A visit to Thrips & Co.

"Over there", he points with his finger to a narrow strip of maize, which is already somewhat higher than the rest, "that’s a cordon of non-GM maize which we have planted in narrow strips between the individual plots and at the margin to help us find our way around."

There are 24 plots altogether, one field with fifteen plots and one with nine. Three different maize variants have been planted in these fields: transgenic Bt maize; the so-called isogenic parent strain, that is the same variety but without genetic modification; and in addition the isogenic strain sprayed with insecticide.

Each of the three variants is repeated eight times and the plots are distributed over the fields in a specific grid pattern. This is known as a trial layout.

The aim of the research project at this stage is to establish whether the arthropod population varies between the different maize variants.

Are there fewer, more or the same number of flower visitors and aphid eaters on the Bt maize plots? And does the composition of the species community change?

The current phase of the project basically entails working on site emptying the traps so that their contents can be analysed in the laboratory.

There are also four plants in each plot which are used for the scoring system, i.e. at least once every two weeks, aphids and other creatures are counted and identified in situ on these same four plants.

These plants have a ribbon attached to them and are always positioned on the diagonal according to a specific pattern or row-counting formula. Only experienced field workers can find their way around here.

Life can be hazardous in the maize field

It is easy to walk around the maize field without damaging the plants. There is plenty of room between the stalks. Achim Gathmann makes a beeline for the first trap, a yellow pan.

There is one yellow pan in the middle of each plot. Attracted by the yellow colour, a vast number of small and even smaller creatures have fallen into the trap. They are swimming in ethylene glycol, a preservative, which is then strained through a sieve to empty the trap. Tweezers are then used to transfer the contents of the sieve to a glass tube containing 70 percent ethanol. And hey presto, the glutinous mass has turned back into recognisable insects. Then the sieve is rinsed again to make sure none of the tiny thrips get left behind, such as storm bugs, which are a mere 2 millimetres in length.

We move on to the next trap. A hole in the ground with a container in it and a small roof over it to keep the rain out. These pit traps do not use scent or colour to attract the insects; they just fall in as they are walking past, as it were. The pit traps are filled with the same liquid as the yellow pans.

And finally the frame traps. These are quite large, about a metre square, and covered with a type of gauze. They are used to trap insects coming from the soil to the surface. When they try to get out of the frame, they always run along the edge, so there is a pit trap in each corner of the frame. These traps are designed mainly for spiders and ground beetles.

The traps are emptied every week. There is one yellow pan, a frame trap and two pit traps per plot and 24 plots, making a total of 96 traps to empty.

"In situ species identification"

Since a maize field harbours about a thousand different species of arthropod, it is obvious that only a small number of them can be counted, identified and observed. The various herbivores are interesting, for example the thrips, which are known as a Fransenflügler or fringe-winged flies in German, of which there are about ten different species. And of course the three or four different species of aphid and some of their antagonists such as hover flies, ladybirds and green lacewing larvae, also known as aphid lions.

In situ species identification, Gathmann explains, is ‘scientific speak’ and means finding and identifying species on site.

Every now and then there are small, open strips in the maize field. These are weed strips sown with yellow mustard and goosefoot to provide fodder plants for different species of caterpillar. A further aim of the project is to study whether Bt maize has an effect on caterpillars in adjacent weeds.