Background:  In 2008/2009, Schmidt and colleagues published a study reporting lethal effects of the microbial Bt toxins Cry1Ab and Cry3Bb on the coccinellid biological control organisms Adalia bipunctata. Based on this study, in concert with over 30 other publications, Mon810 cultivation was banned in Germany in 2009. This triggered two commentaries and one experimental study all published in the journal 'Transgenic Research' that question the scientific basis of the German ban or claim to disprove the adverse effects of the Bt toxins on A. bipunctata reported by Schmidt and colleagues, respectively. This study was undertaken to investigate the underlying reasons for the different outcomes and rebuts the criticism voiced by the two other commentaries.
Results:  It could be demonstrated that the failure to detect an adverse effect by Alvarez-Alfageme and colleagues is based on the use of a significantly different testing protocol. While Schmidt and colleagues exposed and fed larvae of A. bipunctata continuously, Alvarez-Alfageme and colleagues applied an exposure/recovery protocol. When this exposure/recovery protocol was applied to a highly sensitive target insect, Ostrinia nubilalis, the lethal effect was either significantly reduced or disappeared altogether. When repeating the feeding experiments with the Bt toxin Cry1Ab using a combined protocol of both previous studies, again, a lethal effect on A. bipunctata larvae was observed. ELISA tests with Bt-toxin fed larvae and pupae confirmed ingestion of the toxin.
Conclusions:  The new data corroborates earlier findings that Cry1Ab toxin increases mortality in A. bipunctata larvae. It was also shown that the different applied testing protocols explained the contrasting results.