Aug 13, 2002

Research Live

Send

Research live series Part 2: A year in the trial field

Bt maize and arthropods: The time of the ‘pollen eaters’

It is early August 2002. The maize field has become a forest - the plants have shot up almost a metre in the last three weeks, despite the rain. They are taller than a man and in full flower.

Maize tassels with maize pollen

The male flowers are situated at the top of the plant and supply the pollen. A single inflorescence can strew several million pollen grains.

Female flowers with sticky silk-like filaments that catch the pollen

The female flowers are on the sides of the stems and encased in leaves. They form long sticky silks, which protrude beyond the leaves and catch the pollen. It is the female flower-heads that later produce the infructescence – the maize cobs.

René Mause measuring the maize plants

The male panicles are shaken to collect the pollen sacks and the yellow pollen.

Jörg Eckert uses this ‘inverted umbrella’ to collect ‘pollen eaters’.

Corn borer hole

European corn borer larva in the stem of a maize plant

The larva has eaten its way into the stem.

European corn borer larva on a maize leaf

The caterpillar determinedly works its way back towards the stem

There is no one in sight, only a gentle rustling betrays the fact that there is someone in the field.

The forest parts and project leader Achim Gathmann appears at the edge of the field covered in yellow pollen and holding a large jar in his hand. “For collecting pollen”, he explains.

The ground has been softened by all the rain, and more rain is in the air. This means that the pollen doesn’t fly quite so well, but even in this weather you just need to stroke the maize plants for clouds of pollen dust to come trickling down.

Standard for maize plants

Today, like every week, the growth of the maize plants is recorded. This is done so that the samples can be identified later on. Three plants per plot are selected – those which are furthest developed. First the height is measured: 2.35 metres. The development stages are described, identified and given a number using a standard table – the BBCH scale for dicotyledonous plants.

“According to the table, we are now at development stage 65”, explains René Mause, a project worker.

65 means that the male flower-heads are in full bloom, i.e. top and bottom panicle branches are flowering and the silks of the female flowers are fully formed.

Collecting pollen and ‘pollen eaters’

Since the maize started flowering, the project team has had a few new tasks in addition to emptying traps and scoring selected plants.

Now they are collecting pollen, both from the Bt maize and from the isogenic control plants, i.e. from the same variety without genetic modification. The male panicles are held inside a glass and shaken. The collected pollen is frozen. It will be used later for laboratory tests, e.g. feeding experiments with caterpillars.

The flower-visiting insects are also recorded during the flowering phase. These are mainly ‘pollen eaters’. They too are shaken from the male flowers of individual plants with the help of an ‘inverted umbrella’ or funnel. The project team made this ‘high-tech’ device themselves. It consists of the frame of an old kitchen sieve, a plastic bag and lots of sticky tape. Right at the bottom there is a small glass, in which the insects land after the shaking procedure. This device is used twice during the flowering period on five sites per plot and on five plants at each site.

Waiting for the corn borer

Isolated corn borer holes are already visible. The European corn borer bores into the stem at the top, where the plant is soft and nourishing and then eats its way down the plant. The borehole it makes is a weak spot for the plant, making it susceptible to pathogens. And eventually the stem will snap.

More from GMO Safety