Janet J. Knodel, NDSU Department of Plant Pathology
Joel Ransom, NDSU Department of Plant Science
Northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, and western corn rootworm (WCR), D. virgifera virgifera LeConte, are major insect pests of corn in the Midwest. Corn rootworm (CRW) larvae damage plants by feeding on roots, which results in plant lodging and reduced yields. Many corn producers have adopted the strategy of planting hybrids expressing Bt (Bacillus thuringiensis) endotoxins to manage corn rootworms. Rootworm Bt-corn hybrids express Bt proteins that are specifically toxic to corn rootworm larvae. Western corn rootworm resistance to transgenic corn expressing Bt endotoxins has been confirmed in some states; however, the status of sensitivity to this technology has not been previously investigated in North Dakota corn rootworm populations.
Objective 1: This objective is to determine the geographic distribution, density, and species composition of corn rootworm species in southeastern North Dakota.
- In 2015, 19 fields in 12 North Dakota counties were monitored for corn rootworm beetle activity by using sticky traps.
- A total of 1,404 NCR and only 5 WCR were captured in 2015. Western corn rootworm populations declined significantly from 2013 when a total of 3,545 WCRs were captured; this is probably due to overwintering mortality from the open, cold winters of 2013-14 and 2014-15.
- Northern corn rootworm was the most common and had the highest density of the Diabrotica species in North Dakota.
Objective 2: The second objective is to determine if Bt resistance exists in North Dakota corn rootworm populations.
- Screened WCR and NCR for potential resistance to Cry3Bb1 and pyramided (Cry3Bb1 + Cry34/35Ab1) Bt corn endotoxins during the summer of 2015.
- WCR and NCR adults were field-collected from one problem field (>5 years of continuous corn with same Cry3Bb1 trait) near Arthur in Cass County during 2014.
- Controls for the experiment were obtained from WCR and NCR laboratory colonies at the USDA ARS laboratory in Brookings, SD that had never been exposed to any Bt endotoxins.
- Bioassays on WCR found significantly greater survival of the field population on Cry3Bb1 than laboratory (control) colony progeny, but not on the pyramided Bt endotoxins.
- For NCR, there were no significant differences in sensitivity to any of the Bt endotoxins between a susceptible laboratory colony and the field population of NCR; however, the bioassay used was developed for WCR and this study needs to be repeated with modifications.
- The lowest larval survival was observed in the pyramided Bt corn for both WCR (16% larval survival) and NCR (10% larval survival) from ND field-collected populations.
Objective 3: The following extension fact sheets will be developed and completed in the Spring Semester 2016:
- Corn Rootworm IPM in ND
- E1300, Corn Insects of North Dakota Affecting the Crop after Emergence
- E631, Corn Insects of ND Affecting Planting Decisions.