Scope of Genetic Engineered Microbes and Parasitoids in Biological Control
- 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).