Toxic and sub toxic effects of Bacillus Thuringiensis svar. kurstaki Toward Ectomyelois Ceratoniae (Lepidoptera: Pyralidae).

Abstract

The objective of this study is to determining mainly, the toxicity of Bacillus thuringiensis svar. kurstaki (Bt) on the first larval instar of Ectomyelois ceratoniae and also to study its deferred effect on other biological parameters such as the development and reproduction of this pest. We paired the treated larvae, The concentrations used are: 0,25 g/L (250 ppm), 0,5 g/1L (500 ppm), 1 g/L (1000 ppm), 1,5 g/L (1500 ppm) and 2 g/L (2000 ppm) (6 pairs for each dose used), and placed 6 control pairs on separate Petri dishes to count the number of eggs laid. We then tallied the number of eggs that hatched after their incubation. For Bt svar. kurstaki, the variable being measured is the rate of larval mortality. The results showed that there was a strong and positive link between the doses used and the adjusted mortality of the larvae across a range of bioinsecticide exposure times, the five Bt svar. kurstaki concentrations used had generated a corrected mortality of E. ceratoniae first instar larvae which varied between a minimum of 50.78% and a maximum of 97.92%. Bacillus thuringiensis svar. kurstaki becomes more and more toxic each time the larvae were exposed to the biopesticide. Thus, the LC50 of Bt svar. kurstaki for E. ceratoniae larvae, calculated at the concentrations of 250, 500, 1000, 1500, 2000 ppm were inversely proportional to the different lethal times. On the other hand, the Bt treatment decreased female insects' reproductive rate and egg viability. Therefore, the BT had a negative influence on the growth and reproduction parameters of E. ceratoniae.