Corn root worm

A new maize pest from North America

The Western corn rootworm is a 5-8 mm black and yellow beetle. In its native home in North America it is responsible for significant harvest losses, which has earned it the name "billion-dollar bug".

The Western corn rootworm was brought to Eastern Europe at the beginning of the 1990s; a few years later it spread to Western Europe. New infestations often occur in the vicinity of airports. Local infestations of the pest have been found near Paris, London, Brussels and Amsterdam. It has not yet been found in Germany.

The Western corn rootworm lays its eggs in the soil of maize fields in late summer. The larvae hatch in the following spring. They feed almost exclusively on maize roots. The beetle that hatches from the chrysalis in the summer eats the parts of the maize plant above the ground. While the larvae have a cruising radius of no more than one metre, the nocturnal beetles can cover about 20 kilometres.

To protect crops against infestation by the Western corn rootworm, whose larvae need maize for fodder, farmers in the USA introduced a two-year crop rotation with maize and soya. Now, however, beetle strains are emerging that will also lay their eggs in soya fields and others whose eggs can survive a two-year dormant period.

At the end of February 2003 a genetically modified maize line was approved in the USA which, like the familiar concept used to combat the European corn borer, produces a Bt toxin that has a specific effect on the Western corn rootworm. In Europe, genetically modified maize that is resistant to the Western corn rootworm is awaiting authorisation.