Contents - Faperta

276 Biotechnological Approaches for Pest Management and Ecological Sustainability
Genetic improvements in entomopathogenic nematodes may expand their potential as
biocontrol agents by increasing search capacity, virulence, and resistance to environmental
factors (Burnell and Dowds, 1996; Gaugler and Hashmi, 1996). Heat-shock-resistant protein
has been inserted in Heterorhabditis bacteriophora Poinar, which is 18 times better than
the wild types in surviving at high temperatures (Gaugler, Lewis, and Stuart, 1997; Gaugler,
Wilson, and Shearer, 1997).
The approach of improving the effi cacy of existing biological control agents has recently
been extended to nematodes that live in a symbiotic relationship with bacteria. When the
nematodes invade a specifi c insect host, the bacterium Xenorhabdus is released in the insect,
thereby killing the insect within two days (Poinar and Thomas, 1966). The bacterium is
believed to kill the insect by producing a specifi c toxin and attempts have been made to
clone the gene responsible for producing the toxin. The aim is to engineer a more effective
toxin that can be delivered by the nematode. Although nematodes must still be produced
commercially using live insect hosts, this has not negated their potential utility in IPM
systems. Research currently underway is focused on determining the best techniques for
application of nematodes in crop and orchard systems. The major problem is the sensitivity
of nematodes to environmental conditions. A detailed knowledge of the ecology and
behavior of the nematodes and their hosts is likely to provide solutions to this problem.
Biosafety Considerations for Using Genetically Engineered Microbes
Biopesticides are often developed from species that are ubiquitous in natural environments.
Residual effect of the biopesticides is thus of less importance. Therefore, the regulatory
criteria used for their release as commercial products may not be as stringent as for synthetic
chemicals. However, their effects on benefi cial insects, allergenicity, and pathogenicity
to humans must be evaluated. Risk assessment for genetically engineered microorganisms
includes the probability of dissemination of the genetic material to the indigenous microbes
and to other organisms, the risk of being expressed differently, and change in the level of
gene expression due to mobilization of transfer defi cient plasmids or self-transfer. To study
this aspect, self-transmissible and non-self-transmissible plasmids have been created,
which carry resistance to trimethoprin and sulfonamide. These plasmids are of immense
value in assessing the survival and transfer of genetic material under natural conditions
(Cuskey, 1992; Levin, 1995; Tzotzos, 1995). Addition of large amounts of genetic material
into organisms increases the likelihood of mutations, and if the genetic material is
exchanged with the indigenous microbes, the chances of mutation will also increase.
Genetic engineering results in many more copies of the genetic material in signifi cant
amounts in different species and increases the probability of gene transfer and mutation.
To limit the exchange of genetic material, plasmids have been produced by changing the
nucleotide sequences that are unable to function in the exchange process and prevent the
transfer of genetic material into select hosts. However, under certain circumstances, helper
plasmids can enter the cell and mobilize the disarmed plasmid (Zylstra, Cuskey, and Olson,
1992). Risk associated with the use of genetically engineered biopesticides requires the
identifi cation of the hazard involved and the level of exposure, stability, persistence in
nature, transferability, effective dosage, virulence, potency, and the host range.
Biopesticides are employed with the sole purpose of inhibiting the growth or reproduction
of insect pests or causing immediate death. They are modifi ed either to increase their