Relative Injury level of Helicoverpa Armigera (HüBner) on Conventional and Transgenic Cotton Expressing Cry1Ac

During 2008-2009, there was no larval recovery as well as fruiting body damage at any level of infestation up to 135 DAS. However, at 151 DAS, larval recovery of 0.33 & 1 and fruiting body damage of 0.76 and 2.09% were recorded in treatments with 4 and 5 larvae released/plant, respectively. In the year 2009-2010, larval recovery of 0.33 was observed earlier at 135 DAS along with damage of 0.83 and 1.29% in treatments with 4 and 5 larvae released/plant, respectively. On contrary, significant fruiting body damage and the larval recovery was observed on non-Bt F1861. The EIL (Economic Injury Level) of H. armigera for non-Bt F1861 calculated using gain threshold and regression coefficient between the variables, population level of pest and yield worked out to be 0.52 larvae/plant. However, due to non significant larval recovery and yield damage in RCH 134 Bt cotton hybrid, the EIL was calculated to be 17.91-22.20 larvae/plant, did not have any biological significance. This was indicative of that the expression of cry toxin in RCH 134 Bt cotton hybrid was sufficient till 151 DAS to kill even five larvae of H. armigera released/plant and secondly, H. armigera population used in the studies was highly susceptible to Cry1Ac toxin expressed in Bt cotton.