Abstract
The toxic effect of four different compounds, namely protecto (bioinsecticide based on Bacillus thuringienses), coumarin (plant extract of Chicory flower), Neemix (plant extract of Azadirachta indica) and lannate (chemical insecticide) against the fourth instars larvae of cotton leafworm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) by LC50 concentrations were evaluated under laboratory conditions. Methomyl led to basement and peritrophic membrane detachment and destruction, appearance of numerous vacuoles, destruction of epithelial cells that emptied their cytoplasmic contents in the lumen, while protecto caused detachment and destruction of the basement and peritrophic membrane, vacuolization and destruction of the epithelial cells. Plant extracts (coumarin and azadirachtin) caused basement membrane detachment followed by destruction, destruction of epithelial cells which showed thickness in some points, in some cases the epithelial cells appeared deformed and become elongate in size than those of the control. The tested compounds caused significant decrease in the total soluble protein content of the 4th instar larvae. All compounds (except methomyl) caused significant increase in the activity of acetylcholinesterase enzyme and caused significant increase in the activity of acid phosphatase and amylase enzyme (except protecto and methomyl decrease the activity of amylase enzyme), on contrary, tested compounds showed significant decrease in the activity of alkaline phosphatase enzyme, coumarin and azadirachtin significantly increased α-esterase, while the other compounds caused significant decrease in the activity of this enzyme and β-esterase enzyme. Also tested compounds expect methomyl caused significant inhibition in the activity of GOT, on contrary, all tested compounds except coumarin caused significant decrease in the activity of GPT and invertase activity. Trehalase showed the same decreasing effects (except coumarin), while azadirachtin similar to control and had no effect.
Key word: Biochemical, histological, plant extracts, methomyl, bio-insecticide, cotton leafworm, Spodoptera littoralis (Boisd.) |
