Effects of Bt maize on various arthropods
Maize in heat stress
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August 2003. The marks left on this trial field by this summer’s heat and drought are clear for all to see. The maize plants are on average at least 20 centimetres smaller than last August. In some places they are now barely a metre high. Where there are cobs, they are much smaller than usual. In some cases there is only one puny cob with just a few kernels. When the male flowers released their pollen, the female flowers were not yet far enough developed to be able to catch the pollen grains with their silks. Farmers intend to harvest the maize on the surrounding fields at the end of August – four weeks earlier than usual. While they are complaining of drastic yield losses, not much has changed for the biologists at RWTH Aachen University. This is the third year that they are investigating the effects that Bt maize might have on various arthropods . As in previous years, they empty pit traps, collect pollen and count animals. "That was quite hard work in this heat", admits project leader Achim Gathmann. Some species benefit from the heat, others are afflicted by it. "But we are still collecting enough animals." The European corn borer has also bored its way into some plants, as it did last year. Bent stems are an unmistakable sign of corn borer activitiy. |
Extreme trial conditions.
This summer’s drought period does represent extreme conditions for the experiment – but they are the same for all trial plots: those with Bt maize and those with isogenic control plants with and without insecticide treatment. What the biologists are interested in are differences in the organism counts and species spectrum between the different types of plot. It is, however, conceivable in theory that heat and drought stress might aggravate potential Bt toxin effects on the arthropods under investigation. The extreme weather conditions might act like a burning glass, under which otherwise barely noticeable Bt effects become more apparent.
Apparently, the position of a maize plant has a big influence on how it reacts to heat and drought. On the two trial fields, separated by barely 500 metres, the maize plants exhibit considerable height differences. Inside a field the differences are still more striking: a few metres from a group of robust maize plants with well-formed cobs and green leaves there are small, brown, withered plants. Even small-scale differences in soil condition, e.g. in storage ability for soil moisture, have serious impacts on how the plants cope with heat and drought stress.
If there are any Bt effects on the arthropods under investigation, they are being overshadowed by the site effects, which are particularly apparent this summer. Whether it is possible to differentiate between the two remains to be seen.
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