Spatial exposure-hazard and landscape models for assessing the impact of GM crops on non-target organisms

Pressure from insect-resistant maize on protected butterflies and moths

Intensification in agriculture affects many insect species, including butterflies. Insect-resistant crops, such as Bt (Bacillus thuringiensis) maize, which produces a toxin active against Lepidoptera, are an alternative to insecticide sprays. Genetically modified crops are regulated in most countries and require an environmental risk assessment. In the European Union, such assessments include the use of simulation models to predict the effects on nontarget Lepidoptera (NTL). To support the assessment of protected NTL, we extended an individual-based, stochastic, spatially explicit mathematical model (LepiX) to include a wider range of exposure scenarios, a species-sensitivity distribution, and an option for repeated exposure of individuals. We applied the model to transgenic maize DAS-1507, which expresses a high concentration of Bt toxin in pollen that may be consumed by NTL larvae on their host plants nearby. Even in the most conservative scenario without repeated exposure, mortality estimates for highly sensitive species ranged from 41% to 6% at distances of 10-1000 m from the nearest maize field. Repeated exposure can cause additional mortality and thus is relevant for the overall risk assessment. Uncertainties in both exposure and ecotoxicity estimates strongly influenced the predicted mortalities. Care should be taken to include these uncertainties in the model scenarios used for decision-making. In accordance with other modeling results, our simulations demonstrated that mean mortality may not be safe for protected species. With its high pollen expression, DAS-1507 maize may pose risks to sensitive and protected butterfly and moth species that may be difficult to manage. High expression of Bt toxin in pollen is unnecessary for controlling target pests. Consequently, we suggest that Bt maize with high pollen expression not be cultivated in regions where protected butterflies are to be conserved.

Phylogenetic analysis of the complete mitochondrial genome of the Japanese peacock butterfly Aglais io geisha (Stichel 1907) (Insecta: Lepidoptera: Nymphalidae)

The peacock butterfly Aglais io (Linnaeus, 1758) (Nymphalidae: Nymphalinae: Nymphalini) is a colorful and charismatic flagship butterfly species whose range spans from the British Isles and Europe through temperate Asia and the Far East. In Europe, it has been used as a model species for studying the effects of GMO maize pollen on caterpillar growth and survivorship. The Japanese subspecies, Aglais io geisha (Stichel 1907), is not as well studied as its European counterpart. Genome skimming by Illumina sequencing allowed the assembly of a complete circular mitochondrial genome (mitogenome) of 15,252 bp from A. io geisha consisting of 80.6% AT nucleotides, 13 protein-coding genes, 22 tRNAs, two rRNAs, and a control region in the gene order typical of butterfly species. Aglais io geisha COX1 gene features an atypical start codon (CGA) while COX1, COX2, CYTB, ND1, ND3, ND4, and ND5 display incomplete stop codons finished by the addition of 3' A residues to the mRNA. Bayesian phylogenetic reconstruction places A. io geisha within a clade with European A. io mitogenomes in the tribe Nymphalini, which is consistent with previous phylogenetic hypotheses.

EFSA is working to advance the environmental risk assessment of genetically modified crops to better protect butterflies and moths

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2021.EN-6443/full.

When the average hides the risk of Bt-corn pollen on non-target Lepidoptera: Application to Aglais io in Catalonia

Field cultivation of Genetically Modified (GM) Bt-plants has a potential environmental risk toward non-target Lepidoptera (NTLs) larvae through the consumption of Bt-maize pollen. The Bt-maize Cry protein targeting Lepidoptera species detrimental to the crop is also expressed in pollen which is dispersed by wind and can thus reach habitats of NTLs. To better assess the current ecological risk of Bt-maize at landscape scales, we developed a spatially-explicit exposure-hazard model considering (i) the dynamics of pollen dispersal obtained by convolving GM plants emission with a dispersal kernel and (ii) a toxicokinetic-toxicodynamic (TKTD) model accounting for the impact of toxin ingestion on individual lethal effects. We simulated the model using real landscape observations in Catalonia (Spain): GM-maize locations, flowering dates, rainfall time series and larvae emergence date of the European peacock butterfly Aglais io. While in average, the additional mortality appears to be negligible, we show significant additional mortality at sub-population level, with for instance a mortality higher than 40% within the 10m for the 10% most Bt-sensitive individuals. Also, using Pareto optimality we capture the best trade-off between isolation distance and additional mortality: up to 50 m are required to significantly buffer Bt-pollen impact on NTLs survival at the individual level. Our study clears up the narrow line between diverging conclusions: those claiming no risk by only looking at the average regional effect of Bt on NTLs survival and those pointing out a significant threaten when considering the variability of individuals mortality.

The impact of Bt maize expressing the Cry1Ac protein on non-target arthropods

From 2014 to 2016, individuals of the principal non-target arthropod (NTA) species in a field of Bt maize expressing the Cry1Ac protein (Bt38) were compared to those in a control field of the corresponding non-transformed near isoline (Z58). For all 3 years, the population dynamics and biodiversity of NTAs were analyzed to determine if any differences might be attributable to the genetically modified (GM) maize being evaluated. The main NTAs in these fields were Aphidoidea, Pentatomidae,Araneae, and Coccinellidae. Temporal variation in NTA diversity across sample dates within a year showed no significant differences between the Bt maize and the non-Bt maize field in the total number of individuals of the dominant arthropod species per 25 plants, the Shannon index (H), Pielou index (J), Simpson index (D), and Bray-Curtis index. The cultivation of Bt corn failed to show any detrimental evidence on individuals, H, J, D, and Bray-Curtis index of NTAs, and these parameters were identical in Bt and non-Bt corn plots. These results provide further evidence of the lack of ecological impact of GM maize.

A Spatio-Temporal Exposure-Hazard Model for Assessing Biological Risk and Impact

We developed a simulation model for quantifying the spatio-temporal distribution of contaminants (e.g., xenobiotics) and assessing the risk of exposed populations at the landscape level. The model is a spatio-temporal exposure-hazard model based on (i) tools of stochastic geometry (marked polygon and point processes) for structuring the landscape and describing the exposed individuals, (ii) a dispersal kernel describing the dissemination of contaminants from polygon sources, and (iii) an (eco)toxicological equation describing the toxicokinetics and dynamics of contaminants in affected individuals. The model was implemented in the briskaR package (biological risk assessment with R) of the R software. This article presents the model background, the use of the package in an illustrative example, namely, the effect of genetically modified maize pollen on nontarget Lepidoptera, and typical comparisons of landscape configurations that can be carried out with our model (different configurations lead to different mortality rates in the treated example). In real case studies, parameters and parametric functions encountered in the model will have to be precisely specified to obtain realistic measures of risk and impact and accurate comparisons of landscape configurations. Our modeling framework could be applied to study other risks related to agriculture, for instance, pathogen spread in crops or livestock, and could be adapted to cope with other hazards such as toxic emissions from industrial areas having health effects on surrounding populations. Moreover, the R package has the potential to help risk managers in running quantitative risk assessments and testing management strategies.

Evaluation of the potential exposure of butterflies to genetically modified maize pollen in protected areas in Italy

Environmental impacts of genetically modified crops are mandatorily assessed during their premarket phase. One of the areas of concern is the possible impact on nontarget organisms. Crops expressing Cry toxins might affect Lepidoptera larvae living outside cultivated fields, through pollen deposition on wild plants, which constitute their food source. While pollen toxicity varies among different events, possible exposure of nontarget species depends on the agro-environmental conditions. This study was conducted in two protected areas in Italy, characterized by different climatic conditions, where many Lepidoptera species thrive in proximity to maize cultivations. To estimate the possible exposure in absence of the actual stressor (e.g., Cry1-expressing maize plants), we conducted a two-year field survey of butterflies and weeds. Indicator species were selected-Aglais (Inachis) io in the Northern site and Vanessa cardui in the Southern site-and their phenology was investigated. Pollen dispersal from maize fields was measured by collection in Petri dishes. Duration and frequency of exposure was defined by the overlap between pollen emission and presence of larvae on host plants. Different risk scenarios are expected in the two regions: highest exposure is foreseen for A. io in the Northern site, while minimal exposure is estimated for V. cardui in the Southern site. In the latter case, locally grown maize cultivars flower in mid-summer in coincidence with an aestivation period for several butterfly species due to hot and dry conditions. Moreover, host plants of V. cardui are at the end of their life cycle thus limiting food availability.