Bt maize not harmful to ladybirds
Genetically modified maize has no harmful impacts on the two-spotted ladybird. This is the finding of a scientific study published in August 2010. It contradicts a similar study published in 2008, which the German minister of agriculture, Ilse Aigner, cited when justifying the German ban on cultivating MON810 Bt maize.
Ladybirds are among the insects that live in maize fields. The 2009 ban on cultivating MON810 Bt maize was based in part on a study that had found harmful effects on ladybirds. Now a new study has been published with different findings.
The conclusions in the 2008 study contradict numerous other studies that have found no negative impacts of Bt maize or Bt proteins on ladybirds. As part of the study, 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-spotted ladybird might be harmed by Bt maize. The publication was used, along with others, to justify the ban on MON810 cultivation announced by Germany’s minister of agriculture, Ilse Aigner, in April 2009.
Other scientists expressed serious doubts about the study findings, saying among other things, that no clear dose-effect relationship had been found. The mortality rate did not increase in line with the Bt protein concentration sprayed on the flour moth eggs. In addition, the mortality rate in some control groups, in which the food had not been sprayed with Bt protein, was unusually high. Moreover, the study was criticised for the fact that it was not clear how much Bt protein had been applied to the eggs and how many moth eggs the larvae had eaten. In the view of the study’s critics, the larvae could not have eaten any appreciable quantity of Bt protein anyway, because young ladybirds only suck their food dry.
The new study reassessed the possible impact that Bt proteins might have on two-spotted ladybirds. It aimed to clarify, first of all, whether the larvae eat flour moth eggs in their entirety or whether they just suck them dry. Young ladybird larvae were given individual flour moth eggs and were observed while they consumed the eggs. It was found that they only suck the eggs dry. In no cases were larvae found to have eaten even a part of the outside.
To ensure that the ladybird larvae ingested a biologically relevant quantity of Bt protein, the new study used red spider mites as a food source. Red spider mites feed on maize, among other things, and of the ladybird’s natural prey organisms they are the ones that accumulate the most Bt protein. The exact amount was measured using an ELISA test. Ladybird larvae were fed exclusively on red spider mites that had previously been fed on Bt maize. The mortality of these larvae was not significantly different from that of the control group, which was given red spider mites that had been fed on conventional maize.
Finally, the ladybird larvae were fed with purified Bt protein in a nutrient solution, at a concentration ten times higher than that found in the red spider mites. No significant differences in larval development were observed between this group and the control group that received the nutrient solution without Bt protein. In another control group, substances were added to the nutrient solution that are known to be toxic to ladybirds. In this group, the mortality rate was significantly higher and the surviving larvae developed more slowly. This shows that the trial design is suitable in principle for demonstrating harmful effects of components of the feed solution.
Since the ladybird larvae in the experiment were exposed to much higher Bt protein quantities than they would be expected to consume in the field, the authors conclude that the cultivation of Bt maize has no harmful effects on the two-spotted ladybird.