Peter BAUFELD
Federal Biological Research Center for Agriculture and Forestry, Stahnsdorfer Damm 81, 14532 Kleinmachnow, Germany

Diabrotica virgifera virgifera is the most serious insect pest on maize in the USA and Canada and causes considerable crop losses. The non-native leaf beetle was introduced into South-East Europe at the beginning of the 90ies and has continuously spread since than. Therefore, it is to be expected that the pest will reach further European maize-producing areas like Germany, too.

The Western Corn Rootworm would find maize in all regions of Germany, but the most endangered areas are those with the highest maize concentration. We assume that regions with more than 50% of arable land in maize have significant areas in continuous maize and defined these areas as "maize areas with high risk". The production of continuous maize is the best precondition for rapid development of maize rootworm populations and results in a high establishment potential and crop losses.

In Germany, in the four federal lands of Niedersachsen, Nordrhein-Westfalen, Bayern and Baden-Württemberg there is a high frequency of continuous maize. About 348,000 ha of maize (130,000 ha grain maize, 218,000 ha silage maize) in Germany are under high risk for Western Corn Rootworm infestation. This area amounted to one third of the maize production area of the four above mentioned federal lands and more than one fifth of the whole maize production area of Germany in 1995. The long-term experience of insecticide use in Canada (Ontario), supports the assumption that Germany has a potential for up to 111,000 ha treated with rootworm insecticide annually at an added insecticide (Counter SG, terbufos) cost of 25 million DM per annum. Without crop rotation, rootworm infestations could cost German maize producers 49 million DM in crop losses each year. Experience from Canada supports the strategy of changing crop rotation away from continuous maize to reduce the potential for the establishment of western corn rootworm, the potential for economic loss, and increased application of insecticides.