(65) are quickly suppressed by viral
epidemics.
Further research has shown that cater-
pillars become virtually immune to the
wilt virus as the trees on which they
(70) 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
(75) more susceptible to infection. For
these reasons, the benefits to the
caterpillars of ingesting phenols
appear to outweigh die costs. Given
the presence of the virus, the trees
(80) defensive tactic apparently has
backfired.
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 cater-
pillars, 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