Biology Reference
In-Depth Information
12.
Adaptation of Plants to
Alien Herbivores and Diseases
“The ability of a population to respond to phenotypic selection depends on
the existence of genetic variation in relevant traits. Genetic variation among
host plants may make them differentially preferable to herbivores or influence
the ability of the herbivores to use them effectively.”
—B
YINGTON ET AL
. (1994)
The gypsy moth (
Lymantria dispar
) was brought to Massachusetts from
France in 1869 to investigate its potential for production of silk. Escaped
moths soon created a wild population that caused local outbreaks over a
period of years. Beginning in 1905, however, the gypsy moth began to
spread westward and southward; it now ranges west to Michigan and
south to Virginia. Gypsy moths feed on and defoliate numerous woody
plants, with oaks being highly preferred. Repeated defoliation can result
in heavy tree mortality and is thus a strong potential selective force.
Byington et al. (1994) examined the variability in growth and mortal-
ity of red oak (
Quercus rubra
) seedlings to gypsy moth defoliation. They
tested seedlings grown from acorns taken from nine parent trees, none of
which had experienced gypsy moth outbreaks. Seedlings were exposed to
moth larvae until defoliation was essentially complete. A month later, the
seedlings were analyzed. Mortality of defoliated seedlings varied from 0 to
37%. Surviving seedlings varied nearly threefold in the fraction of preex-
posure foliage that they were able to replace.They also varied in total bio-
mass and portion of biomass allocated to roots at the end of the experi-
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