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Biocontrol Potential Of Bacillus Thuringiensis Isolated From Soil Samples Against Larva Of Mosquito
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GENERAL CHARACTERISTICS OF BACILLUS THURINGLENSIS
Bacillus
thuringiensis is a member of the genes Bacillus and like the other
members of the taxon, has the ability to form endospores that are
resistant to inactivation by heat, desiccation and organic solvent. The
spore formation of the organism varies from terminal to subterminal in
sporangia that are not swollen, therefore, Bacillus thuringiensis
resembles other members of Bacillus species in morphology and shape
(Stahly, Andrews, & Yousten, 1991). The organism is gram-positive
and facultitative anaerobes. The shape of the cells of the organism is
rod. The size when grown in standard liquid media varies 3 – 5um.
The
most distinguishing features of Bacillus thuringiensis from other
closely related Bacillus species. (eg Bacillus anthracis, Bacillus.
cereus) is the presence of the parasporal crystal body that is near to
the spore outside the exosporangium during the endospore formation,
which is shown in figure 1:1 (Andrews, Bibilops, & Bulla, 1985;
Andrews, Faust, Wabiko, Raymond, & Bulla, 1987; Bulla, Faust,
Andrews, & Goodma, 1995). Bacillus thuringiensis is an insecticide
producing variant of Bacillus cereus (Gordon, Haynes, & Pang, 1973)
several Bt species also produce Bacillus cereus type enterotooxin
(Carlson, & Kolsto, 1993) plasmids coding for the insecticidal toxin
of Bacillus thuringiensis have been transferred into B. cereus to make
it a crystal producing variant of Bacillus thuringiensis(Gonzalez,
Brown, Carlton, 1982) molecular methods including genomic restriction
digestion analysis and 16 rRNA sequence comparison support that Bacillus
thuringiensis, Bacillus anthracis and Bacillus cereus are closely
relocated species and they should be considered as a single species
(Carlson, Caugant, & Kolstra, 1994; Ash , Farrow, Dorsch,
Stackebrandt, & Collins. 1991; Helgason et al.2000).
CLASSIFICATION OF BACILLUS THURINGIENSIS SUBSPECIES
The
classification of Bacillus thuringiensis based on the serological
analysis of the flagella antigens was introduced in the early 1960s (de
Barjac & Bonnefoi, 1962). This classification by serotype has been
supplemented by morphological and biochemical criteria (de Barjac,
1981). Clutill (1977), explains that only 13 Bacillus thuringiensis
subspecies were toxic to lepidopteran Larva only. And apparently
Nematode (Narva et; al., 1991) enlarged the host range and markedly
increased the number of subspecies up to the end of 1998, over 67
subspecies based on flagella H – Serovars had been identified.
ECOLOGY AND PREVALENCE OF BACILLUS THURINGRENSIS
Although
our knowledge about Bacillus thuringiensis occurs naturally and it can
also be added to an ecosystem artificially to control pest, prevalence
of Bacillus thuringiensis in nature can be said as “natural†and can be
isolated when there is no previous record of application of the organism
for pest control.
The Bacillus thuringiensis which belong to
artificial habitat areas are sprayed based insecticides (mixture of
spores and crystal). (Stahly et al. 1991). Thus, it is obvious that
Bacillus thuringiensis is widespread in nature. However, the normal
habitat of the organism is soil. The organism grows naturally as
asaprophyle, feeding on dead. Organic matter, therefore, the spores of
Bacillus thuringiensis persist in soil and its vegetative growth occurs
when there is nutrient available. Moreover Bacillus thuringiensis has
recently been isolated from marine environments (Maeda et al. 2000) and
from soil of Antarctica also (Foresty & Logan 2000).
However the
true role of the bacteria is not clear. Although it produces parasporal
crystal inclusions that are toxic to many orders of insects, some
species of Bacillus thuringiensis from diverse environments show no
insecticidal activity. The insecticidal activities of Bacillus
thuringiensis are rare in nature. For example, Iriarte et al.(2000)
reported that there is no relationship between mosquito breeding sites
and pathogenic action level of Bacillus thuringiensis in the surveyed
aquatic habitats. While another study suggested that habitat
with a high density of insect were originated by the pathogenic action
of this bacterium (Itoqou Apoyolo et al.1995).
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ABSRACT - [ Total Page(s): 1 ]A major challenge for achieving successful mosquito control is overcoming insecticide resistance. Bacillus thuringiensis which is one of the most effective biolarvacide for control of species of mosquitoes and monitoring of larval susceptibility is essential to avoid resistance development. Mosquito larvacidal activity of Bacillus thuringiensis was assessed by isolating them from ecologically different soil habitats in and around Enugu metropolis. The isolate organisms were confirmed as Bacillus ... Continue reading---
