Insect Control: Biological and Synthetic Agents - Index of

acetyltransferase gene. Second, they generated
a recombinant AcMNPV (vHsp-1) that expressed a
second copy of the ie1 gene under the constitutively
expressed hsp70 promoter. Both of these approaches
generated genetically modified AcMNPVs with
host ranges that extended to S. littoralis.
At present, overexpression of AcMNPV ie1 and
insertion of LdMNPV hrf-1 into the AcMNPV
genome are the only ways in which the host
range of AcMNPV can be extended to include pest
insect species. Other AcMNPV genes that are
involved in extending host range or dramatically
increasing virulence include p35 (Clem et al.,
1991; Hershberger et al., 1992; Clem and Miller,
1993; Griffiths et al., 1999), the DNA helicase gene
p143 (Maeda et al., 1993; Croizier et al., 1994),
host cell specific factor 1 (hcf-1; Lu and Miller,
1995), late expression factor 7 (lef-7; Lu and Miller,
1995), and immediate early gene 2 (ie2; Prikhod’ko
et al., 1999). The roles of these genes in host range
expansion and increase of virulence is discussed in
the previous chapter.
10.5. Safety of GM Baculoviruses
The safety of a synthetic chemical or biologically
based pesticide can never be assured with absolute
confidence. Thus, when society considers whether
or not a new pesticide is ‘‘safe,’’ a better question to
ask might be: What level of risk are we as a society
willing to accept for a given benefit? In the case of
chemical pesticides, the general public and a wide
array of researchers (scientists, medical doctors,
governmental regulators, statisticians, pathologists,
ecologists, etc.) have analyzed the actual,
potential, and perceived risks that they pose to
human health and the environment. In general, all
of these stakeholders agree that the benefits of
chemical pesticides sufficiently outweigh any shortor
long-term risks that they may pose. Society is thus
willing (and should be willing) to accept some level
of risk for a given benefit (e.g., increased yields of
food, fiber, and feed from a given amount of natural
resource). There are of course instances in which
society has determined that the costs and risks associated
with a particular pesticide (e.g., DDT) outweigh
the benefits. In terms of the use of a GM
baculovirus pesticide, this leads us to the following
questions: (1) what are the risks associated with the
field release of a GM baculovirus? (2) are these risks
worth the benefits? and (3) are these risks any
greater than the risks associated with the use of a
chemical insecticide? A number of research studies
and essays have addressed the first question. Miller
10: Genetically Modified Baculoviruses for Pest Insect Control 361
(1995) and Hails (2001) suggest that the primary
focus of assessing the risks of the field release of
a GM baculovirus should include:
1. How the GM baculovirus affects nontarget
species.
2. Whether the introduced gene provides a selective
advantage to viral replication, survival, and/or
host range (i.e., is fitness improved).
3. Should the introduced gene transfer to another
organism, will this event provide a selective
advantage to that organism.
10.5.1. Potential Effects of a GM Baculovirus
on Nontarget Species
The potential of natural and recombinant baculoviruses
to induce a deleterious effect upon vertebrates
has been extensively studied (Burges, 1981;
Black et al., 1997). More than two dozen different
baculoviruses have been tested in a wide range of
vertebrates including 10 different mammalian species,
birds, and fish. The baculoviruses in these tests
were administered by various routes including inhalation,
topical application, injection (intravenous,
intracerebral, intramuscular, intradermal), and orally.
Baculovirus induced deleterious effects were not
observed in any of these tests. Direct and indirect
tests on human subjects have also been conducted
including oral administration of high (greater than
10 9 polyhedra) doses of polyhedra of HzSNPV over
a period of 5 days (Heimpel and Buchanan, 1967).
The blood of workers who were involved in the
production of HzSNPV during a 26 month long
period was analyzed for infectious baculovirus,
baculoviral antigens, or baculoviral antibodies –
none were detected (Black et al., 1997). Furthermore,
the ubiquitous baculovirus load from foods
in our diet may be quite high (Heimpel et al., 1973;
Thomas et al., 1974). For example, Heimpel et al.
(1973) found that a square inch (approximately
6.5 cm 2 ) of cabbage taken from a store shelf may
contain up to 2 10 6 polyhedra suggesting that
consumption of a single serving of coleslaw (16 in 2
of cabbage) exposes us to up to 3.2 10 7 polyhedra.
These studies indicate that we live under constant
exposure to baculoviruses with no apparent deleterious
effects. The lack of deleterious effects is not
completely unexpected since polyhedra are extremely
insensitive to the neutral or acidic pH conditions
of the vertebrate digestive system. Thus, any polyhedra
that are normally ingested while eating coleslaw,
for example, pass through the digestive tract
and are either excreted intact or should any ODVs
be released they are quickly inactivated first by
the action of pepsin at low pH and subsequently