Adverse effects of Bt toxins on water insects

[img_assist|nid=104|title=|desc=|link=none|align=left|width=100|height=43]Rosi-Marshal et al. (2007) just published a long overdue study about whether Bt plant residues got into headwaters during or after cultivation, and whether the Bt-toxin would have adverse effects on water insects like caddies flies, close relatives to butterflies. In both cases the answer was yes. This laboratory study gives enough indication to at least include water insects in the monitoring of Bt crops.

But the study also points out another relevant problem: The isolines of Bt-maize were unsuitable as a control in this a study where decomposition played a role.

Isolines are supposed to be identically with the transgenic lines with the exception of the inserted gene construct(s) and the related trait. But Bt maize was found not only to produce the desired Bt toxin, but also to have higher lignin contents Saxena & Sotzky 2001) - so there are two differences instead of one. But if the isolines aren't as they should: How do you know if an effect might be caused by the Bt toxin or maybe by differences in decomposition or in the food qualitiy of Bt residues with lower or higher lignin concentrations.

Rosi-Marshall et al. (2007) in this study solved this problem by not using isogenic lines, but by choosing conventional varieties that matched the transgenic lines in lignin content and C/N ratio. For future studies it might be necessary to use two controlls: the isogenic line as well as lines with matching lignin levels. And maybe it is high time that somebody found out why lignin concentration in Bt maize are different to start with.