Soon after the initial study was published by Iowa State University's Aaron Gassmann (Field-evolved Resistance to Bt Maize by Western Corn Rootworm, in the online journal PloS ONE), Monsanto offered this response:

http://www.monsanto.com/newsviews/Pages/gassmann-research-reminder-of-need-for-comprehensive-IPM.aspx

The study by Gassmann reports western corn rootworm in four fields in Iowa have developed resistance to the single Bt protein Cry3Bb1, which is used in Monsanto YieldGard VT Triple and Genuity VT Triple PRO corn products.

“We take performance and efficacy of our products seriously, and we are collaborating with Dr. Gassmann to better understand his initial data and to determine if and how they impact our IPM recommendations to growers,” according to Monsanto’s written response. “It appears he has demonstrated a difference in survival in the lab, but it is too early to tell whether there are implications for growers in the field.”

“Since launching a product with this trait in 2003, we have monitored and studied a consistently low incidence of performance issues in limited areas with high WCR densities and under specific environmental conditions. There has been no measurable increase in the frequency of these performance issues over time. Ongoing studies with Dr. Gassmann and others are critical to understanding the factors that lead to these performance challenges.”