Synergistic Effect of Gamma Irradiation and Bacillus thuringiensis on the Black Cutworm, Agrotis ipsilon (HUFN.)1.

The main objective of the present laboratory investigation was designed to evaluate the integrated impact of commercial formulation Xentari 54% WP (Bacillus thuringiensis aizawai) and gamma radiation against 4^th instar larvae of Agrotis ipsilon. Full grown male pupae were irradiated with the sub-sterilizing dose 100Gy. The resulting 4^th instar larvae of first generation (F1) were exposed to four different concentrations (3x10⁴, 6x10⁴, 9x10⁴ and 12x10⁴ D.U./100ml). Also, the mortality percentage was recorded daily in unirradiated fourth instar larvae treated with the same Bt. concentrations. The accumulative daily mortality revealed that when concentrations and time increased, the mortality percentage increased as well. The LC₅₀ and LC₉₀ levels of irradiated and unirradiated A. ipsilun F1 4^th larval instars treated after 24 hours of feeding on leaves treated with various concentrations of Bt. (Xentari 54% WP) revealed that irradiated parents of A. ipsilon F1 4^th larval instar were more vulnerable to Bt. than unirradiated ones. Also, histological study was carried out to describe the histological changes of the midgut tissues F1 larvae due to influence of gamma radiation either alone or in combination with LC₅₀ of Bt. Results obtained revealed that large number of epithelial cells became vacuolated. The histopathological symptoms were severe which was clearly obvious by cells lysis and unclear of the epithelium nuclei. The combination of Bt. and gamma radiation may offer an acceptable integrated pest management program against A. ipsilon. [ABSTRACT FROM AUTHOR]