الفهرس 
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Abstract
Cotton bollworm (American bollworm, Helicoverpa armigera (Hub.), spiny bollworm Earias insulana (Boisd) and pink bollworm, Pectinophora gossypiella (Saund.) are important pests of cotton. Insecticide activity as microbial insecticide offers numerous advantages over chemical control agents. These insecticide crystal proteins are species – specific, and that make it harmless to non- target organisms and to the environment. A control program based on selective materials, which would allow survival of beneficial species and cause the mortality of destructive ones, is desirable. There fore, isolation of the pathogens from the native ecosystem well help in successful biological control program. The present experiments were conducted in El-Dakhlia Governorate, Aga district, throughout two successive cotton seasons of 2006 and 2007. One feddan had been selected to isolate and identify the local strains of entomopathgenic bacteria which associated with the American (H. armigera), spiny (E. insulana) and pink (P. gossypiella) bollworm larvae on cotton Giza 86. I. Laboratory Experiments : . Pathogenicity of bacterial isolates to ABW, SBW and PBW larvae: 1 The percentages of infected ABW larvae caused by B. thurigiensis (strain I, II and III), Streptomyces avermecti and Micrococcus sp. reached 90.0±6.8, 78.0±5.5 and 80.0±6.8, 76.0±7.2 and 60.0±8.6%, respectively, while the control experiment (distilled water) had 4.0±2.5%. Statistical analysis indicated that B. thurigiensis (strain I) had the highest pathogenicity to American bollworm, while B. thuringeinsis (strain II and III) and S. avermecti ranked second in the order of activity. Micrococcus sp. was the lowest entomopathogenic bacterium.2) The percentages of infected SBW larvae caused by B. thurigiensis (strain I, II and III), S. avermecti and Micrococcus sp. reached 100±0.0 ,288.0±7.8 and 82.0±4.5, 74.0±6.9 and 70.6±11.4%, respectively, while the control experiment (distilled water) had no infection. Statistical analysis indicated that B. thurigiensis had the highest pathogenicity to SBW. While, the percentages of infection caused by S. avermecti and Micrococcus sp. ranked second in the order of activity with no significant differences between them.3) The percentages of infected PBW larvae caused by B. thurigiensis (strain I, II and III), S. avermecti and Micrococcus sp. reached 96.0±5.8, 80.4±7.9, 84.0±10.1, 78.1±12.1 and 66.1±7.9%, respectively, while the control experiment (distilled water) had 2.0±2.2%. Statistical analysis indicated that strain I of B. thurigiensis had the highest pathogenicity to PBW, while B. thuringeinsis (strain 2 and 3) and S. avermecti ranked second in the order of activity. Micrococcus sp. was the lowest entomopathogenic bacterium. 2. Influence of B. thuringeinsis (strain I) and S. avermecti on the metamorphoses of E. insulana and P. gossypiella treated as first instar larvae. When the newly hatched PBW larvae treated with the B. thuringiensis strain I (at concentrations 1.0x106 cells/ml) completely inhibited the larval development. While, at the same concentration (1.0x106 cells/ml) of S. avermecti 97.2% of the treated larvae were inhibited. In respect to pupale stage, the inhibition of the pupal development was 50.8±10.8 and 33.6±5.2% at the concentration 5.0x105 cells/ml of B. thuringiensis strain I and S. avermecti. At the lowest concentration (2.5x105 cells/ml) the inhibition of the pupal development was 32.0±5.5 and 20.0±6.4%. When the newly hatched SBW larvae treated with B. thuringeinsis (strain I) and S. avermecti at concentration (1.0x106 cells/ml) completely inhibited the larval development. At the lowest concentration (2.5x105 cells/ml) 81.6±4.9 and 60.8±7.3% of treated larvae were inhibited in the cause of B. thuringeinsis starin I and S. avermecti. In respect to pupal stage, the inhibition of the pupale development was (56.2±9.8 & 47.6±9.2) and (53.2±12.2 & 32.6±10.5 %) at the concentration (5.0x105 and 2.5 X105 cells/ml) in case of B. thuringeinsis and S. avermecti, respectively. 3. Influence of B. thuringeinsis (strain I) on sex pheromone secretion by H. armigera and E. insulana: The obtained results exhibited gross differences in pheromone production between treated and untreated females (as larval stage) with B.t. strain I. Extraction of H. armigera and E. insulana virgin females treated with inoculum had no attractiveness to their males only 28.0±22.8 and 24.0±16.7% of tested H. armigera and E. insulana males showed positive response. On the contrary, significant high percentage (72.0±16.0 and 80.0±20.0%) of tested H. armigera and E. insulana males were attracted to pheromone extract of untreated virgin females. 1. The entomopathogenic bacteria, Bacillus thurengeinsis (strain I) promises to be a good biological control agent against cotton bollworms. 2. Control – B.T. application may be a useful control agent in early season where bacterial compound has no effect on the predator populations. 3. Pathogenic bacteria exhibited negative response to the increase of temperature and relative humidity. So, control – B.T. application may be a useful control agent when used at the right weather conditions. 4. Bacillus thurengeinsis (strain I) inhibited sex pheromone release in sex pheromone glands of Helicoverpa armigera (Hub.) and Earias insulana (Boisd) females.