Contents - Faperta

Genetic Engineering of Natural Enemies for Integrated Pest Management 307
with the hypothesis that transposable elements can move between different species and
orders of arthropods (Kidwell, 1992; Robertson, 1993).
Horizontal Gene Flow
If horizontal transmission of DNA (or microorganisms) between arthropods occurs, even
if exceedingly rarely, there is no guarantee that genes inserted into one species will be
completely stable. Naturally occur ring horizontal transmission of DNA between species
may have provided some of the variability upon which evolution has been based, but the
extent and nature of this naturally occurring gene transfer are just being determined. The
release of transgenic arthropods will have to be evaluated on the basis of probable benefi ts
and potential risks. Horizontal gene transfer should be taken seriously while considering the
release of transgenic arthropods, and such a risk is more associated with the use of transposable
elements. The hobo transposable element spreads through D. melanogaster (Pascal
and Periquet, 2003). Laboratory experiments have demonstrated the ability of P-elements
to spread rapidly to populations in which they were absent (Good et al., 1989). The transposable
element mariner probably spreads horizontally between insects (Robertson and
Lampe, 1995). Little is known about the transfer of gut symbionts horizontally, but it occurs
over a short span of time in insects sharing common food sources (Huigens et al., 2000).
Baculoviruses are capable of incorporating genes from the host genome (Fraser et al., 1995),
but such a route has not been demonstrated convincingly. Risk assessment for transgenic
insects is complicated by our inability to judge the possibilities for horizontal gene
transfer, and the level to which the harm may occur.
Transgene Instability
Stability of the introduced gene is necessary to ensure that the transgenic population will
carry the gene with adequate expression, and that the released population will not pose a
hazard to the environment. Transposable elements have the ability to move within the
insect genome, and this may infl uence the stability of the introduced gene if the transposable
element is used from the same family as the vector (O’Brochta and Atkinson, 1996).
Hermes and hobo transposable elements belong to the same hAT family, although their transposase
elements are only 55% identical (Sundararajan, Atkinson, and O’Brochta, 1999).
There were no differences between a wild type and genetically modifi ed population of
M. occidentalis in daily egg production, hatchability at three temperatures (28.5, 33.5, and
38.2°C) and four relative humidities (32.5, 75.5, 93, and 100% RH), diapause incidence, or
proportion of female progeny produced. Eggs did not hatch at 38°C with any of the relative
humidities tested, or at 33.5°C with 100% RH (Li and Hoy, 1996). Metaseilus occidentalis did
not survive on leaves of Phaseolus vulgaris L., Citrus jambhiri Lush., Zea mays L., Lycopersicon
esculentum Mill., Capsicum annuum L., or Hedera helix L. without prey or on a diet of pollen
alone. Adult females did not survive on eggs and larvae of Papilio cresphontes Cramer and
Eurema daira (Godart). As no signifi cant differences between the transgenic and wild-type
strains were found for the traits tested, the transgenic strain is not expected to exhibit any
new biological attributes in a short-term fi eld release. Genetic manipulation of phytoseiid
species has yielded transgenic strains, but none have been released into the environment
(McDermott and Hoy, 1997). Previous data suggested that M. occidentalis could not survive
the wet humid summer season. A nontransgenic strain of M. occidentalis has been released
on soybean plants infested with T. urticae. CLIMEX, a population growth model that uses
climatic factors to determine whether a given poikilothermic species can colonize and