ABSTRACT
The efficacy of three Bacillus thuringiensis formulations, Agerin, Dipel 2X and Dipel DF were tested against 2nd larval instar of Spodoptera littoralis. The three formulations were tested in the laboratory, field and semi field experiments. The 48 hour LC50 for Agerin, Dipel 2X and Dipel DF were 0.18, 0.07 and 0.10 % for the three formulations, respectively. The results of the field experiment indicated that the general mean of reduction were 59.0, 55.9 and 58.6 % for the three Bt formulations (Agerin, Dipel 2X and Dipel DF, respectively). In addition, the general mean of mortality rate in the semi-field experiments were 60.3, 60.4 and 61.3 % for Agerin, Dipel 2X and Dipel DF, respectively. Moreover, the histopathological studies using ultrastructure microscopy were carried out on the midgut of 4th larval instar after the treatment of the second instars with LC50 of the three formulations. Ultrastructural observations of the midgut exposed to Agerin, Dipel 2X and Dipel DF showed similar results. Microvilli were irregular and broken, mitochondria degenerated, various sizes of round granules found in the cytoplasm . The cytoplasm filled with various sizes of vacuoles and Bt. these results confirm the opinion stated that the toxicities of the different three formulations, are similar to each other. Therefore the Egyptian Bacillus thuringiensis strain (Agerin) can be used for control of S. littoralis as it is cheap and readily available.
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