Bt corn registrants are required to submit annual resistance monitoring reports for the following lepidopteran target pests:

• European corn borer (ECB);
• corn earworm (CEW); and
• southwestern corn borer (SWCB).

These reports have generally addressed two objectives:

• bioassay results of pest populations sampled from random locations in the Corn Belt; and
• the results of investigations into unexpected pest damage to Bt corn fields. 

The table in the file below lists the resistance monitoring reports received by EPA. Individual studies are generally identified by MRID numbers, though not all reports have assigned MRID numbers. 

• Bt Corn (Lepidoptera) Resistance Monitoring Studies (PDF)(7 pp, 57 K)