Iowa has got Bt resistant corn rootworm.
But you don't have to worry. They not likely to spread to South Dakota, says Buyung Hadi, South Dakota State University entomologist. Most corn rootworms beetles don't move around a lot.
But a resistant population could develop in South Dakota on its own if you use the same Bt-trait over and over.
"The finding in Iowa serves as a reminder that continuous planting of the same Bt-corn variety increases the chance of pest resistance development against the Bt-trait associated with the variety," Hadi says. "Moreover, this finding illustrates the vulnerability of over-reliance on a single control method to manage crop pests. In the end, integration of multiple IPM components, such as variety or crop rotation and refuge compliance, is foundational to avoid the development of pest resistance and successfully manage a pest in long term."
A research paper published last July by a team of scientists from Iowa State University documented an incidence of resistance against Bt-corn on field collected western corn rootworms. The authors collected western corn rootworms from a number of fields that have been continuously planted with Bt-corn containing Cry3Bb1 trait for 3-5 years. The fields were identified by Iowan farmers reporting high rootworm injuries to the extension service.
Rootworms collected from these fields were designated as "problem field rootworms" and reared in a laboratory. In subsequent experiments, the researchers found that the progenies of have an increased survival rate when reared on Bt-corn with Cry3Bb1 trait compared to susceptible rootworm populations.
No increased survival rate was observed when the 'problem field rootworms' were reared on Bt-corn with Cry34/35Ab1 trait.
The Cry3Bb1 trait can be found on hybrids such as YieldGard Vt Rootworm or Genuity Triple Pro.
The Cry34/35Ab1 trait is found on hbyrids such as Herculex RW and Optimum AcreMax RW.
For a guide to Bt-corn traits, see