Biology Reference
In-Depth Information
One of the most extensive examples of biocontrol agents attacking
nontarget animal species involved parasitoids introduced to the Hawaiian
Islands for control of lepidopteran pests. On the island of Kauai, Hawaii,
122 species of wasp and fly parasitoids have been introduced over the past
century (Henneman and Memmott 2001).These parasitoids have attacked
many native species of moths, even in the remote highland forests. Of
more than 200 parasitoid individuals reared from caterpillars collected in
the Alakai Swamp wilderness preserve, 83% were species deliberately
introduced for biological control and an additional 14% were alien species
that were not deliberately introduced.The overall incidence of parasitism
of native moth caterpillars was estimated at 19-22%. Since the parasitoids
involved have been present in Kauai for many years, these moth species
are probably not endangered. Whether or not other species of native
moths have become extinct because of parasitism by alien parasitoids is
not known. In other parts of the Hawaiian Islands, biological control
introductions are considered to be responsible for extinctions of at least
15 native moth species (Howarth and Ransey 1991). Fortunately, some
distinctive groups of native moths, including forms that are uniquely car-
nivorous, have not been attacked by alien parasitoids.
Only a few true predators have been introduced for biological con-
trol, but almost all use nontarget species, in some cases to a greater extent
than target species. Mosquitofish (
Gambusia
spp.), widely introduced for
mosquito control, prey on many other small aquatic vertebrates (McEvoy
1996). The cane toad (
Bufo marinus
), privately introduced to Australia
(Samways 1997), has proven to be a serious predator on many native fish
and amphibians.The impacts of introduced mongooses on oceanic islands
were discussed in chapter 16.
A recent example that has been studied in detail illustrates the risks of
introduction of herbivorous insects for the control of problem plants.
Musk thistle (
Carduus nutans
) is one of the troublesome Eurasian thistles
that have been introduced to North America. It is now known from
almost all of the contiguous United States. After screening for its ability
to use various native North American thistles, a weevil (
Rhinocyllus coni-
cus
) was judged to be a potentially effective biological control agent for
musk thistle and one that would probably not attack native thistles of the
genus
Cirsium
to a significant degree. Beginning in the early 1970s,
R. con-
icus
was released in various areas where major infestations of musk thistle
occurred.
By the late 1980s, however,
R. conicus
had begun to attack many native
thistles (Louda et al. 1997; Louda 1998). In 1993, for example, it was
