Biology Reference
In-Depth Information
prickly pear cactus (
Opuntia
spp.). This moth, introduced to the West
Indies, dispersed by natural means to the Florida Keys in 1989. There, it
began to attack several native
Opuntia
species (Samways 1997). By 2002,
Cactoblastis
had spread in coastal areas throughout the Florida peninsula,
west to St. George Island in the Florida Panhandle, and north to near
Charleston, South Carolina (Hight et al. 2002). It is unlikely that spread
of this insect can be prevented to areas of the western United States and
Mexico, where numerous species of
Opuntia
, both wild and cultivated,
exist. Clearly, many biocontrol arthropods have a considerable dispersal
capacity that must be considered when introductions are made.
In a few cases, biocontrol herbivores have extended their feeding to
plants distantly related to their target species. The lace bug (
Teleonemia
scrupulosa
) has been introduced in many countries as a biocontrol for lan-
tana (
Lantana camara
), a plant of the family Verbenaceae that is a trouble-
some weed in tropical regions. In East Africa, the lace bug was found to
attack one variety of cultivated sesame (
Sesamum indicum
) belonging to a
different family, Pedaliaceae (Harris 1988; Hokkanen and Pimentel 1989).
In Hawaii, this same bug has also been found to attack a small native tree
known as naio (
Myoporum sandwicense
), a member of the family Myopo-
raceae. Another case involves a weevil (
Neochetina eichhorniae
) introduced
for control of water hyacinth (
Eichhornia crassipes
) in the southern United
States. This weevil has been found to attack plants of at least two other
families (Harris 1988).
Host shifts by introduced predators and parasites have led to negative
impacts on native species, as well as on some other biocontrol species.
Introductions of vertebrate predators, such as mosquitofish (
Gambusia
spp.), the small Indian mongoose (
Herpestes javanicus
), and the cane toad
(
Bufo marinus
) for control of various pests have led to severe impacts on
native freshwater and terrestrial vertebrates. Introduction of parasitic
insects and predatory molluscs to Hawaii and other Pacific islands has
caused the endangerment or extinction of many native arthropods and
molluscs.We have examined these cases in detail in chapter 16.
Alien biocontrol species can create impacts throughout the food web
in which target or nontarget hosts are enmeshed. On Platte thistle (
Cir-
sium canescens
), the weevil
Rhinocyllus conicus
, for example, may negatively
influence populations of other thistle insects that attack other, weedier
thistles later in the summer (Louda and Arnett 2000). One species of
introduced parasitoid has also caused an indirect negative effect by hyper-
parasitism of another parasitoid that had been introduced for biological
control (Flanders 1943).
