Biology Reference
In-Depth Information
Evolutionary Adaptation by Biological
Control Species
In a few instances, herbivorous alien arthropods introduced for biocontrol
have adapted evolutionarily to nontarget plants, as we noted in the intro-
ductory example. Such examples are still uncommon, and some entomol-
ogists (see, e.g., van Klinken and Edwards 2002) have argued that only the
potential for altered frequency of use of existing hosts needs to be con-
sidered in risk assessment of introduction of a biocontrol species. Accord-
ing to them, fundamental shifts in host range are very unlikely and do not
need to be considered. Nevertheless, considering the patterns of adapta-
tion shown by similar native arthropods to alien plants (chapter 13), the
potential for such adaptation seems appreciable. That biotypes specific to
related host species are known for some biocontrol agents (see, e.g., Hoff-
mann et al. 2002) indicates that evolutionary adaptation to related hosts
can occur.
Alien biocontrol species have also shown evolutionary adaptation to
conditions of their new habitat. Studies of a nonnative parasitoid and its
prey show that rapid evolution can occur in relation to habitat conditions.
In North America, the small cabbage white butterfly (
Pieris rapae
), itself an
alien introduced from Europe, is parasitized by a wasp (
Cotesia glomerata
)
that was introduced from Europe in the late 1800s as a potential biolog-
ical control agent. In North America, the butterfly feeds on a variety of
plants of the Brassicaceae, both native and introduced. Some of these
plants, such as cabbage (
Brassica oleracea
), are cultivated in monoculture,
whereas others grow wild as individuals or small clusters in diverse stands
of herbaceous vegetation. Van Nouhuys and Via (1999) examined the
behavior of
Cotesia
wasps from cabbage fields and wild vegetation under
laboratory conditions.Wasps from the two habitats differed in behavior in
test situations simulating cabbage fields. Wasps from the wild vegetation
switched locations more often than wasps from cabbage fields, suggesting
that cabbage-field wasps had evolved to be more sedentary because suit-
able host plants for their butterfly prey were close together. Furthermore,
Van Nouhuys andVia (1999) were able to show that these differences had
a genetic basis.
In Australia, the moth
Cactoblastis cactorum
was introduced from
Argentina in 1925 as a biological control agent for prickly pear cacti
(
Opuntia
spp.). This moth typically has two generations per year in
Argentina and exhibits this pattern in Queensland and New South Wales,
where it has become very widely established. Sometime between 1945
