Biology Reference
In-Depth Information
mechanism for introducing cytoplasmic factors into natural populations.
This may eventually be useful for introducing deleterious factors into pest
insect populations.” Unfortunately, this is the only example to date in which
Wolbachia
has been shown to “sweep” through a
very large
population in the
field, so it is unclear whether such sweeps will occur with other species and
with other strains of
Wolbachia
.
Reproductive incompatibility could be transferred to a population of insects
lacking
Wolbachia
by microinjection of transgenic
Wolbachia
, mass rearing the
infected individuals, and release of the insects into natural populations (
Sinkins
and O'Neill 2000
). Several questions must be resolved, including whether resis-
tance to the cytoplasmically transmitted organisms could develop in the pest
insect populations if the invasion by
Wolbachia
takes a “long” time, whether
such incompatibility will be stable, and whether the
Wolbachia
will move hori-
zontally to nontarget insect species. Appropriate release rates of individuals
containing the
Wolbachia
are critical or the drive system can fail to function
(
Turelli and Hoffmann 1991
). A description of releases of the mosquito
Aedes
aegypti
containing novel
Wolbachia
strains is described in
Box 14.3
.
Deployment of genetically manipulated arthropods is complicated if some
form of reproductive isolation or drive mechanism cannot be provided when the
goal is to obtain population replacement or character replacement. One of the
reasons genetically modified predatory mites were successfully used in a pest-
management program may be because these natural enemies disperse relatively
slowly (
Hoy 2000a,b
). Releases of pesticide-resistant strains of natural enemies
into pesticide-treated orchards or vineyards provided sufficient isolation that
the genetically manipulated strains were able to establish without extensive
competition from, or interbreeding with, susceptible native populations (
Caprio
et al. 1991
). Likewise, releases of a pesticide-resistant strain of the parasitoid
Aphytis melinus
into Israeli citrus groves did not involve competition or inter-
breeding with susceptible populations because this species was not present in
Israel. Selection with pesticides for the resistant population could provide the
“drive” mechanism.
Predicting whether, and how, genetically modified pest or beneficial arthro-
pods will establish is difficult (
Hoy 2000a,b
). There are at least two models that
could be used in the establishment of a genetically modified strain in situa-
tions in which a “native” population exists: 1) the released strain displaces the
“native” population and replaces it (replacement model). This model assumes
relatively little interbreeding occurs between the released and “native” popula-
tions. 2) Alternatively, the released strain interbreeds with the “native” popula-
tion and a hybrid population is produced. By appropriate strong selection, the
