Effects of Bt Expression on Bollworm Distribution in the Cotton Canopy

There are numerous documented cases of cotton bollworm developing resistance to Bt in the field. Different parts of Bt cotton plants express different doses of Bt proteins, which may affect the decision-making process of bollworms when they select feeding sites. Bollworms can choose to avoid Bt and may have a higher rate of survival on plant parts with lower Bt expression. Typically, a supplemental application of insecticide is applied when Bt fails to adequately control a bollworm population. However, some resistant larvae may be able to avoid the insecticide treatment if they are located lower in the canopy in a structure that provides them with more protection from the spray. In this study, a split-plot design was replicated four times with 8 row plots containing four row sub-plots. The plots contained either non-Bt, Widestrike, or Bollgard II cotton. The plots were further divided into either untreated or insecticide treated sub-plots. Plants were selected from each sub-plot and each plant was entirely mapped for the presence of larvae and damage. This may aid in determining how different Bt technologies affect the feeding tendencies and distribution of bollworms in the cotton canopy. The data presented in this presentation is only from the first preliminary trial using this method. There are plans to perform more trials using the same methods in multiple locations in the next growing season of 2019.