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New publication on impact of Bt protein on ladybird larvae

GM maize and the two-spot ladybird: The scientific debate continues

Bt protein can have a harmful effect on ladybird larvae, according to a new publication by the Swiss Federal Institute of Technology (ETH) in Zurich. The report claims to confirm similar results from 2009, which were used to justify the German ban on cultivating Bt maize MON810. The scientific debate about the laboratory methods used, the laboratory results and their significance for the situation in the field is not yet over.

Angelika Hilbeck, Institute of Integrative Biology, ETH Zurich

Jörg Romeis, Agroscope research institute, Zurich The scientists disagree on whether two-spot ladybirds could be at risk because of Bt maize.

In 2009, Angelika Hilbeck’s team at ETH Zurich published laboratory findings that showed that larvae of the two-spot ladybird can be harmed by Bt protein. This publication played a key role in justifying the cultivation ban for Bt maize MON810 in Germany, which was imposed by Germany’s Environment Minister Ilse Aigner in April 2009.

The research findings of Hilbeck’s group contradict a number of other results from the laboratory and field, which found that Bt maize is not likely to have negative effects on ladybirds. These results were also cited by Germany’s Central Commission for Biological Safety in a statement it issued in 2011. In 2010 a paper was published by Jörg Romeis and his team at Switzerland’s public Agroscope research station in Zurich, which assessed the findings of Hilbeck’s group and presented new research. According to this, the quantities of Bt protein that ladybird larvae are exposed to in the field are not expected to have any negative impacts on the larvae.

In February 2012, the Hilbeck group published a further study, primarily in response to the 2010 publication of the Romeis group. They accuse the Romeis group of using a different test method. Hilbeck et al. write that they have demonstrated that this other test method is the reason for the difference in the results. Combining the test methods from both groups showed, they say, that Bt protein can indeed have a harmful effect on two-spot ladybird larvae.

Do ladybird larvae suck or bite their food?

For the Hilbeck group’s study in 2009, ladybird larvae were fed on flour moth eggs that had been sprayed with Bt protein solutions in various concentrations. The scientists found a higher mortality rate among the larvae fed in this way than in the control groups and concluded that the two-spot ladybird might be harmed by Bt maize.

Other scientists criticised the fact that the larvae could not have eaten any appreciable quantity of Bt protein anyway, because young ladybird larvae only suck their food dry. For their study published in 2010, Jörg Romeis’s group observed individual ladybird larvae under the microscope and established that they did in fact only suck the insides out of the flour moth eggs. In no cases were larvae found to have eaten even a part of the egg casing. The group therefore found it necessary to modify the test method.

In 2012, Hilbeck et al. also observed ladybird larvae under the microscope as they fed on flour moth eggs. They write that the larvae bite into the eggs and that when the contents spill out, they come into contact with the egg casing. According to the study authors, it was therefore possible for the larvae to have eaten Bt protein that had been sprayed on the egg casing.

It’s the dose that counts

The study published by the Romeis group in 2010 presents the results of two series of trials, only one of which is mentioned by Hilbeck et al. (2012). In this trial, ladybird larvae were fed a sugar solution containing purified Bt protein. The larvae were also given untreated flour moth eggs as a source of protein. No significant differences in larval development were observed between this group and the control group that received the nutrient solution without Bt protein.

Hilbeck et al. accuse the Romeis group of exposing the larvae to insufficient doses of the Bt protein, which is why no effect was observed. The feeding experiment conducted by the Hilbeck group in 2009 using sprayed flour moth eggs ran continuously for ten days. In the experiment conducted by the Romeis group however, the sugar solution containing Bt protein was only offered to the larvae four times – for 24 hours at the start of each new larval stage. In order to show that this dose is inadequate, Hilbeck et al. conducted an experiment with European corn borer larvae in 2012. One group was fed Bt maize continuously for seven days, while the other group received Bt maize once for 24 hours. All the larvae in the first group died. In the second group, only some of the larvae died.

Hilbeck et al. (2012) developed a new experiment method combining the approaches used by both groups in their previous publications. Ladybird larvae were given a sugar solution containing Bt protein, as well as flour moth eggs sprayed with Bt protein, continuously for six days. The mortality rate of the larvae fed on this diet was much higher than in the control group.

The significance of laboratory results

Hilbeck et al. (2012) write explicitly that the research methods they describe are suitable only for detecting a potential risk. Further studies would have to be carried out to clarify the matter. Back in 2009 they wrote that ladybird larvae in the field would only be exposed to potentially harmful quantities of Bt protein if they fed on Bt maize pollen or on prey such as red spider mites, which accumulate Bt protein. However, they would not come into contact with Bt protein through their usual primary food source, aphids, because aphids only suck up plant sap, which does not contain Bt protein. Hilbeck et al. (2012) do not address the feeding trials that the Romeis group conducted with prey organisms.

The scientific debate about whether Bt proteins can in theory harm ladybird larvae and which laboratory methods are the best for researching the question is likely to continue for a while longer. However, field trials have not yet found that the cultivation of Bt maize has reduced the population density of ladybirds. The cultivation ban on MON810 is still based on the findings of Angelika Hilbeck’s team.

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