Contents - Faperta

Genetic Engineering of Entomopathogenic Microbes for Pest Management 275
mitotically stable on either selective or nonselective medium. Southern blot and hybridization
of undigested fungal DNA of wild type and four transformants, probed with
beta-tubulin sequence of pSV50, showed hybridization at the high Mr region of genomic
DNA in four transformants. Virulence tests of the transformants showed that there was no
signifi cant loss in the pathogenicity toward third-instar larvae of H. armigera.
The cry1Aa1 gene encoding insecticidal crystal protein (ICP) from the pES1 has been
cloned into E. coli plasmid vector pTZ19U to form pUN4 (Lin et al., 2002). The pUN4
was transferred into three isolates of epiphytic fungus, Erwinia herbicola (Löhnis) Dye by
electroporation. The transformed E. herbicola strains Eh4, Eh5, and Eh6 expressed the toxin
protein and conferred insecticidal activity. Protein extracts from the E. herbicola transformants
(2.5 mg mL 1 ) resulted in 94 to 100% mortality of diamondback moth, P. xylostella.
At 0.312 mg of protein extract mL 1 , Eh4 and Eh5 showed 26% and 42% mortality, respectively.
Eh4 or Eh5 resulted in up to 84% mortality after 48 hours at 1.25 mg protein extract
mL 1 . Insecticidal activity in the transformed E. herbicola strains makes it a good candidate
as an environmentally friendly biopesticide.
Entomopathogenic Protozoa
Protozoa play an important role in population regulation of insect pests (Maddox, 1987;
Brooks, 1988). They are host specifi c, slow acting, and produce chronic infections. They
develop in a living insect, and require an intermediate host. Microsporidia are the most
common protozoa infecting insects. They are persistent in nature, recycle, and affect reproduction
and overall fi tness of insects. Only a few species have been used in inundative
releases (Solter and Becnel, 2000). The grasshopper pathogen, Nosema locustae Canning has
been registered and used commercially (Henry and Oma, 1981). Their major drawback is
low level of mortality and the need to produce them on living hosts. Genetic engineering
can be used to overcome some of these drawbacks in the future.
Entomopathogenic Nematodes
Entomopathogenic nematodes of the genera Steinernema and Heterorhabditis have
emerged as excellent candidates for biological control of insect pests (Atkinson, 1993).
Entomopathogenic nematodes are associated with the bacterium, Xenorhabdus and are
quite effective against a wide range of soil-inhabiting insects. The relationship between
nematodes and the bacterium is symbiotic because the nematodes cannot reproduce inside
the insects without the bacterium, and the bacterium cannot enter the insect hemocoel
without the nematode and cause the infection (Poinar, 1990). Broad host range, high virulence,
safety to nontarget organisms, and their effectiveness under certain conditions have
made them ideal biological control agents. Liquid formulations and better application
strategies have allowed nematode-based products to be quite competitive for pest management
in high-value crops. Nematodes are generally more expensive to produce than insecticides,
and their effectiveness is limited to certain niches and insect species. There is a need
to improve culturing techniques, formulations, quality, and the application technology.