Baculoviruses are a family of arthropod-specific viruses found ubiquitously
in the environment and have been isolated from more than
600 host insect species including the orders Lepidoptera, Hymenoptera,
Diptera, Orthoptera, Coleoptera, Neuroptera, Thysanera, and Trichoptera
(Adams and McClintock, 1991; Herniou et al., 2003; Larsson, 1984;Martignoni and Iwai, 1986;Murphy et al., 1995; Tinsley and Kelly, 1985).
Most baculovirus species have been isolated from Lepidoptera and the
majority of nonlepidopteran isolates have not been well characterized.
They are DNA viruses with closed, circular, double-stranded DNA genomes
ranging from 80 to 180 kbp in size. The genomes are packaged in
bacillus-shaped nucleocapsids, and the name “baculovirus” is in reference
to the nucleocapsid shape. Presently, the genomes from 29 baculovirus
species have been sequenced providing a database of more than
4000 genes (Hiscock and Upton, 2000).
Baculoviruses play an important ecological role regulating the size of
insect populations (Evans, 1986; Odindo, 1983). For many decades, baculoviruses
have been applied as targeted biocontrol agents against
forestry and agriculture pests. Baculovirus insecticides have been
effective against insect pests such as velvetbean caterpillar (Anticarsia
gemmatalis) (Moscardi, 1999), cotton bollworm (Helicoverpa zea)(
Zhang, 1994), and gypsy moth (Lymantria dispar) (Cook et al., 2003).
Baculovirus-based biocontrol applications have been restricted to
lepidopteran and hymenopteran (sawflies) pests. Mosquito-specific baculoviruses
have been characterized (Andreadis et al., 2003; Moser et al.,2001) with the potential to develop them for biocontrol of mosquitoes.
Baculoviruses are transmitted to insects by the oral route mediated
by the occlusion-derived virus (ODV). This is reference to the occlusion
of orally infectious baculoviruses in protein crystals called occlusion
bodies (OBs). It is important to study the structure and function
of ODVs and OBs because it expands the horizon for the application
of baculovirus as insecticides. The ODV is also specialized to exploit
the insect midgut which is one of the most extreme biological environments
where the viruses are subject to caustic pH and digestive
proteases. Understanding the molecular biology of the ODV should
reveal new frontiers in protein chemistry. Finally, ODVs establish
infection in insect gut tissues that are virtually nonsupportive to virus
replication and which are continuously sloughed away. ODVs carry
with them a battery of proteins that enable them to rapidly exploit and
harness these unstable cells for virus replication. Learning about these
proteins will have implications in biocontrol and biotechnology.