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Difficulty: HardCompleting the Passage Logically

Agricultural researchers recently developed a genetically modified strain of wheat designed to emit a synthetic distress pheromone whenever attacked by aphids, thereby attracting native parasitic wasps that prey on the aphids. In initial trials, aphid infestation levels fell by 75 percent without requiring synthetic insecticides. However, subsequent ecological monitoring revealed that because the wheat continuously synthesizes the pheromone throughout its entire growth cycle—even when aphid density is negligible—local parasitic wasp populations suffer severe energy depletion from futile search behaviors, leading to a complete population collapse by the third harvest. Therefore, to sustain the efficacy of this biological pest management strategy across multiple growing seasons, farm managers should __________.

Which of the following choices most logically completes the passage?

  1. A
    apply broad-spectrum chemical insecticides during periods of low aphid density to eliminate any remaining pests before wasp populations decline
  2. B
    increase the planting density of the bio-engineered wheat per acre to maximize the total concentration of emitted distress pheromones
  3. alternate the bio-engineered wheat with non-pheromone-emitting crop varieties to ensure periods during which parasitic wasps are not exposed to constant, unrewarded foraging cuesAnswer
  4. D
    introduce additional predatory insect species into the fields to supplement the pest-control role of the parasitic wasps
  5. E
    conclude that biological pest management strategies are fundamentally incapable of replacing synthetic chemical treatments in commercial agriculture

Answer

To sustain the efficacy of this biological pest management strategy across multiple growing seasons, farm managers should alternate the bio-engineered wheat with non-pheromone-emitting crop varieties to ensure periods during which parasitic wasps are not exposed to constant, unrewarded foraging cues.
The correct response logically completes the passage by directly counteracting the biological mechanism causing wasp population collapse. The passage states that wasps suffer energy depletion because the wheat continuously emits distress pheromones even when aphids are scarce. Alternating the bio-engineered wheat with non-emitting crops breaks this continuous false signal, giving wasp populations periods without futile foraging cues so they can survive across consecutive seasons.

Step-by-Step Solution

1
Identify the primary goal and core problem presented in the stimulus
Goal: Sustain the efficacy of the bio-engineered wheat pest management system over multiple seasons. Problem: Continuous pheromone emissions exhaust wasp energy during periods of low aphid density, causing wasp population collapse by season three.
Completing the argument requires finding a measure that directly eliminates the root cause of the wasp population collapse without undermining the biological pest control objective.
2
Analyze the cause-and-effect relationship established by the premises
Continuous emission during low aphid periods → Futile wasp foraging → Energy depletion → Wasp population crash.
To prevent the wasp population crash, the continuous false signaling during periods without aphids must be interrupted or mitigated.
3
Evaluate the option choices against the required logical completion
Alternating with non-emitting crop varieties provides resting periods where wasps are not subjected to unrewarded foraging cues, directly addressing the mechanism of energy depletion.
Only an option that resolves the unrewarded foraging mechanism while maintaining the biological control strategy logically completes the manager's action statement.

Key Concept

Logical Completion through Cause-and-Effect Synthesis
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Topics

Completing the Passage Logically

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