الفهرس 
RESULTS AND DISCUSSIONOnly 14 pages are availabe for public view
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Abstract
A set of experiment were carried out to investigate and monitoring. The susceptibility and tolerance level of certain field strains of cotton leafworm Spodoptera littoralis to Dipel 2x and Agerin Bacillus thuringiensis microbial biocides. Certain biochemical parameters in treat larvae strains were also evaluated as a biomarker or bioindicator to differences in toxicity of these biocides to tested strains moreover the histopathological changes in the mid-gut of treated larvae due to treatment with these microbial biocides were evaluated to conform its biological activity.The obtained results could be summarized as following:
1- Susceptibility and tolerance level of some cotton Leafworm field strains to certain microbial biocides.
In generally, the efficacy of the commercial product Dipel2x (Bt subsp. kurstaki) was the most potent compound comparing with Agerin biocide based on LC50s values. On the other hand, results indicated that Assuit strain recorded the highest resistance level against Dipel2x and Agerin biocides compared with other field strains based on LC50s values .It could be concluded here that the two investigated biocides have good biological activity to the 2nd instar larvae of cotton leafworm Spodoptera littoralis field strains.
2- Effect of microbial biocides on the activity of certain enzymes of treated cotton leafworm larval strains:
2.1. Effect of Dipel 2x and Agerin on ATP-ase activity:
Results revealed that a significant different was found between laboratory and investigated field strains in specific activity of ATP-ase activity after treatment LC50 of Dipel 2x and Agerin biocides. Thus an activation of ATP-ase was recorded in laboratory strain and El- Menofia field strain. While an inhibition in this enzyme was occurred in other field strains. The activation of ATP-ase is more pronounced in laboratory strain which recorded high response to bacterial insecticides.
2.2. Effect of Dipel 2x and Agerin on glucose content:
Generally, treatment with Dipel 2x and Agerin biocide decreased the glucose content in laboratory strain than other investigated field strains.. Also, the rate of decrease was more pronounced Menofia strain than other field strains. Assuit strain recorded the lowest degree of decrease in glucose content than investigated field strain.
2.3. Effect of dipel 2x and Agerin on protease activity:
On othe hand, treatment with Dipel 2x and Agerin caused highly elevate effect on protease activity in both of laboratory and field strain. This increase was begin after 6hr of treatment. The rate of increase was highly evidence in El-Sharkia than laboratory strain.
3. Histopathological changes in the 2nd larval instar of Spodoptera S.
littoralis. mid-gut treated with Bacillus thuringiensis biocides.
The histopathological changes in the mid-gut of treated 2nd instar larvae of El-Menofia and Assuit strains comparing with changes in laboratory strain were determined after 7 days from treatment with Dipel 2x and Agerin at LC50ُُs. Plates of sections revealed the following results.
3.1. Histopathological changes in mid-gut of laboratory strain
Treatment with Dipel 2x showed a great destructive of muscular and regenerative cell, necrotic epithelium and detachment of the basement membrane and formation of large vacuoles. Agerin damaged.The circular and longitudine muscles of mid-gut these muscles were largely. Also vacuolation in the epithelium was observed.
3.2. Histopathological changes in mid-gut of El-Menofia strains
Generally, the changes in El-Menofia strain was similar or near to the changes in mid-gut of laboratory strain with both of tested biocides.
3.3. Histopathological changes in mid-gut of Assuit strains
Agerin was less effective than Dipel 2x , it showed a slight histological alterations of epithelial cells like elongation and fad in their boundaries .Additionally, a few scattered groups of epithelial cells were sloughed of in space between the epithelium and peritrophic membrane .It was also observed vacuolation in the epithelium.