Location: Plant Genetics Research2013 Annual Report
1a. Objectives (from AD-416):
1) To determine if differences in behavior between Bt resistant and Bt susceptible western corn rootworm larvae exist. 2) To determine if there is behavioral resistance to Bt in corn by evaluating a “martyr” hypothesis.
1b. Approach (from AD-416):
Previous research has shown that larvae of the WCR tend to show a non-preference towards feeding on the roots of Bt plants. Root scans of Bt plants indicate that the Bt proteins tend to “clump” in the plant root and form greater concentrations near the root tips. It is possible that rootworm larvae are able to detect the presence of Bt protein in the roots and actively avoid feeding on areas of high concentration thus circumventing the insecticidal properties of the plant. If this is the case there should be some difference in the feeding behavior between susceptible and Bt resistant WCR larval feeding. We will be evaluating behavior of WCR larvae resistant and susceptible to Bt in response to differing corn traits. Another observation of possible behavioral resistance to Bt involved a “martyr” hypothesis. Previous workers observed larval feeding on Bt corn plants in which 99% of the first introduced larvae died within 2 days. Three days later researchers added more larvae to the plants at which point 8% of the larvae survived. Three days after that another group of larvae were placed on the plant at which point 21% survived. The larvae were reported as visiting the same feeding locations as previous larvae. Researchers theorized that the previous feeding caused by the dead larvae had opened up pathways past the higher Bt concentrations in the root and thus allowed the later larvae to avoid it. We will conduct a series of studies to evaluate this hypothesis.
3. Progress Report:
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 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. A ‘martyr’ hypothesis suggesting that early hatching western corn rootworm larvae create paths for later hatching larvae to survive Bt corn was tested in the laboratory, greenhouse, and field by University of Missouri and ARS scientists in Columbia, MO. None of the experiments supported the hypothesis, so this was rejected as a potential explanation for western corn rootworm damage to Bt corn. Some of the experiments were conducted with both resistant and susceptible western corn rootworm colonies and similar results were obtained for both. This suggests that resistance that has evolved to Bt corn was not based solely on feeding behavior. These data will be valuable to the Environmental Protection Agency and industry as resistance management plans are optimized for current and future sources of resistance.