Insect Control: Biological and Synthetic Agents - Index of

10 Genetically Modified Baculoviruses
for Pest Insect Control
S G Kamita, K-D Kang, and B D Hammock,
University of California, Davis, CA, USA
A B Inceoglu, Ankara University, Ankara, Turkey
ß 2010, 2005 Elsevier B.V. All Rights Reserved
10.1. Introduction 331
10.2. Insertion of Hormone and Enzyme Genes 333
10.2.1. Hormones 333
10.2.2. Juvenile Hormone Esterase 335
10.2.3. Proteases 338
10.2.4. Other Enzymes and Factors 340
10.3. Insertion of Insect Selective Toxin Genes 341
10.3.1. Scorpion Toxins 341
10.3.2. Mite Toxins 345
10.3.3. Other Toxins 346
10.3.4. Improvement of Toxin Efficacy by Genetic Modifications 347
10.3.5. Toxin Interactions with Chemical Pesticides 354
10.4. Modification of the Baculovirus Genome 355
10.4.1. Deletion of the Ecdysteroid UDP-Glucosyltransferase Gene 355
10.4.2. Removal of Other Nonessential Genes 358
10.4.3. Alteration of Host Range 359
10.5. Safety of GM Baculoviruses 361
10.5.1. Potential Effects of a GM Baculovirus on Nontarget Species 361
10.5.2. Fitness of GM Baculoviruses 364
10.5.3. Movement of the Introduced Gene to Another Organism 366
10.6. Field Testing and Practical Considerations 366
10.7. Concluding Remarks 367
10.1. Introduction
There are presently more than 20 known groups of
insect pathogenic viruses, which are classified into
12 viral families (Tanada and Kaya, 1993; Blissard
et al., 2000). Among insect pathogenic viruses, members
of the family Baculoviridae are the most commonly
found and most widely studied. Baculoviruses
are rod shaped, enveloped viruses with large,
covalently closed, double-stranded DNA (dsDNA)
genomes. Baculoviruses are made up of two genera:
nucleopolyhedrovirus (NPV) and granulovirus
(GV). The NPVs can be further divided into two
groups (I and II) on the basis of the phylogenic
relationships of 20 distinguishing genes (Herniou
et al., 2001). Baculoviruses produce two phenotypes,
the budded virus (BV) and the occluded
virus (OV), during their life cycles (Granados and
Federici, 1986; Miller, 1997). BVs are predominantly
produced during an early phase of infection
and acquire their envelopes as they bud through the
plasma membrane. BVs are responsible for the systemic
or cell-to-cell spread of the virus within an
infected insect. Continuous cell lines that support
high-level production of BVs are available for
NPVs, but not for GVs. The availability of these
cell lines has been critical for the development of
genetically modified NPVs. OVs are produced
during a late phase of infection and are involved
in the horizontal or larva-to-larva transmission
of the virus. The OV of the NPV is known as a
polyhedron (plural polyhedra) or polyhedral inclusion
body, and that of the GV is known as a granule.
Within the proteinaceous crystal matrix of the
OV are embedded virions termed the occlusion
derived virions (ODVs). Each ODV is formed by
single or multiple nucleocapsids surrounded by an
envelope. In the field, the polyhedron or granule
structure protects the embedded ODV(s) from the
environment.
Owing to their inherent insecticidal activities,
natural baculoviruses have been used as safe and
effective biopesticides for the protection of field
and orchard crops, and forest in the Americas,
Europe, and Asia (Black et al., 1997; Hunter-Fujita