Contents - Faperta

Applications of Biotechnology in Agriculture: The Prospects 33
essential insect proteins, which serve as control agents against nematodes, pathogens, and
viruses (Van Engelen et al., 1994; Rosso et al., 1996). This approach of controlling insects
would offer the advantage of allowing some degree of selection for specifi city effects,
so that insect pests but not the benefi cial organisms are targeted. The development of a
delivery system from transgenic plants to the insect hemolymph will remove a key constraint
in the transgenic approach to crop protection.
Genetic Improvement of Entomopathogenic Microorganisms
Genetic engineering can also be used to improve the effi cacy of entomopathogenic microorganisms.
Efforts to improve B. thuringiensis have largely been focused on increasing its
host range and stability (van Frankenhuyzen, 1993). The toxin gene from B. thuringiensis
has been inserted in Pseudomonas fl uorescens Migula. The recombinant bacteria are fermented
and then killed for application on crops for pest management. Work on baculoviruses
is focused on incorporation of genes that produce the proteins that kill the insects at
a faster rate (Bonning and Hammock, 1992), and on removal of the polyhedrin gene, which
produces the protective viral-coat protein, and its persistence in the fi eld (Corey, 1991).
Spiders and scorpions produce powerful neurotoxins that have been expressed in transgenic
organisms (Barton and Miller, 1991). Genes encoding neurotoxins from predatory
mites (Tomalski and Miller, 1991) and scorpion (Stewart et al., 1991) have also been deployed
in recombinant baculoviruses to increase their biological activity. Incorporation of benomyl
resistance into the entomopathogenic fungus, Metarhizium anisopliae (Mets.) Sorokin
could make this fungus more useful for use in integrated pest management (Goettel et al.,
1990). The insect-specifi c neurotoxin AaIT from the venom of the scorpion, Androctonus
australis Hector expressed in tobacco has shown insecticidal activity against H. armigera
larvae (up to 100% mortality after 6 days) (Yao et al., 1996). Transgenic plants of tobacco
have been obtained containing an insecticidal spider peptide gene, and some of these
plants have shown resistance to H. armigera (Jiang, Zhu, and Chen, 1996). The role of neurotoxins
from insects and spiders need to be studied in greater detail before they are
deployed in other organisms and plants because of their possible toxicity to mammals.
Genetic Improvement of Natural Enemies
There is tremendous scope for developing natural enemies with genes for resistance to
pesticides and ability to withstand adverse weather conditions (Hoy, 1992). One of the
major problems in using natural enemies in pest control is the diffi culty involved in mass
rearing, and ability to withstand adverse conditions, and biotechnology has the promise
to solve many of these problems. It can also help to understand the genetics and physiology
of reproduction, and control of sex ratio in natural enemies. This information can be
used to improve rearing of the natural enemies for biological control. Biotechnological
interventions can also be used to broaden the host range of natural enemies or enable
their production on artifi cial diet or nonhost insect species that are easy to multiply under
laboratory conditions.