Nontarget organism effects tests on eCry3.1Ab and their application to the ecological risk assessment for cultivation of Event 5307 maize

Impacts of Bt rice on non-target organisms assessed by the hazard quotient (HQ)

The potential risk of Bt (Bacillus thuringiensis) crops on non-target organisms (NTOs) has drawn a lot of public concerns. Despite a series of risk assessments of Bt crops on NTOs has been conducted, a quantitative approach which could support a precise judgment of their safety is required. In the present work, hazard quotient (HQ) was applied in the safety evaluation of three Bt rice events (Cry1Ab, Cry1C and Cry2Aa rice) on NTOs. Eight NTOs in different functional guilds associated with Bt rice were selected to conduct the tests. The results showed that the HQs of three Bt rice events for eight NTOs were all below the trigger value 1, while the HQ of Cry1Ab rice for one target pest Chilo suppressalis was three times higher than 1. Our results assured the reliability of the HQ and indicated that the three Bt rice events would pose no risks to the eight NTOs. Further testing of three Bt proteins on biological parameters of one NTO Nasonia virtipennis under no observed adverse effect concentration (NOAEC) confirmed the robustness of HQ assessment. We recommend that the HQ could be applied in tier-1 risk assessments of Bt crops on NTOs as a reference data standard, which would provide more clear and credible safety information of transgenic crops for the public and policy makers.

Advancing ecological risk assessment on genetically engineered breeding stacks with combined insect-resistance traits

To inform the ecological risk assessment (ERA) of a transgenic crop with multiple insecticidal traits combined by conventional breeding (breeding stack), a comparative field study is customarily conducted to compare transgenic protein concentrations in a breeding stack to those in corresponding component single events used in the breeding process. This study tests the hypothesis that transgenic protein expression will not significantly increase due to stacking, such that existing margins of exposure erode to unacceptable levels. Corroboration of this hypothesis allows for the use of existing non-target organism (NTO) effects tests results, where doses were based on the estimated environmental concentrations determined for a component single event. Results from over 20 studies comparing expression profiles of insecticidal proteins produced by commercial events in various combinations of conventionally-bred stacks were examined to evaluate applying previously determined no-observed-effect concentrations (NOECs) to stack ERAs. This paper presents a large number of tests corroborating the hypothesis of no significant increase in insecticidal protein expression due to combination by conventional breeding, and much of the variation in protein expression is likely attributed to genetic and environmental factors. All transgenic protein concentrations were well within conservative margins between exposure and corresponding NOEC. This work supports the conclusion that protein expression data generated for single events and the conservative manner for setting NTO effects test concentrations allows for the transportability of existing NOECs to the ERA of conventionally-bred stacks, and that future tests of the stated hypothesis are no longer critically informative for ERA on breeding stacks.

Meeting technical challenges for protein characterization and surrogate equivalence studies that resulted from insecticidal protein co-expression in maize event MZIR098

Safety assessment of genetically modified plants includes protein characterization to confirm the intended trait protein expression. In addition, to conduct safety tests, the large amount of purified protein needed is usually met through the use of a surrogate, microbially produced protein source. Characterization of the eCry3.1Ab and mCry3A proteins as derived from Event MZIR098 maize was challenging because of the difficulty in purifying/isolating these proteins that are of similar molecular weight and have considerable shared sequence and immunogenicity. This also applies to establishing the biochemical equivalence to the microbially produced surrogate proteins, as highly-purified plant protein is required. While use of crude plant extracts facilitated functional equivalence testing with the surrogate proteins, a separate technical challenge had to be met. The eCry3.1Ab and mCry3A proteins display differentiated modes of action toward CRW pests, however, with the same overall target pest spectrum, no differential test organism existed to allow equivalence testing for one insecticidal protein in the presence of the other. To establish that the microbially produced proteins are suitable surrogates for the plant-produced proteins, the challenges in the protein purification and bioactivity testing had to be addressed. This article describes technical solutions to assess and characterize the insecticidal proteins in this new event and thereby confirm equivalence/suitability of the microbially produced protein surrogates.

Impact of Spodoptera frugiperda neonate pretreatment conditions on Vip3Aa19 insecticidal protein activity and laboratory bioassay variation

BACKGROUND

Variation in response to insecticidal proteins is common upon repetition of insect bioassays. Understanding this variation is a prerequisite to detecting biologically important differences. We tracked neonate Spodoptera frugiperda (J.E. Smith) susceptibility to Vip3Aa19 over 17 generations using standardized bioassay methods. Five larval pretreatment conditions and one bioassay condition were tested to determine whether susceptibility was affected. These included: storage time; prefeeding; storage at reduced temperature; storage at reduced humidity; colony introgression of field-collected individuals. Extremes of photoperiod during the bioassay itself were also examined.

RESULTS

LC50 values for two strains of S. frugiperda varied 6.6-fold or 8.8-fold over 17 generations. Storage time and humidity had no impact on Vip3Aa19 susceptibility, whereas prefeeding significantly reduced subsequent mortality (by 27%). Storage at reduced temperature increased mortality for one colony (from 45.6 to 73.0%) but not for the other. Introgression of field-collected individuals affected susceptibility at the first generation but not for subsequent generations. A 24 h bioassay photophase significantly reduced susceptibility (by 26%) for both colonies.

CONCLUSION

Certain pretreatment and bioassay conditions were identified that can affect S. frugiperda Vip3Aa19 susceptibility, but innate larval heterogeneity was also present. Our observations should help to increase the consistency of insecticidal protein bioassay results.