How Resistance Could Develop in Corn Rootworm (CRW)
The level of understanding of resistance development in CRW is low compared with that of ECB, however many studies are underway. Several factors still need to be investigated. There are a few key differences between the two insects in their exposure to resistance selection. CRW have two life stages exposed to Bt; larva and adult. Also, the dose that CRW is exposed to is low to moderate for the CRW Bt events, as opposed to high dose in the ECB Bt events. Though CRW Bt corn hybrids are effective at protecting the roots from larval injury, some adult emergence will take place from these Bt fields. Another biological difference is that CRW mate in the same field as they emerge, reducing the chance of genetic mixing from nearby non Bt fields.
For these reasons, entomologists recommend a proactive approach to resistance management for the time being. The current requirement for refuge size and configuration for CRW Bt hybrids takes is similar to the ECB refuge requirement. However, the CRW refuge must be placed within or adjacent to the CRW Bt corn hybrid to accommodate the limited movement of CRW adults at mating.