Monitoring Susceptibility of Western Bean Cutworm (Lepidoptera: Noctuidae) Field Populations toBacillus thuringiensisCry1F Protein

Zea mays L. (maize) hybrids producing the Cry1F protein from Bacillus thuringiensis were first commercialized in the United States in 2003. These products demonstrated varying levels of moderate control, but not immunity to Striacosta albicosta (Smith) (Lepidoptera: Noctuidae) (western bean cutworm). Susceptibility of western bean cutworm to Cry1F protein was assessed in field populations collected in the mid- and western United States in 2003, 2004, 2013, and 2014 using diet bioassay. A meta-analysis of 32 western bean cutworm field collections assessed for susceptibility to Cry1F was conducted to investigate changes in susceptibility over time. Based on meta-analysis results, these data suggest a 5.2-fold increase in median lethal concentration (LC50) response to Cry1F in the 2013–2014 populations compared with collections that were assessed 10 yr earlier. Widespread use of Cry1F-producing maize hybrids over the past 10 yr may have contributed to favoring western bean cutworm populations with tolerance to the Cry1F protein.