The US EPA has issued a proposal to improve the country’s current resistance management strategies for certain Lepidopteran pests of insect-resistant Bacillus thuringiensis (Bt) corn and cotton. The measures proposed are targeted at delaying lepidopteran development of resistance to Bt corn and cotton traits in response to multiple reports of Bt resistance among some pests.

Bt resistance has been reported for corn earworm (Helicoverpa zea), fall armyworm (Spodoptera frugiperda), western bean cutworm (Striacosta albicosta), and southwestern corn borer (Diatraea grandiosella). The EPA identified a number of risk factors that likely contributed to these resistance cases and could lead to more widespread resistance incidents in the future. These risk factors include a lack of “high dose” toxin expression in Bt traits for some of the Lepidopteran target pests, cross-resistance between different Bt traits, cross-pollination of Bt and refuge plants in Bt corn seed blend products, poor compliance with non-PIP (Plant-Incorporated Protectant) refuge requirements, and ineffective resistance monitoring methods.

To delay the development of Bt resistance among corn and cotton pests, the US EPA has proposed a variety of measures, including those listed below, which have been made available for public comment:

• Phase Down of Single Traits and Non-Functional Pyramids: a short term phase-out (3-year timeframe) of single trait corn products controlling Lepidopteran pests and a long-term phase-out (5-year timeframe) of compromised pyramid corn and cotton products
• Increasing Percent Refuge in Seed Blend Products: an increase from 5% refuge-in-a-bag in Bt corn pyramid products to 10% refuge nationwide
• Refuge Compliance Monitoring: mandatory registrant on-farm refuge compliance visits, measures for non-compliant growers, increased seed dealer record keeping