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- Title
Toxicological Studies and Field Applications of a New Bacillus thuringiensis Isolate (Bt1) and Two Chemical Pesticides on Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae).
- Authors
Fifi, M. Reda; Hassanein, W. A.; Sherief, E. A. H.; Shahera, Moabed
- Abstract
A total of 35 bacterial cultures were isolated from dead and living larvae of cotton leafworm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) and soil samples. Only one bacterial isolate (Bt1) exhibited the highest pathogenicity against the pest. Identity of one of the most potent isolates suspected and encoded as Bt1 was confirmed by amplifying its 16S rRNA gene. Partial nucleotide sequence of the amplified 16S rRNA gene of the tested strain was submitted in GenBank with accession number KU646830. Pathogenicity of Bt1 strain was tested against 2nd and 4th instars of S. littoralis larvae at different concentrations (2x109, 2x108, 2x107 and 2x106CFU/ml). Based on the LC50 value, the 2nd instar larvae were more susceptible than the 4th one. It recorded 1.9x109CFU/ml and 4.1x1011CFU/ml for 2nd and 4th larval instars, respectively, after seven days. Latent effect of Bt1 strain was recorded on some S. littoralis biological aspects as pupation, pupal weight and adult emergency that decreased, in addition to some failure in pupation and emergence of deformed adults. In vivo, screening of Bt1 strain culture filtrates against 2nd and 4th larval instars of S. littoralis cleared that filtrate including protease had significant effects on larval mortality. Purified protease gave single homogenous band of 68 kDa by SDS- PAGE. Also, its optimum pH and temperature were 7.0 and 35oC, respectively, with wide pH and thermal stabilities. Furthermore, purified protease showed high activity against 2nd and 4th instars S. littoralis larvae than crude protease. A field application was conducted to compare the efficacy of the recommended pesticides (Challenger Super and New benzuron) and Bt1 culture against the 2nd and 4th instars S. littoralis larvae. Results showed that Challenger Super was the most effective insecticide and caused 89.61, 93.6 and 88.68% reduction in S. littoralis population after 3, 7 and 10 days post treatment, respectively. However, Bt1 strain was the least toxic effect where the mean reduction was 40.5%.
- Subjects
TOXICOLOGY of Bacillus thuringiensis; SPODOPTERA littoralis; NOCTUIDAE; VIRULENCE of bacteria; RIBOSOMAL RNA; NUCLEOTIDE sequence
- Publication
Egyptian Journal of Biological Pest Control, 2016, Vol 26, Issue 2, p229
- ISSN
1110-1768
- Publication type
Article