Toxicity and biochemical impacts of spinosad on the Pink Corn Stem Borer Sesamia cretica Led. (Lepidoptera: Noctuidae)Abstract :
The toxicity of Spinosad to different larval instars of the pink corn stem borer, Sesamia cretica Led. (Lepidoptera: Noctuidae), was evaluated under laboratory and field conditions. The impact of Spinosad on the protein content and glycogen level of larvae was also taken into consideration. Data indicated that Spinosad had toxic activity against the tested larval instar and the mortality was in the order of first instar > second instar > third instar > fourth instar > fifth instar with respective LC50 values of 0.008, 0.016, 0.028, 0.044 and 0.159 ml/l after 7 days of treatment. Also, the field experiment showed high efficiency of Spinosad at the highest three concentrations down to 25% FR (0.125 m/l) against S. cretica larvae, which resulted in significant reduction in the number of plants containing either perforated stem or dead hearted case, number of larvae, tunnels and excavated areas inside infested plants. Regarding the biochemical parameters, results proved that the protein content and glycogen level in the treated larvae was significantly lower than that of the control at all concentrations of exposure. The highest rate of decreasing in total protein content was -54.5% for 2nd instar larvae exposed to 50% FR (0.25ml/l). Also, the decrease in glycogen level in the treated larvae was concentration-dependent and reached -55.8% to 2nd instar larvae exposure to 50% FR (0.25 ml/l.).
Spinosad, Sesamia cretica, toxicity, biochemical impacts, protein contents, glycogen level.