Location: Plant Genetics Research2013 Annual Report
1a. Objectives (from AD-416):
Characterize interactions of western corn rootworm with transgenic corn expressing RNAi that is toxic to rootworm.
1b. Approach (from AD-416):
Within the overall objective, there are three primary approaches: 1) Evaluate the role of feeding behavior in resistance of neonate western corn rootworm larvae resistant to Cry3Bb1-expressing transgenic maize by quantifying time to first feeding, total feeding time, total searching time, number of feeding episodes and their average duration, total number of bites during search behavior (a unique behavior observed in other trials), and total number and duration of a “still” behavior. 2) Work with Cooperator to quantify Cry3Bb1 protein and RNAi levels in the midguts of Cry3Bb1-selected, and its paired unselected WCR colonies after feeding on MON88017, RNAi, Cry3Bb1×RNAi, and their isoline in the laboratory, and 3) conduct a field experiment with Cry3Bb1 corn to test whether or not the same number of western corn rootworm eggs hatching over an extended time cause more damage to Cry3Bb1 transgenic corn than eggs hatching over a shorter period of time. This is to test a "martyr" hypothesis that early hatching larvae open paths to parts of the root with lower levels of Cry3Bb1, so that later hatching larvae would do better. Approach 3 tests this hypothesis in the field.
3. Progress Report:
The current project is related to parent project sub-objective 1.B “Evaluate our mCry3A-resistant colony for the heredity of this trait, whether the trait is maintained when selection is removed, and whether there are fitness costs associated with the trait” and sub-objective 1.C. “Evaluate cross resistance in rootworm colonies selected for resistance to one rootworm product on other single and stacked trait products.” It also contributes to Component 2A 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 with resistance to corn rootworm larval feeding has been an effective option for rootworm management since it became available in 2003. Unfortunately, resistance has developed in the field to at least the original Bt product. A series of experiments were conducted by ARS scientists in Columbia, MO aimed at understanding rootworm feeding behavior on Bt corn as a potential mechanism of resistance. To this point, available evidence does not point toward feeding behavior as playing a major role in the development of resistance of the western corn rootworm to Bt corn. Data are important to seed companies and modelers attempting to optimize resistance management plans for transgenic corn required by the Environmental Protection Agency for commercialization.