Contents - Faperta

494 Biotechnological Approaches for Pest Management and Ecological Sustainability
Combining genomics with high-throughput biochemical screening and combinatorial
chemical approaches to generate extensive arrays of compounds for screening will lead to
a range of new chemicals for pest control. The adoption of such approaches by the pharmaceutical
industry has permitted screening rates of up to 10,000 molecules a day.
The new tools involving combinational synthesis, high throughput, and in vitro screening
has become an integral part of discovering new chemicals for agriculture (Hess, Anderson,
and Reagan, 2001). Depending on the synthesis design, the products of combinational
synthesis, referred to as a library, can be biased toward an intended target. Unbiased
libraries are prepared to maximize chemical diversity around a central core. Compounds
in biased libraries are rationally designed to contain structural motifs for pharmacophores
that are presumed to be benefi cial for activity on the intended target. The compounds can
be screened on microtiter plates having 96 to 864 wells. For in vitro assays, high-density
formats are preferred that allow for testing higher concentrations. This leads to rapid identifi
cation of active molecules. A wide range of in vitro or in vivo assays can be conducted
for a range of pesticides using microtiter plates.
Another application of molecular biology is the development of novel strains of entomopathogenic
bacteria, fungi, nuclear polyhedrosis viruses, and nematodes. Recombinant
Bacillus thuringiensis (Berliner) strains with enhanced toxicity and broad insecticidal spectrum
have been developed for pest management (Kaur, 2004). To increase the persistence
of insecticidal crystal proteins (ICPs), alternative modes of delivery through Pseudomona
sp. and endophytes have also been developed. The ICPs have been modifi ed by site-
directed mutagenesis to improve their insecticidal effi cacy, while the yield of ICPs has
been increased through the use of strong expression promoters and other regulatory elements.
Gene disabling of the sporulation-specifi c proteases has resulted in increased yield
of ICPs. Development of a ligand-mediated system can be used for structure and function
analysis of pesticides based on ecdysone (a hormone that regulates molting in insects)
(Tran et al., 2001). Such a system could provide a tool for structure function analysis of
ecdysone receptor (ECR) in relation to ecdysteroids and other known analogs, and can be
used as an effective means for screening new chemicals, and to validate and improve
potential insecticidal molecules.
Molecular Markers for Monitoring Insect Resistance to Insecticides
Genomic technologies are now allowing investigation of some previously intractable
resistance mechanisms. These cover resistance to both synthetic insecticides and biopesticides.
The molecular techniques permit fundamental insights into the nature of mutations
and genetic processes (gene amplifi cation, altered gene transcription, and amino acid
substitution) underpinning resistance and other adaptive traits. This in turn will lead to
high-resolution diagnostics for resistance alleles, in both homozygous and heterozygous
forms, especially for insect pests with multiple resistance mechanisms, or for resistance
mechanisms not amenable to biochemical assays. Evolution of insecticide-resistant insects
provides evolutionary biologists an ideal model system for studying how new adaptations
can be rapidly acquired. There is, therefore, a great interest in the use of tools of molecular
biology to elucidate the mechanisms of resistance to insecticides.
Recent studies have shown how genomic techniques can access mechanisms that had
previously proven intractable to molecular analysis (Gahan, Gould, and Heckel, 2001;