchids. Hence pesticides are doing a good job. The conclusion is that pesticides are doing a bad job. Hence this will weaken the argument. We want to say that the pesticides are doing harm. But option A suggests that they are doing good.

B. Predators in apple orchards do more harm than good. For the above reason it strengthens the argument. Predators of spider mites are good guys (according to the passage). They are protecting the orchids from spider mites. If the pesticides are killing predators ( i.e the good guys), that makes pesticide the bad guys. This is what the argument suggests. Option B says the predators are bad guys.And pesticides are doing a good job by killing them. Hence option B is weakening the argument (Arguments wants the pesticides to be the bad guys)

C. Many consumers avoid buying apples that have been treated with pesticides. Irrelevant, hence eliminated.

D. Spider mites are potentially more serious pests in apple orchards than are leaf miners. This supports the argument. We want the spider mites to be dead, Hence the predators of spiders (the good guys should be alive. The pesticides are killing them. Hence pesticides are doing more harm than good. It is strengthening the argument.

E. Leaf miners are sometimes parasitized by other insects. Irrelevant.