Contents - Faperta

304 Biotechnological Approaches for Pest Management and Ecological Sustainability
be made repeatedly. Because of these problems, a number of alternatives have been proposed,
including hybrid sterility and cytoplasmic incompatibility (Whitten, 1985), chromosomal
translocations (Serebrovsky, 1940), and conditional lethal traits. The conditional
lethal system was fi rst proposed by LaChance and Knipling (1962). As the conditional
lethal genes become effective only under certain conditions, there is suffi cient chance for
the gene to spread into the wild populations. The conditional lethal gene could be temperature
dependent or results in failure to diapause. The female killing system using a
y-linked translocation can achieve better control than the SIT (Foster, 1991). Release of
insects carrying a dominant lethal (RIDL) gene has been proposed as an alternative to the
conventional techniques used for insect sterilization (Thomas et al., 2000; Alphey and
Andreasen, 2001; Schliekelman and Gould, 2000a, 2000b). It is based on the use of a dominant,
repressible, female-specifi c gene for insect control. A sex-specifi c promoter or enhancer
gene is used to drive the expression of a repressible transcription factor, which in turn
controls the production of a toxic gene product. A non-sex-specifi c expression of the repressible
transcription factor can also be used to regulate a selectively lethal gene product.
Insects produced through genetic transformation using this approach do not require sterilization
through irradiation, and can be released in the ecosystem to mate with the wild
population to produce the sterile insects, which will be self-perpetuating. Notch60g11 is a
sex-linked mutation in D. melanogaster that causes dominant, cold-sensitive lethality in
heterozygous embryos (Fryxell and Miller, 1995). A population of normal D. melanogaster
has been driven to extinction by adding an equal number of homozygous Notch60g11
mutants to each of three successive generations at 18°C. Notch60g11 homozygotes reared at
26°C showed normal viability and mating success, even in competition with a wild-type
insect population, presumably because of the developmental stage-specifi city of the
Notch60g11 mutation. Because Notch60g11 is a frame shift mutation in a gene that is highly
conserved in arthropods and vertebrates, this autocidal biological control strategy could
be used in any insect species that reproduces sexually and lives in a temperate climate.
Markers and Promoters
Some genes are useful for identifying transformants, including microbial genes such as
neomycin or G418 resistance, chloramphenicol acetyltransferase (CAT ), and b-galactosidase.
Relatively few genes cloned from Drosophila can be used directly for transforming benefi cial
arthropods, but they could serve as probes for homologous sequences in other arthropods.
Expression of transgenes can be regulated by using different promoters. Many people have
used the heat shock protein hsp70 from D. melanogaster to allow temporal control of gene
expression with a change in temperature. Tissue-specifi c expression has been achieved with
Apyrase in mosquito salivary glands. The ug promoter has been used to drive the expression
of an agent with anti-Plasmodium activity, a blood meal triggered expression of antipathogen
factors in mosquito fat-bodies (Kokoza et al., 2000). Carboxypeptidase promoters can be
used to drive blood inducible gene expression in A. aegypti (Moreira et al., 2000).
Genetic manipulation through DNA-mediated genetic transformation also requires a
reliable genetic marker. The use of the polymerase chain reaction (PCR) to identify DNA
markers, particularly markers identifi ed by a random sample of the genome, such as random
amplifi ed polymorphic DNA (RAPD), offers a highly effi cient method for detecting
genetic changes in arthropod populations (Arnheim, White, and Rainey, 1990; Williams