The olfactory reaction of larvae and moths was investigated towards 18 oils (6 natural oils and 12 commercial chemical oils). Some of these oils such as peppermint and camphor (natural oils) and eugenol and camphene (commercial oils) were repellent to both larvae and moths. Other oils such as strawberry and d-limonene were attractive to both larvae and moths. Some of the repellent oils were, therefore, tested for their effect on certain biological aspects of the insects. Eugenol and peppermint oils, each at the 0.01% conc., caused a significant depression in the fecundity of moth and decreased the percentage of egg hatchability. Eugenol oil was much more effective than peppermint oil at 1%. Dried (leaves, fruits or seeds) powder of 14 different plants species were tested in different concentrations with talcum powder (carrier material) against egg deposition. The results indicated that dried powders of Allium cepa, Curcuma longa, Colocasia antiqurum, Ocimum basilicum. Dodonaea viscose and Thuja orientalis played a highly significant role in reducing egg deposition. The most impressive effect was displayed by powders of D. viscose and A. cepa, which caused the highest depression in egg deposition as well as in the emerging offsprings. Ethanolic extracts of 11 plants indicated that extracts of Pithuranthos tortosus and Iphiona scabra caused the maximum inhibition of egg hatchability, followed by C. longa, Citrullus colocynthia and T. orientalis. Ethanolic extracts of Schinus terebenthiflius (leaves) and I. scabra caused the highest depression in the deposited eggs, as they played a remarkable role as ovipositor deterrents. The majority of the plant extracts at 1% conc. could protect potato tubers at different intervals according to the calculated tuber damage index as follows: Iphiopna > Pithuranthos > Curcuma > Schinus (fruits) Thuja > Schinus (leaves) > Dodonaea > Citrullus.
Biochemical approaches have been adopted to increase the potency of Bacillus thuringiensis var. entomocidus against the cotton leafworm Spodoptera littoralis. Chemicals of various groups were assessed with respect to their effect in increasing the potency of the endotoxin. Results indicate that some lipid emulsifying agents, protein solubilizing agents, and some of the non‐toxic nitrogenous compounds tested increased the potency of the endotoxin in varying degrees (2.7–21.7 fold increase). Sodium benzoate as a representative of aromatic compounds also enhanced the endotoxin potency (2.5 fold increase), while the chelating agent EDTA had an antagonistic effect. Calcium, zinc, and copper salts remarkably potentiated the effectiveness of the endotoxin; the factors of increase were 24 and 19 as shown with zinc sulphate and calcium oxide salts. In the light of the results obtained, the mode of action of these chemicals has been discussed. So, B. thuringiensis may perform with high potency at lower concentrations if it is combined with some of these active and low cost chemicals and thus adding to the feasibilities of use.
Zusammenfassung
Möglichkeiten zur Steigerung der Wirkung von Bacillus thuringiensis Berl. gegenüber Spodoptera littoralis (Boisd.) mit Hilfe einiger Chemikalien
Es wurden biochemische Versuche unternommen, um die Wirkung von B. thuringiensis var. entomocidus gegen die Raupen der Baumwolleule, S. littoralis, zu erhöhen. Dabei wurden chemische Verbindungen verschiedener Gruppen im Hinblick auf eine Steigerung der Endotoxin‐Wirkung betrachtet. Die Ergebnisse zeigen, daß einige Fett‐emulgierende und Protein‐lösende Substanzen sowie einige nicht‐giftige Stickstoffverbindungen die Endotoxin‐Wirkung in verschiedenem Maße (2,7‐21,7fache Steigerung) erhöhten. Auch Natriumbenzoat als eine repräsentative aromatische Verbindung führte zur Wirkungssteigerung (2,5fach). Dagegen zeigte der Chelatbildner EDTA einen antagonistischen Effekt. Kalzium‐, Zink‐ und Kupfersalze vergrößerten die Wirksamkeit des Endotoxins erheblich (Zinksulfat 24fach, Kalziumoxyd 19fach). Im Lichte dieser Ergebnisse wird der Wirkungsmechanismus der getesteten Chemikalien erörtert. Demnach könnte B. thuringiensis bei niedrigerer Konzentration eine höhere Wirkung erlangen, wenn es mit einem dieser aktiven, billigen und unschädlichen chemischen Verbindungen kombiniert wird.
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