Abstract
Pyramiding (combining) of plant incorporated protectants (PIPs) with insecticidal activity in genetically engineered crops is a strategy used to improve efficacy as well as delay potential resistance for a specific group of targets. In some countries, a regulatory risk assessment is required for breeding “stacks” expressing multiple PIPs and these countries may require an assessment of potential interaction among the PIPs. This study evaluated whether combining soybean events MON 87551 and MON 87701 results in a toxicological interaction that effects a species that is controlled by each event. MON 87751 coexpresses the Cry1A.105 and Cry2Ab2 proteins and MON 87701 expresses the Cry1Ac protein. EC50 values for MON 87751 and MON 87701 were comparable in diet-incorporation bioassays using corn earworm (Lepidoptera: Noctuidae, Helicoverpa zea) and the observed combined activity of the stack was consistent with predictions of additivity (i.e., no interaction). Under the concentration and response addition models, predicted and observed median effect levels differed by <10%. These results demonstrate independent action at the median effect level between the insecticidal activity of MON 87751 and MON 87701. Taken together, no interaction between these PIPs and acceptable margins of safety for the individual proteins to nontarget organisms, it is appropriate to bridge back to the risk assessments for the individual products that demonstrated environmental safety of stack products containing both MON 87751 and MON 87701.
Highlights
Pyramiding of plant incorporated protectants (PIPs) with insecticidal activity in genetically engineered crops is a strategy used to improve efficacy as well as delay potential resistance for a specific group of targets
The predicted EC50 value under the response addition model of 1.1 μg tissue/ml diet is captured within the 95% confidence interval (CI) for the observed EC50 value for the stack (0.79 to 1.4 μg tissue/ml diet), demonstrating that the combined response to MON 87751 and MON 87701 is consistent with additivity (Table 3)
The results from bioassays with H. zea demonstrate that the combined activity of MON 87751 and MON 87701 is consistent with additivity
Summary
Pyramiding (combining) of plant incorporated protectants (PIPs) with insecticidal activity in genetically engineered crops is a strategy used to improve efficacy as well as delay potential resistance for a specific group of targets. The Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (FIFRA SAP) recommended to USEPA that for combinations of PIPs that have been previously registered as individual events and have a proven safety record, that GTA interaction less than 10-fold should not trigger additional NTO testing (USEPA 2009b). The rationale for this recommendation provides a risk-based approach to address GTA effects in the context of an environmental risk assessment. Several published Bt interaction studies have used the response addition model to effectively test the hypothesis of no-interaction (Raybould et al 2010, Levine et al 2015, Graser et al 2017)
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