Biology Reference
In-Depth Information
17.
Evolutionary Ecology of Alien
Biological Control Agents
“Another pervasive problem engendered by the fact that biological-control
agents are alive is that they evolve.”
—S
IMBERLOFF AND
S
TILING
(1996)
Common St. John's wort (
Hypericum perforatum
) is a European broad-
leaved herb that was introduced into eastern North America in the late
1700s. It ultimately reached the western United States and Canada,
where, because of its toxicity to livestock, it became a noxious weed over
millions of hectares. It also became a noxious weed in Australia, where
one of the earliest successful biological control campaigns was carried out
on it, using three foliage-feeding beetles. Prior to their release, Australian
scientists had tested the beetles for their ability to feed on plants of some
35 families. The tests included several species of
Hypericum
, on which
some of the beetles survived and reproduced. Additional testing was done
by American scientists, although none was done with species of
Hyper-
icum
. Canadian scientists also tested the feeding preferences of the beetles
and found that species of
Hypericum
were accepted as food plants. Despite
the evidence that the beetles could feed on various species of
Hypericum
,
all three beetles were approved and released in Canada and the United
States in the late 1940s (Harris 1988).
One of the beetles,
Chrysolina quadrigemina
,proved to be an effective
control agent for common St. John's wort. In 1975, however,
C. quadrigem-
ina
was found to be attacking an introduced horticultural plant, creeping
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