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, summarize the passage in one sentence that includes (1) the initial problem/background and (2) the author’s main takeaway or study finding, especially if it appears in the final sentence. Then eliminate choices that add recommendations, exaggerate beyond the text, or contradict the reported results, and pick the option that best captures the passage’s overall point.
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
Eliminate choices that give advice the passage doesn’t give or that contradict the reported outcomes in the field trials.
Cover the whole passage, not just one detail
The best main-idea answer should include the switch to wasps and the overall results (moths, bees, and yields), not just one part.
Step-by-step Explanation
Identify the problem in the opening
The passage explains that farmers relied on an insecticide, but over time (1) the moth developed resistance and (2) nearby bee populations declined.
Identify the proposed alternative
The study proposes replacing the insecticide with a biological control: periodically releasing parasitic wasps that prey exclusively on the moth’s larvae.
Extract the key outcomes from the field trials
In field trials, the wasp strategy reduced moth numbers by 85%, allowed bee populations to rebound, and produced greater overall tomato yields than insecticide-treated plots.
Choose the option that matches the passage’s central idea
The main idea is that introducing parasitic wasps in place of the insecticide effectively controls the moth while also benefiting bees and improving tomato yields. Therefore, the best answer is: Researchers found that releasing parasitic wasps instead of using the insecticide reduces moth numbers, helps bee populations recover, and increases tomato yields.