چكيده لاتين :
European Corn Borer Ostrinia nubilalis Hub. Sub sp. Persica (Lep.: Pyralidae) is known as a polyphagous insect, cause injury to corn, cotton, rice, poplar nursery and etc. Products of Bacillus thuringiensis, strains Kurstaki and Thuringiensis were evaluated on the host larval instars using spores and crystals. Bioassay was carried out the first larval star of the pest reared on different concentrations of strains added to the artificial diet. Seventy two hours after rearing, dead larvae were counted and lethal concentration to get 50 percent mortality in population (Lc50) was determined and compared with commercial product, Dipel®. Results
indicated that 13. thuringiensis var. Kurstaki (Lc50= 420.2 ppm) like Dipel (Lc50= 414.2 ppm) were more effective than B. thuringiensis var. Thuringiensis (Lc50 = 3892.72 ppm).
The second bioassay was done to determine the effective time to get lethal dose of B. thuringiensis by second larval instar of the host which reared on artificial diet, containing 2000 ppm of spores and crystals of Kurstaki strain. The mortality rate was estimated 17.2%, 50% and 82% after 2, 10.8 and 72 hours, respectively.
The third bioassay was carried out to verify susceptibility of larval stages when they reared on 500 ppm of B. thuringiensis var. Kurstaki. Results indicated that the first larval instar was significantly more susceptible than third instar. The fifth instar was less susceptible compare to other instars at (a=5%).
