Monitoring Susceptibility of Western Bean Cutworm (Lepidoptera: Noctuidae) Field Populations to Bacillus thuringiensis Cry1F 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 2013­2014 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.

Assessing the ecological risks from the persistence and spread of feral populations of insect-resistant transgenic maize.

One source of potential harm from the cultivation of transgenic crops is their dispersal, persistence and spread in non-agricultural land. Ecological damage may result from such spread if the abundance of valued species is reduced. The ability of a plant to spread in non-agricultural habitats is called its invasiveness potential. The risks posed by the invasiveness potential of transgenic crops are assessed by comparing in agronomic field trials the phenotypes of the crops with the phenotypes of genetically similar non-transgenic crops known to have low invasiveness potential. If the transgenic and non-transgenic crops are similar in traits believed to control invasiveness potential, it may be concluded that the transgenic crop has low invasiveness potential and poses negligible ecological risk via persistence and spread in non-agricultural habitats. If the phenotype of the transgenic crop is outside the range of the non-transgenic comparators for the traits controlling invasiveness potential, or if the comparative approach is regarded as inadequate for reasons of risk perception or risk communication, experiments that simulate the dispersal of the crop into non-agricultural habitats may be necessary. We describe such an experiment for several commercial insect-resistant transgenic maize events in conditions similar to those found in maize-growing regions of Mexico. As expected from comparative risk assessments, the transgenic maize was found to behave similarly to non-transgenic maize and to be non-invasive. The value of this experiment in assessing and communicating the negligible ecological risk posed by the low invasiveness potential of insect-resistant transgenic maize in Mexico is discussed.

Three-year field monitoring of Cry1F, event DAS-01507-1, maize hybrids for nontarget arthropod effects.

Field studies were conducted over a 3-yr period to investigate the potential effects of cultivating transgenic maize hybrids containing a Cry1F insect-resistant protein on nontarget arthropod abundance. The narrow spectrum of activity of Cry1F against a subset of lepidopteran pest species would not suggest broad-spectrum effects on nontarget arthropods. However, because of the insecticidal nature of Bt proteins, an alternate hypothesis is that some nontargets may be affected by exposure to the protein. To examine this hypothesis at the field level, monitoring for nontarget organism abundance was initiated at four locations across the U.S. Corn Belt from 2004 through 2006. At each location, paired fields (approximately 0.8 ha each) of commercial Cry1F maize hybrids and isogenic nontransgenic control hybrids were planted. Sampling methods used to monitor nontarget organisms included visual surveillance, sticky cards, pitfall traps, and litterbags. Data were analyzed using multivariate analyses to look for a general community level response to the treatments. Analysis of variance was conducted on individual taxa to detect differences distinct from the primary community response. Community level analyses of the nontarget arthropod abundance showed no significant impact on community abundance when comparing Bt with non-Bt maize fields. Analyses of the individual taxa also showed no significant differences in abundance between Bt and non-Bt fields. Results of these studies confirm earlier laboratory testing and support the hypothesis that Cry1F maize does not produce adverse effects on nontarget arthropods occurring in maize fields.