P. BAUFELD
Department for National and International Plant Health
S. ENZIAN
Institute for Technology Assessment in Plant Protection, Federal Biological Research Centre for Agriculture and Forestry, Stahnsdorfer Damm 81; 14532 Kleinmachnow; Federal Republic of Germany

The dispersal rate of the Western corn rootworm (WCR) in Europe was analyzed starting with the introduction to Serbia in the beginning of the 90ies. The dispersal rates of the WCR differed from year to year. The spreading of the WCR ranged from 60 to 100 km per year without and from 0 to 37 km with containment measures (FAO program TCP/RER/6712). The simulation model used as average a maximum spreading rate of the population of the WCR of 80 km per year without and of 20 km per year with containment measures. The maximum spreading rate is reached by WCR in the succeeding year only if continuous maize is available in the infested area. The concentration of maize in crop rotation is the main factor in the simulation model. In case of low maize concentration, the multiplication factor and spreading pressure are very low. In that case we reduced the spreading rate by a correction factor K which is defined as follows:

In case of >= 50 % of maize in crop rotation
K = 1 and
in case of < 50 % of maize in crop rotation
K = (concentration of maize in % x 2) : 100

The following formula was used in the simulation model to calculate the spreading rate of the
WCR: AR = FD x K
    where
    AR = spreading rate of the WCR
    FD = distance of flight with (20 km/year) or without containment measures (80 km/year)
    K = correction factor (see above)

Furthermore, the topography was analyzed in the infested areas of Southeast Europe. Analysis showed that the WCR is not able to fly over altitudes of 900 m, which was considered in the simulation model. The lowest mountain chain in western Europe is up to 800 m and has valleys (often with maize) which favor progressive dispersal.

All information is utilized in the simulation model on the spreading of the WCR. Calculations are carried out the basis of the GIS software ArcView/ArcInfo. This simulation model was used for the first time to simulate the spreading rate in Germany over ten years for two cases: Introduction via the international airport of Frankfurt am Main with and without containment measures and progression of „natural spread“ via Austria with the starting point in Passau (Southeast Bavaria on the Danube river at the border to Austria) with and without containment measures.

As a result of the simulation an infested area in case of  an introduction via Frankfurt am Main of  475.740 ha without and 23.107 ha with containment measures was calculated for a period of ten years. In the second case of „natural spread“ from Passau calculation gave 358.691 ha without and 118.419 ha with containment measures for the same period.