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Difficulty: MediumWeakening Arguments

To curb economic losses from bark beetle infestations, timber managers introduced a predatory beetle species that preys exclusively on adult bark beetles during their early spring mating period. Researchers concluded that this biological control measure will significantly increase timber yields over the coming decade. They reason that suppressing adult bark beetle numbers during early spring will prevent the beetles from boring into mature trees and depositing larvae, which cause extensive structural damage to wood tissue. Which of the following, if true, most seriously weakens the researchers' argument?

  1. The vast majority of timber destruction attributed to bark beetles is caused by larvae that hatch from eggs deposited by adult beetles in late autumn, prior to the spring mating period.Answer
  2. B
    Laboratory experiments demonstrate that the introduced predatory beetles consume adult bark beetles at a significantly higher rate when spring ambient temperatures rise.
  3. C
    Chemical pesticides previously used against bark beetles caused temporary foliage discoloration in several non-target tree species.
  4. D
    Logging companies in neighboring timber regions have recently adopted mechanized harvesting equipment that reduces processing times.
  5. E
    In regions where predatory beetle populations increased naturally, timber yields rose during years that also experienced unusually mild winter temperatures.

Answer

The argument is most seriously weakened by the finding that the vast majority of timber destruction is caused by larvae hatching from eggs deposited in late autumn, prior to the spring mating period.
The correct answer weakens the argument by demonstrating a critical timing mismatch in the causal chain. The researchers claim that suppressing adult bark beetles during the spring mating period will prevent destructive larvae from damaging timber. However, if the larvae responsible for the vast majority of wood destruction hatch from eggs deposited during the preceding autumn, suppressing spring adults will do nothing to stop the damage caused by larvae already present in the trees.

Step-by-Step Solution

1
Identify the conclusion and underlying causal chain
The researchers conclude that introducing predatory beetles in early spring will increase timber yields because suppressing spring adult beetles will prevent them from laying destructive larvae.
Evaluating a weakening question requires isolating the precise link between the premise (spring predation of adults) and the conclusion (reduced wood damage and increased yield).
2
Identify the critical vulnerability in the reasoning
The argument assumes that spring is the period during which the damaging larvae are produced.
If larvae causing the destruction are produced at a different time, controlling adults in spring will fail to prevent timber damage.
3
Evaluate option impacts against the vulnerability
The statement specifying that destructive larvae hatch from eggs laid in late autumn breaks the connection between spring adult predation and damage prevention.
Because the eggs leading to larval damage were already deposited months earlier, spring intervention comes too late to protect the timber.

Key Concept

Weakening Causal Arguments by Breaking Premise-Conclusion Assumptions
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Topics

Weakening Arguments

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