2012 Annual Report
1a.Objectives (from AD-416):
Develop colonies with resistance to Cry34/35Ab1 and test the effectiveness of two refuge types to delay resistance. Test the dominance and fitness costs of resistance to Bt corn.
1b.Approach (from AD-416):
Western corn rootworm colonies will be selected for resistance to Cry34/35Ab1-expressing transgenic maize and resistance levels will be compared to control colonies and colonies designed to simulate a refuge. In addition, dominance of resistance will be tested by crossing resistant and susceptible colonies and evaluating progeny and fitness costs associated with resistance will also be evaluated.
This work is related to sub-objective 1.A of the parent project: “Develop colonies with resistance to Cry34/35Ab1 and test the effectiveness of different refuge types to delay resistance” and contributes to Component IIa of the National Program 304 Action Plan by developing increased knowledge of the biology, ecology, behavior, and genetics of pests, and plant traits conferring pest resistance.
Transgenic corn is effective in rootworm management, but in order to maintain its effectiveness, “refuges” designed to delay resistance must be useful and well-designed. Understanding which “refuge” types of non-Bt corn are effective in delaying resistance can extend management options beyond that which would be otherwise possible. Colonies of the western corn rootworm aimed at evaluating “refuges” (planting of non-Bt corn) for delaying resistance to Cry34/35Ab1 transgenic corn) are in the sixth generation of selection in Ames, IA. The effect of selection schemes on resistance to Cry34/35Ab1 proteins targeting western corn rootworm management are being evaluated. In addition, two generations of backcrossing and one generation of selection have been completed for Cry3Bb1 resistant colonies and fitness costs measurements for this population have begun. Overall, these colonies provide an understanding to what extent the mandatory planting of non-Bt corn assists in the delay in the development of resistance to insecticidal transgenic corn targeted toward corn rootworms and whether or not fitness costs are associated with resistance.