Further research has shown that caterpillars become virtually immune to the wilt virus as the trees on which they feed respond to increasing defoliation. The trees own defenses raise the threshold of caterpillar vulnerability to the disease, allowing populations to grow denser without becoming more susceptible to infection. For these reasons, the benefits to the caterpillars of ingesting phenols appear to outweigh the costs. Given the presence of the virus, the trees defensive tactic apparently has backfired .
17. Which of the following statements best expresses the main point of the passage?
Recurring outbreaks of infestation by gypsy moth caterpillars have had a devastating impact on trees in the northeastern United States.
A mechanism used by trees to combat the threat from gypsy moth caterpillars has actually made some trees more vulnerable to that threat.
Although deadly to gypsy moth caterpillars, wilt disease has failed to significantly affect the population density of the caterpillars.
The tree species with the highest levels of phenols in their foliage are the most successful in defending themselves against gypsy moth caterpillars.
In their efforts to develop new methods for controlling gypsy moth caterpillars, researchers have focused on the effects of phenols in tree leaves on the insects growth and reproduction.
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