Microbial Control on Sesamia cretica Insects by Beauveria bassiana at Sharkia Governorate

This research was performed in Sharkia
Governorate during seasons of 2014and 2015 under laboratory conditions. Beauveria
bassiana (Blas.) is an imperfect entomopathogenic fungus that attacks a
wide range of agriculture pests causing disease named as white muscardine and currently used as biocontrol agents and
substitute the harmful chemical insecticides. Beauveria bassiana isolate
(Cairo MIRCEN) was evaluated as biocontrol agent against Sesamia cretica
Led. under laboratory conditions. B. bassiana caused 100% mortality
to S. cretica after 5 days. B.
bassiana was screened for lytic enzyme production as it had the ability to
produce chitinase, protease and no lipase production. Environmental and
nutritional conditions were studied to detect the optimum conditions for
growth, protease production. Fungal isolate
was identified by both microscopic conditions. Culture filtrate of B. bassiana 1572 become concentrated (partial purified
active compound by organic solvents
(chloroform)) and tested on insects Sesamia cretica (larva at different
ages) as bioinsecticide in comparison with diluted (original filtrate). Results
were indicated after microscopic examinations as a complete change in insect
body colour to be deep darker, Appearance of white growth of the fungal B.
bassiana 1572 on the treated dead insect body in both treatments and the
insect cadaver was solidified and there were some black lesions and some
malformation. All symptoms were more in concentrated treatment than the other
treatment.Also beauvericin toxin production was investigated by molecular
weight using SDS- Protein Electrophoresis that indicated the presence of
beauvericin toxin in both concentrated (partial purified active compound by organic solvents (chloroform)) and  diluted (original filtrate). When conidia of B.
bassiana 1572
became in contact with the insect cuticle surface under suitable ecological
condition, it germinate, by the aid of both chemical (lytic enzyme secretion
(chitinase, protease)) and mechanical effect (hyphal pressure on the
penetration site. Then, hyphae penetrate the insect body cavity. That led to
hyphae growth, division, beauvericin toxin production and production of spores
spreaded in the hemolymph (in all parts of body cavity), after that physical
and chemical changes occurred to the insect hemolymph by the aid of beauvericin
toxin led to function disorder and death. The fungus grew
outside the cadaver until the availability of suitable conditions to resume
life cycle.