Influence of Bt Transgenic Cotton on Larval Survival of Common Cutworm Spodoptera litura

Transgenic Bt cotton line GK12 was used to test the toxicity of Bt cotton leaves, flowers, buds and bolls to the nontarget pest, common cutworm Spodoptera litura (Fabricius), with its parental nonBt cotton line Simian3 as control. Survival rates on 2nd, 4th, 6th and 10th day of the newlyhatched larvae were measured when they were fed with above cotton organs of the two cotton lines respectively. Both cotton lines and cotton organs had significant influences on larval survival. But there was no interaction between cotton lines and cotton organs. Larval survival of S. litura didn't differ significantly within 10d when they fed on newlystretched cotton leaves (1st from the top) of either cotton line. Neither did on leaves in the middle part (3rd and 6th from the top) or on cotton buds of tested cotton lines. Feeding on matured cotton leaves (14th from the top) of GK12, larval survival was significantly lower than control from 4d to 10d. Feeding on cotton flowers, larval survival only differed within 4d between the two cotton lines. Larvae fed on cotton bolls had lower survival on GK12 than on its relative control, but the difference was not significant. Based on the comparison of toxicity of GK12 to S. litura and cotton bollworm Helicoverpa armigera, the possible cause of the increasing damage of S. litura in the Bt cotton fields was discussed.