Question 146·Medium·Central Ideas and Details
Until recently, farmers in a coastal region relied on a potent insecticide to protect their tomato fields from a destructive moth. Over time, however, the moth developed resistance to the chemical, and nearby populations of pollinating bees declined. A new study proposes an alternative: periodically releasing parasitic wasps that prey exclusively on the moth’s larvae. In field trials, this biological control strategy reduced moth numbers by 85 percent, allowed bee populations to rebound, and led to greater overall tomato yields than plots treated with the insecticide.
Which choice best states the main idea of the text?
For main-idea questions, first summarize the passage in your own words in one short sentence, focusing on the relationship between the problem and the solution or the study’s overall finding. Then eliminate choices that (1) focus only on background details, (2) add extreme or unsupported claims, or (3) contradict any part of the passage. Finally, choose the option that reflects the entire passage—especially the results or conclusions in the final sentences—rather than just the setup at the beginning.
Hints
Look for problem and solution
Identify what problem the farmers are facing and what new approach the study suggests. Main-idea questions often hinge on how the solution addresses the original problem.
Pay attention to the results
Focus on the field trials: what happened to moth numbers, bee populations, and tomato yields when the new method was used? Any correct answer should reflect these outcomes.
Beware of extreme or unsupported claims
Check each option for words like "completely," "solely," or claims about harm that are not stated in the passage. Eliminate choices that contradict or go beyond the text.
Cover the whole passage, not just one sentence
Make sure the choice you select doesn’t just describe the problem or just the background; it should capture both the old method’s issues and what the study found about the new method.
Step-by-step Explanation
Identify the situation and problem
Read the first two sentences:
- Farmers relied on a potent insecticide to protect tomatoes from a destructive moth.
- Over time, the moth developed resistance to the chemical.
- Nearby bee populations declined.
So the problem is that the old chemical method both became less effective against the moth and harmed pollinating bees.
Understand the proposed solution
Look at the next sentence:
- A new study proposes an alternative: periodically releasing parasitic wasps that prey exclusively on the moth’s larvae.
This introduces a new pest control strategy (biological control using parasitic wasps) to replace the insecticide.
Note the results of the new strategy
Focus on the last sentence about the field trials:
- The biological control strategy reduced moth numbers by 85 percent.
- It allowed bee populations to rebound.
- It led to greater overall tomato yields than plots treated with the insecticide.
The passage is emphasizing that this new method is more effective overall and is better for bees and crop yields than the insecticide.
State the main idea and match it to the answer choice
The central idea is that researchers tested a new biological control method—releasing parasitic wasps—in place of the insecticide, and found that it both controls the moth and benefits bees, resulting in higher tomato yields than insecticide use.
Among the choices, only D clearly and accurately describes this full main point, so the best answer is: D) Researchers found that introducing parasitic wasps instead of using the insecticide both suppresses the moth and benefits bees, ultimately increasing tomato yields.