Low yields

SiFo project researchers who are studying the effects of Diabrotica-resistant Bt maize on the maize ecosystem have come from Aachen to empty the pit traps and catch insects living in the ground vegetation or visiting the flowers before the next rainfall.

A researcher walks through the rows of maize with a large net to catch arthropods in the ground vegetation, like cicadas, and their antagonists, such as reduviid bugs.

Very few insects have been found this year. After this ‘run’ there are just a few cicadas and two reduviid bugs in the net. The insects will be transferred to small glass jars and then counted and identified in the laboratory. The Bt toxin concentrations in the netted insects will also be studied, to find out the extent to which different species come into contact with it, either directly through plant consumption, or indirectly through prey.

The trial field, which measures around 6 hectares, has been divided into 32 plots planted with maize: eight plots with Bt maize that is resistant to the Western corn rootworm (Diabrotica virgifera virgifera), eight with the isogenic strain and eight each with two conventional varieties. This enables researchers to compare the occurrence of individual insect species in the different variants, for instance. The different varieties have been distributed randomly, although plots of the same variety have not been located next to one another and the same number of each variety can be found on the field margin and in the middle.

With the unsettled weather this summer, the trial field looks completely different to last year, when the long heat wave affected the maize. This year the plants are considerably bigger and look much healthier. The different varieties are flowering virtually simultaneously and not one after the other, as was the case last year and as is supposed to happen. The genetically modified Bt maize and the isogenic variety, i.e. the parent variety without the genetic modification, are just beginning to flower, whilst the other varieties, including the buffer planting, are already in full flower.

A pit trap has been placed in each plot to determine the abundance of above-ground predatory arthropods in Bt maize compared with conventional varieties.

Here a trap filled with collecting fluid is emptied over an old tea strainer. The yield here too is very scant today; the trap contained just one solitary beetle.

Another researcher is working on the male flowers. He is collecting the anthers from two maize plants per plot using a home-made trap. He pulls the male flowers at the tip of the plants down towards him and shakes them into a plastic tube. At the end of the tube is a small glass jar in which the anthers together with pollen and insects are collected.

Even this collection method produces a low yield this year. This sample contains just two thrips and two Orius bugs. Last year a sample like this would have yielded as many as two hundred thrips.

On the other hand, there are more harlequin ladybirds around this year. This ladybird comes from Asia and is a bit larger than our common seven-spotted ladybird. What's more, it is not averse to consuming the larvae of the native ladybird, and could eradicate the seven-spotted ladybird over time. In the USA it has already ousted the once common ladybirds.