Is the German suspension of MON810 maize cultivation scientifically justified?

The GSO refers solely to Schmidt et al. (2009), which is discussed above.

The GSO refers to Losey et al. (1999) and Jesse and Obrycki (2000) who concluded a potential threat to the Monarch butterfly in laboratory force-feeding experiments (see Introduction). The GSO cites a publication by Hellmich et al. (2001) which describes laboratory tests to establish the relative toxicity of various Cry toxins: their data suggest that pollen from the Cry1Ab varieties Bt11 and MON810 would have no acute effects on the Monarch butterfly in a field setting and that only the Bt176 varieties can affect these butterflies, a conclusion confirmed by Zangerl et al. (2001), also cited in the GSO, who found sublethal effects of Bt176 on black swallowtails (Papilio polyxenes) in the field. Surprisingly, the GSO does not mention Wraight et al. (2000) who, in contrast, failed to detect a harmful effect of MON810 pollen on black swallowtails. Dively et al. (2004) studied continuous exposure to pollen (during maize anthesis) of Monarch larvae in force-feeding trials. They found that 24% fewer larvae exposed to Bt pollen reached the adult stage. However, taking into account the high natural mortality of larvae and the proportion of larvae actually exposed to pollen, they calculated that the risk associated with long term exposure is only 0.6% additional mortality, a conclusion, again, not mentioned in the GSO.

The GSO also cites a number of publications by Felke and coworkers (see the German federal website www.gmo-safety.eu/en/safety_science/136.docu.html). A summary report by Felke and Langenbruch (2005) states: “We recommend only permitting cultivation of Bt-Maize with negligible toxin expression in pollen”, which is the case of MON810. The authors did not demonstrate harmful effects on butterflies with MON810 in contrast to Bt176.

The most recent references cited in the GSO are laboratory studies, namely Mattila et al. (2005) who used a MON810 hybrid producing two toxins (Cry1Ab and Cry2Ab2) and MON863 producing Cry3Bb1 (with force-feeding results similar to those of Dively et al. 2004), and Lang and Vojtech (2006) who used again Bt176 maize.

In conclusion, the GSO does not provide any evidence for deleterious effects of MON810 on Lepidoptera under field conditions. In addition, the GSO uses arguments concerning Bt176 to argue for a suspension of MON810 varieties, which is incorrect since scientific risk assessment follows a case-by-case procedure.

The GSO mentions the publication by Rosi-Marshall et al. (2007) suggesting that toxins in transgenic crop byproducts may affect headwater stream ecosystems. Maize byproducts were measured in headwater streams adjacent to maize fields. This work also showed the presence of maize pollen grain in trichopteran insects collected in such streams. However, this work did not report deleterious effects on these insects under natural conditions. Only laboratory conditions (force-feeding experiments) with two trichopteran species (caddisflies) were reported. They showed no effect on mortality for either Lepidostoma liba fed maize litter or for Helicospyche borealis fed maize pollen at the highest concentration measured in water streams. In the latter case, a higher mortality of H. borealis was observed only at higher pollen concentrations, and in the former, L. liba had a 50% reduced growth rate.

In two letters, five scientists criticized this article on several grounds, including the fact that the control maize was not isogenic to the Bt maize, raising the possibility that the observed differences were due to differences in the chemical composition of the leaves, with no link to the Cry1Ab toxin (Beachy et al. 2008; Parrott 2008). Rosi-Marshall et al. (2008) replied to these criticisms agreeing on the point that their article should not have suggested their observations have “ecosystem-scale consequences”. Indeed, the same laboratory failed to observe any effect on growth or mortality for two trichopteran species during in situ experiments (Pokelsek et al. 2007).

Griffiths et al. (2009) studied headwater streams draining agricultural landscapes and receiving maize leaves via wind and surface runoff and examined how substrate quality and in-stream nutrient concentrations influenced microbial respiration on maize. They found that Bt maize had a faster decomposition rate than non-Bt maize, while microbial respiration rates did not differ between Bt and non-Bt maize. Decomposition rates were not negatively affected by genetic engineering, most likely because the Bt toxin does not adversely affect the aquatic microbial assemblage involved in maize decomposition. Additionally, shredding caddisflies, which were studied by Rosi-Marshall et al. (2007), were depauperate in these agricultural streams, and most likely did not play a major role in maize decomposition.

The GSO also mentions a publication by Bohn et al. (2008), which was examined above, and by Douville et al. (2007). The latter study measured the persistence of DNA (not insecticidal proteins) in surface water. The half-life of the cry1Ab DNA was identical when produced by Bt maize or by B. thuringiensis (widely used as a biopesticide). Traces of transgenic DNA (0–0.0000005 ng/l) were found in a river up to 82 km from a field (however, the authors did not demonstrate that it originated from this actual field). The same surface water samples contained 0–30 ng/l total DNA. It is unclear why the mere presence of DNA, a normal component of terrestrial and aquatic ecosystems, should be viewed as a threat to these ecosystems.

Douville et al. (2005) published another similar study which measured levels of the insecticidal protein in surface water. They found that the Cry1Ab protein produced by Bt maize disappeared more rapidly than its counterpart produced by B. thuringiensis (which was expected from its crystal structure). The authors concluded that this protein is “fairly uncommon” in aquatic environments.

The GSO refers to a poster by Büchs et al. (2004) on the effects observed in laboratory trials involving sciarid fly larvae fed on pollen or plant parts from different maize varieties. Two Bt varieties and their respective isogenic parent varieties were involved in the study, alongside a third conventional variety. The authors stressed only one of the results: sciarid fly larvae fed on straw from MON810 Bt maize took longer to pupate (ca. 21 days instead of ca. 18 on average). However, no correlation was found between the observed effect and the absolute toxin content of different maize varieties. This effect may, therefore, be linked to the nutritional quality of the feed. Similar effects were also observed between different conventional varieties in the same experiments. In an interview (www.gmo-safety.eu/en/maize/soil/308.docu.html), the authors reported inconsistent trends in field experiments over 3 years and suggested “closer observation in post-market monitoring”.

In summary, the references cited in the GSO do not validate its claim on ecotoxicological effects of MON810 maize on non-target arthropods. Since the GSO appears to be based on an incomplete list of references, we provide a more complete literature survey below.

Regarding the distribution of recent publications on the impact on non-target arthropods, we observe that the vast majority of the articles dealing with MON810 or Cry1 (n = 23) indicates that this ‘event’ has no impact on these organisms. Only two articles (noted “a” in the table) indicate a deleterious effect on non-target arthropods (Górecka et al. 2008; Zenner de Polania and Alvarez Alcaraz 2008). The other articles do not deal with Cry1.

Górecka et al. (2008) measured the braconid Aphidius colemani population when feeding on bird cherry-oat aphid (Rhopalosiphum padi), which were feeding on Bt or non-Bt maize under greenhouse conditions. In an experiment during the summer, they found a higher A. colemani population on Bt-fed aphids, while they found the opposite during the winter experiment. The authors conclude that “the observed effect of season on parasitation level by A. colemani on R. padi host feeding on Bt and non-Bt maize plants indicates that results obtained in a single greenhouse experiment may lead to questionable conclusions and should be confirmed by other experiments”.

Zenner de Polania and Alvarez Alcaraz (2008) carried out field observations and laboratory studies for 3 years to evaluate the effect, direct or indirect, of Bt maize (‘Yieldgard’ hybrid) on the natural enemies of the main insect pest, Spodoptera frugiperda. Their results indicated that the Cry1Ab toxin exhibits an indirect effect on these beneficial insect populations. They observed a tendency for a decrease in S. frugiperda populations in commercial fields of both transgenic and conventional varieties. The responsible factors are insecticidal applications and the control of the prey/host (S. frugiperda) by Bt maize varieties.

Our review leads to 75 articles. Among them, 27 concern Bt maize and ladybirds, of which 21 indicated that there is no effect of Bt maize on ladybirds. The remaining six articles mention some effects of Bt proteins on non-target organisms such as ladybirds and are discussed below. Among them, the publication of Schmidt et al. (2009) has already been discussed above.

Wold et al. (2001) found no significant within-year differences in the overall density of beneficial insect populations including predatory coccinellids (Adalia bipunctata and Coleomegilla maculata), chrysopids and anthocorids between Bt and non-Bt sweet corn. Note that A. bipunctata was also used in the study of Schmidt et al. (2009). Although the test of mean density of insects per three plants in open plots detected a significant trend for a higher density of C. maculata in non-Bt maize (1.92) compared to Bt maize (1.17), the results were inconsistent from 1 year to another and it is unclear whether it is actually linked to the Bt trait.

Delrio et al. (2004) showed in field studies that the infestation of aphids, mainly Rhopalosiphum padi, was similar in both Bt and non-Bt plots. Similarly, no significant difference was found between Bt and non-Bt maize for predator counts (arachnids, mirids, anthocorids, syrphids, chrysopids and coccinellids) on sample plants. However, when predator abundance was estimated by their capture on yellow traps, a single difference was reported, namely in the total number of coccinellids, mainly Propylea quatuordecimpunctata, which was significantly lower in Bt plots.

Toth et al. (2004) compared the applicability of two arthropod sampling methods, namely “spider-web survey” and “whole plant visual sampling”, in a risk assessment study. Both methods were able to detect significant differences in the quantity of predatory insects in Bt (MON810) versus isogenic plots, but not in the same taxa. More Nabidae were found in Bt versus isogenic plots using the spider-web method, while more Coccinellidae were found in isogenic plots versus Bt using the plant sampling method. The authors conclude that “due to several biological uncertainties, interpretation and explanation of the results remain problematic”.

Hoheisel and Fleischer (2007) showed the influence of concurrent introduction of three transgenic vegetable varieties on the seasonal dynamics of coccinellids and their food, aphids and pollen, examined within diversified farm systems practicing insect pest management. The transgenic varieties used included sweet corn, potato and winter squash expressing Cry1Ab, Cry3A and plant viral coat proteins targeting Lepidoptera, Coleoptera and aphid-transmitted viruses, respectively. Transgenic systems reduced insecticides by 25%. Weekly differences in coccinellid density between transgenic and isogenic crops were rare and transitory, governed by the timing of planting or foliar insecticide use patterns.

Recently, under controlled conditions, Moser et al. (2008) confirmed that two species of coccinellids can feed directly on maize. Development time of one species increased after Bt maize treatments compared with non-Bt corn treatments.

Our systematic review leads to 376 articles. Among these, 8 mentioned effects.

Orr and Landis (1997) recorded predation and parasitism of the European corn borer in Cry1Ab and isogenic maize fields. Levels of egg mass predation and parasitism, density of European corn borer predators and parasitism of larvae were not significantly different between the transgenic and isogenic plots. All observed differences in natural enemy population parameters were opposite to expected if transgenic plants had an adverse impact.

Bourguet et al. (2002) performed a field experiment at two sites comparing the temporal abundance of non-target arthropods in Bt maize (MON810 hybrid) and non-Bt maize. The non-target insects studied included the aphids Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae, the bug Orius insidiosus, the syrphid Syrphus corollae, the ladybird Coccinella septempunctata, the lacewing Chrysoperla carnea (Stephens), thrips and hymenopteran parasitoids. For all but one species, the number of individuals varied greatly over the season but did not differ between the maize types. The only exception was thrips which, at one site, were significantly more abundant in Bt maize than in non-Bt maize. However, this difference did not remain significant when the multiple tests were taken into account.

Candolfi et al. (2004) found no effect of Bt maize on the communities of soil-dwelling and non-target plant-dwelling arthropods. A trend towards a community effect on flying arthropods was observed with a lesser abundance of adult Lepidoptera, flies in the families Lonchopteridae, Mycetophilidae and Syrphidae, and the hymenopteran parasitoids Ceraphronidae. However, the effects were slight and restricted to two sampling dates corresponding to anthesis. In contrast, a short but statistically significant effect of two insecticides was observed on the community of plant dwellers and a prolonged effect of one insecticide on the soil dwellers.

Pilcher et al. (2005), when measuring adult populations of five predator and one parasitoid species in maize plots in three locations in Iowa over several years, found few differences in abundance of the generalist predators between Bt and non-Bt maize. However, the specialist parasitoid of the European corn borer was significantly affected in Bt plots, which was not unexpected given its dependence on the presence of the European corn borer.

Bruck et al. (2006) found less Macrocentrotus cingulum and Nitidulidae in transgenic plots (MON810) probably due to the absence of the European corn borer which serves as a host for M. cingulum and provides a habitat for Nitidulidae, which are known to frequent European corn borer tunnels. Application of a conventional insecticide for European corn borer control had a broader impact on populations of various non-target arthropods.

Griffiths et al. (2007) found no effect of Bt maize (MON810) on microarthropods, enchytreids and earthworms, but they found a difference concerning the microbial community structure. However, this difference was not persistent and could not be distinguished from a varietal effect. They concluded that there were no soil ecological consequences for these communities associated with the use of Bt maize in place of conventional varieties. Other land management options, such as tillage, crop type and pest management regime, had significantly greater effects on the biology of the soil rather than the type of maize grown.

Toschki et al. (2007) recorded the activity abundance of spiders and carabid beetles in Bt maize (MON810), an isogenic variety and the isogenic variety treated with insecticide. Significantly different activity abundances in Bt plots compared with isogenic control plots were observed both for spiders and carabid beetles during 2001. However, in 2002 and 2003 they found no changes in community structure with any of the treatments. They hypothesized that the change in the first year may have been caused by the influence of a massive corn borer infestation and accompanying large changes in microclimatic factors.

Musser and Shelton (2003) found a positive effect on the Bt transgenic pest control in sweet corn. In field trials they found that transgenic Bt sweet corn and also the foliar insecticides indoxacarb and spinosad are all less toxic to the most abundant predators in sweet corn (Coleomegilla maculate, Harmonia axyridis, and Orius insidiosus) than the pyrethroid lambda cyhalothrin. Indoxacarb, however, was moderately toxic to coccinellids and spinosad, and indoxacarb was somewhat toxic to O. insidiosus nymphs at field rates. Their results “demonstrate that some of the new products available in sweet corn allow a truly integrated biological and chemical pest control program in sweet corn, making future advances in conservation, augmentation and classical biological control more feasible”.

One should keep in mind that, compared to these 7 publications mentioning some minor negative effects, there are 37 other papers indicating no effect of Bt maize on non-target organisms. Nevertheless, in order to clarify whether the effects mentioned occasionally in research studies represent a real trend or not, we have examined the conclusions of recently published meta-analyses.

We will focus here on field experiments. However, it should be mentioned that Lövei et al. (2009) reviewed 55 laboratory studies on the impact of GM plants on arthropod natural enemies. They conclude that these proteins “often have non-neutral effects on natural enemies” and “although there are data on 48 natural enemy species, the database is still far from adequate to predict the effect of a Bt toxin or proteinase inhibitor on natural enemies”. Shelton et al. (2009) published a rebuttal of these interpretations stating that Lövei et al. (2009) conducted a data-mining exercise without prior elaboration of a risk hypothesis framework (Romeis et al. 2008), used inappropriate and unsound methods for risk assessment that have led them to reach conclusions that are in conflict with those of several recent comprehensive reviews and meta-analyses. The latter are summarized below.

In a systematic review, Romeis et al. (2006b) found that field studies generally confirmed that the abundance and activity of parasitoids and predators are similar in Bt and non-Bt crops. As far as MON810 is concerned, they compiled two field studies (Bourguet et al. 2002; Manachini 2003) which observed a lesser abundance of specialist enemies of the pest targeted by Bt maize. This is a consequence of the efficient control of target pest insects such as the European corn borer by Cry1Ab maize. Indeed, without their favorite prey or host, these specialists will not be attracted to the maize field.

Marvier et al. (2007) published a meta-analysis of 42 field experiments examining the effects of insect-protected cotton and maize. They noted that certain non-target taxa were less abundant in Bt fields compared to insecticide-free fields. For Cry1Ab plants, they emphasized the less abundant parasitic wasps of the braconidae and ichneumonidae.

In another meta-analysis, Wolfenbarger et al. (2008) also observed that insecticide effects were much larger than those of Bt crops. In maize, these analyses also revealed a reduction of parasitoids in Bt fields. Examination of the 116 observations showed that most of these reductions (n = 93) concern Macrocentrus grandii, a specialist parasitoid of the Bt target, the European corn borer. Higher numbers of the generalist predator, Coleomegilla maculata, were associated with Bt maize but numbers of other common predatory genera were similar in Bt and non-Bt maize. No significant effects of Bt crops on detritivores were found.

Naranjo (2009) agrees with the above analysis in concluding that “the minor negative effects of Bt crops demonstrated in the field pale in comparison with alternative pest suppression measures based on insecticides”. These systematic reviews and meta-analyses agree on the fact that the lower abundance of some insects mainly concerns specialized enemies of the target pest (an expected consequence of its control).