Limitations in dose–response and surrogate species methodologies for risk assessment of Cry toxins on arthropod natural enemies

Abstract

Dose-response assays and surrogate species are standard methods for risk analysis for environmental chemicals. These assume that individuals within a species have unimodal responses and that a surrogate species can predict responses of other related taxa. We exposed immature individuals of closely related aphidophagous coccinellid predators, Cycloneda sanguinea and Harmonia axyridis, to Cry1Ac and Cry1F toxins through uniform and constant artificial tritrophic exposure through Myzus persicae aphids. Both toxins were detected in coccinellid pupae, with individual and interspecific variation. Uptake was significantly higher in H. axyridis than in C. sanguinea, both in the proportion of individuals and the concentrations per individual. We also observed bimodal uptake of the Cry toxins by H. axyridis, which indicated that some individuals had low bioaccumulation and some had high bioaccumulation. This suggests that standard dose-response assays need to be interpreted with caution and future assays should examine the modality of the responses. In addition, the similarity in the biological effects of the Cry toxins in the two predators was due to different biological exposure mechanisms. The majority of H. axyridis were exposed both internally and in the gut, while C. sanguinea was exposed primarily in the gut. Thus, despite their close phylogenetic relatedness, these species would not be good surrogates for each other and the surrogate species methodology should be tested more rigorously.

Efficiency of biological control for fall armyworm resistant to the protein Cry1F

“…This highlights the need to perform biosecurity studies for the approvement of GM cultivars (guidlines nº 6 of 2008 and nº 8 of 2009, CTNBio, 2009). The majority of studies found in the literature (Romeis et al, 2006(Romeis et al, , 2008Mendes et al, 2012a;Leite et al, 2014;Tian et al, 2015;Paula et al, 2016) generally present results different to those in this study, since they evaluate the direct and indirect effects of Bt cultures on non-target organisms using susceptible prey and that feed on the Bt plant moments before exposure to the predators. In the present study, the prey were obtained from genitors resistant to the protein Cry1F.…”

Impact of transgenic soybean expressing Cry1Ac and Cry1F proteins on the non-target arthropod community associated with soybean in Brazil

“…The extrapolation of results from lower-tiered studies to inform risk assessments that consider the potential for field effects is well supported in the Bt literature, where meta-analyses examining correlation of laboratory and field data concluded that laboratory results generally predict [ 17 ] or over-estimate field effects [ 18 ]. Building on the lessons from empirical testing and the evolution of risk assessment for GM crops [ 7 – 16 ], the risk assessment community recognized that surrogate organism testing [ 14 ] and data transportability [ 19 ], when appropriately applied [ 20 ], provide high value through informing and simplifying risk assessments performed across geographies in which the same crop is cultivated [ 21 ]. While lower tier hazard assessments have generally predicted low risk for Bt crops to NTA’s under field conditions, field studies are sometimes required by government regulatory bodies allowing this prediction to be tested empirically [ 16 ].…”

Evaluation of Cry1Ac and Cry2Aa Toxin Binding to Two Important Beneficial Cotton Field Insects, Harmonia axyridis and Orius similis

“…For example, the Cry1Ac toxin was reported to be absorbed and bioaccumulate not only in the gut of H. axyridia but also in the body. 23,24 Consequently, we were interested in testing accumulation of Cry1Ac and Cry2Aa in total protein extracts of H. axyridia and O. similis. Since larvae/nymphs and adult stages can be exposed to toxins directly or indirectly, 3,11 we used total protein extracts from larvae/nymphs and adults in order to get more accurate and complete results.…”

“…axyridis, and the predatory flower bug, Orius similis, are two important predators in cotton fields. ,,, Accumulation of Cry toxins through the food chain or after direct feeding on Bt pollen/anther was shown in these two predators. ,,, Moreover, several articles reported that Cry toxins were also absorbed and bioaccumulated in the body of H. axyridis, ,, indicating a potential increase of environmental risks of Cry toxins to these species. In the current study, we investigated the binding potentiality of Cry1Ac and Cry2Aa to these two important predators.…”