Ph. D. Scholar Department of Entomology Indira Gandhi Krishi Vishwavidyalaya Raipur (Chhattisgarh)

1. SCOPE OF GENETIC ENGINEERED
MICROBES AND PARASITOIDS IN
BIOLOGICAL CONTROL
Prepared By
Aaliya Afroz
Ph. D. Scholar
Dept. of Entomology, IGKV, Raipur

2. GENETIC ENGINEERING OF PREDATORS AND
PARASITOIDS
◦ Genetic improvement of arthropod natural enemies to enhance their
capacity to control pests has been achieved previously by artificial
selection (Beckendorf and Hoy, 1985; Johnson and Tabashnik, 1994).
◦ An integrated pest management program featuring a predatory mite
strain selected for insecticide resistance has been successfully
implemented (Headley and Hoy, 1987).
◦ However, the development of recombinant DNA techniques has made
it possible or at least conceivable to transfer genes specifying
beneficial traits directly to arthropods (Ashburner et al., 1998; Heilmann
et al., 1994; Hoy, 1994).

3. Advantages of use of genetic engineering methods for
the improvement of beneficial arthropods over artificial
selection
◦ The goal of genetic improvement can be achieved rapidly, without the
generations of rearing required for classical selection protocols
◦ Rather than selecting solely from the available gene pool of the
arthropod natural enemy, any gene from any species can be used, in
principle, for genetic improvement.

4. Predatory Mites and Parasitic Wasps
◦ An alternative gene delivery method,
maternal microinjection, was developed to
trans- form the pesticide resistance in western
predatory mite, Metaseiulus occidentalis
(Presnail and Hoy, 1992).
◦ Maternal microinjection of mites proved to be
easier than microinjection of mite eggs.
◦ Maternal microinjection was also attempted
with a braconid parasitoid wasp, Cardiochiles
diaphaniae (Presnail and Hoy, 1996).

6. GENETIC ENGINEERING OF INSECT PATHOGENS
◦ The ability to enhance the insecticidal properties of each group of
entomopathogens is related to the degree of understanding of the
biology of pathogenicity and the ease of genetic manipulation.
◦ Most progress has been made toward optimization of baculovirus
insecticides at the genetic level. The sequences of several baculovirus
genomes are now known (Ahrens et al., 1997; Ayres et al., 1994; Gomi
et al., 1999) and analysis of this information has greatly facilitated
understanding of the biology of baculovirus–host interaction.

7. Fungi
◦ The broad host range of some entomopathogenic fungi, such as
Beauveria bassiana and Metarhizium anisopliae, is an attractive
characteristic for insect pest control.
◦ The molecular and biochemical bases of pathogenicity of M.
anisopliae, which causes green muscardine disease, have been
particularly well studied (St. Leger, 1995; 1993).
◦ M. anisopliae normally takes from 5 to 10 days to kill a host
insect. In order to enhance insecticidal efficacy, additional
copies of the Pr1 gene, which encodes a subtilisin-like protease
involved in host cuticle penetration, were engineered into the
genome of M. anisopliae (St. Leger et al., 1996).

9. Nematodes
◦ H. bacteriophora was engineered to express C. elegans Hsp70A
to enhance tolerance of high temperatures (Hashmi et al., 1998).
◦ Engineering of entomopathogenic nematodes could potentially
be used to enhance pathogenicity, improve environmental
tolerance, and alter host range once the genetic bases for these
traits have been elucidated (Poinar, 1991).

10. Bacteria
◦ Newly discovered toxin groups such as the vegetative insecticidal proteins (VIPs)
from B. cereus (Estruch et al., 1996; Yu et al., 1997), and the Pht toxins from
Photorhabdus luminescens (Bowen et al., 1998) used to enhance the insecticidal
properties of transgenic plants and/or pathogens, according to the site of action of
each toxin.
◦ The pathogenicity and host range of Bt has been improved by using both
recombinant and non-recombinant means.
◦ For example, the plasmid complement of a Bt strain can be altered without use of
recombinant DNA methods: ICP genes can be transferred between strains by a
conjugation-like process.
◦ A strain with generally good insecticidal activity is identified, and a variant that has
lost plasmids with ICP genes or has ICP genes with relatively poor activity is used
for incorporation of plasmids with genes encoding highly insecticidal ICPs.

11. Viruses
◦ There are a variety of proteins and peptides such as insect
neurotoxins that act within the hemocoel that are not active
against an insect pest by ingestion or by topical application.
◦ Insect viruses such as baculoviruses provide a delivery system
for these toxins into the hemocoel of the insect, where they have
access to the site of action.
◦ Such toxins provide a second line of offense against the host
insect in addition to the virus itself. The only insect viruses that
have been engineered for enhanced insecticidal performance
are the baculoviruses.

12. Example:
◦ The gene coding for the polyhedral envelope protein was deleted from
AcMNPV and resulted in a six-fold increase in infectivity against first
instar, Trichoplusia ni, compared to the wild-type virus (Ignoffo et al.,
1995).
◦ Toxins derived from Bacillus thuringiensis have been expressed in the
baculovirus expression system, which provides a useful supply of toxin
for physio- logical studies (Martens et al., 1990, 1995; Merryweather et
al., 1990; Pang et al., 1992).