The effect of Streptomyces lavendulae (Streptomycetaceae) culture filtrate (containing 1x104 CFU/ml) on Spondoptera littoralis larvae was studied in laboratory experiments. The thin-film technique was employed. Third instar larvae were exposed to different concentrations (226 CFU/cm2, 113 CFU/cm2, 56.5CFU/cm2 and 28.25CFU/cm2) for 24h. The LC50 was found to be 151.4 CFU/cm2 (95% F. L. = 122.7 CFU/cm2 - 201.3 CFU/cm2; Slope = 2.072 ± 0.089), obtained 7days post-treatment. The effects of S. lavendulae filtrate on survival, growth, pupation and emergence rates were investigated. Symptoms of exposure included: delay of pupation, formation of intermediate forms (larval-pupal and pupal-adult intermediates) and deformation of wings and mouth parts of the emerged adults. At a concentration of 226 CFU/ cm2, the cumulative larval mortality was 82.8%, while the percentage of adult moth emergence was reduced by 89.7%. Deleterious histological effects were observed in the mid-gut of the treated larvae five days post-treatment. Some epithelial cells showed histolysis and cytoplasmic vacuolation. The muscle fibers in the treated individuals were separated from each other. In the meantime, S. lavendulae culture filtrate caused a noticeable decrease in the proteins content especially in the cytoplasm of the larval mid-gut cells.
Key words: Toxicity, Streptomyces lavendulae, Histopathology, Protein, Spodoptera littoralis, Lepidoptera and Noctuidae
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