Biology Reference
In-Depth Information
ing on foliage. Thus, the richness of the insect fauna on this species in
Canada approaches that in Europe.
In spite of the rapid accumulation of pests by many introduced species,
the time to fully exploit hosts is often much longer (Strong 1979). Kogan
(1981), for example, found that in Asia, the native home of soybean
(
Glycine max
), the phytophagous arthropods of this plant feed in ways that
include all those used by soybean arthropods in North America as well as
several additional modes.
Several good examples are available of alien plants that native phy-
tophages have not fully exploited. Scotch broom (
Cytisus scoparius
), intro-
duced to North America from the British Isles, is a highly invasive shrub
in the Pacific Northwest. In Britain, this shrub hosts a rich assemblage of
specialist herbivores, including 23 species of insects that feed on the plant's
pods and seeds. A survey in 1963 (Waloff 1966) recorded only 17 species
of herbivorous insects on Scotch broom at sites in California and British
Columbia. No pod or seed feeders were recorded at these North Ameri-
can sites.The lack of seed- and pod-feeders on Scotch broom in Califor-
nia and British Columbia (Waloff 1966) shows that North American
insects have not yet exploited this plant to the degree that British insects
have. Memmott et al. (2000) examined Scotch broom in New Zealand
and Australia and compared the invertebrate fauna to broom in France
and England, where the species is native. Specialist phytophages were also
deficient in New Zealand and Australia, especially those feeding on flow-
ers and seeds.
Yellow starthistle (
Centaurea solsticialis
), native to Eurasia, is an invasive
rangeland weed that was introduced to North America in the early or
mid-1800s. It is now present on more than 3 million ha in the northern
intermontane region of North America. In Idaho, a survey of the insect
fauna associated with the plant revealed numerous species that used nec-
tar or pollen but only eight native insects that fed on the foliage of the
plant (Johnson et al. 1992). Only two of these were regularly present. In
contrast, in southern Europe, Clement (1990) found 42 species of herbiv-
orous insects feeding on yellow starthistle. At least 18 of these species
were specialists for yellow starthistle or close plant relatives. Similar obser-
vations were made by Wolfe (2002) for white campion (
Silene latifolia
), a
widespread noxious weed native to Europe.
The colonization of alien plants by native herbivores is clearly influ-
enced by the taxonomic relatedness of alien plants with native plants.This
is shown by the speed at which sawtooth oak was colonized by leaf-min-
ing insects at Tall Timbers Research Station in Florida. In England, the
