The 3rd larval instar of the cotton leaf worm Spodoptera littoralis (Boisd.) were exposed (thin-film method) to a range of concentrations of two new synthetic pyrazolone compounds, 5-aminopyrazolo-pyrazolone and 3-pyrazolo-acrylate. The LC50 of 5-aminopyrazolo-pyrazolone was found to be 119.93 ppm for the tested species after three days of treatment, while it was 797.28 ppm for the 3-pyrazolo-acrylate after five days of treatment. The 5-aminopyrazolo-pyrazolone caused arrest or/and disruption of metamorphosis. Such metamorphic disruption induced a non-viable larva-pupa intermediates that died within 24 h. The 5-aminopyrazolo-pyrazolone was found to be more potent than the 3-pyrazolo-acrylate. The compound 5-aminopyrazolo-pyrazolone elicited deleterious histological alterations in the mid-gut of the treated larvae. At concentration of 1000ppm, the muscle layers were found to be much thicker than that of the control. Few epithelial cells were suffered from cytoplasmic vacuolization. Other cells exhibited an ill-defined plasma membrane, which lost their nuclei or appeared pyknotic. Shrinkage of the epithelial layer cells was observed after treatment. In the meantime, this compound caused increase in the total protein content (as demonstrated by the bromophenol blue method) in the larval mid-gut. Using gel electrophoresis technique, the compound 5-aminopyrazolo-pyrazolone decreased the intensity of DNA (after 3 days of treatment) and induced DNA fragmentation. The intensity of DNA fragments at 200 bp increased in the tissues of the treated S. littoralis larvae than in the control, in a dose dependant manner. The optical densities of the fragmented DNA at 200bp were 38 and 18 at concentrations of 1000 ppm and 50 ppm, respectively. The 5- aminopyrazolo-pyrazolone can be used in the control programs of S. littoralis.
Key words: pyrazolone compounds, DNA fragmentation, Apoptosis, Protein, Toxicity, Histopathology, Lepidoptera, Noctuidae and Spodoptera littoralis.
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