Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Potential risk of WCR (Western Corn Rootworm) establishment in selected EU countries

Temperature is one of the most important factors for the establishment of the WCR (Western Corn Rootworm). Egg mortality depends on winter temperature and could reach 50% at -10°C for four weeks and at -15°C for one week. Infested areas in the USA show great differences in January long-term mean temperatures. January long-term mean temperatures range from 4.4 to -14.1°C and reach an average of -4.8°C. The coldest January long-term mean temperatures, up to -14.1°C, are registered in the USA in North Dakota where the WCR is established.

The above-mentioned temperatures are air temperatures and the eggs over wintering in soil at a depth of 15 to 30cm, in these regions probably at 30 cm or more. For Germany for example, January long-term mean temperatures range from 2.8 to -3.8°C and are on average -0.5°C. A comparison of winter conditions between the USA and Germany concluded that winter conditions are not the limiting factor. Furthermore, the WCR is established in Canada (Ontario and Quebec) where cold winters are common. In Western Europe, long-term winter temperatures are not as cold as in most part of the USA and of Canada because Western Europe is influenced by maritime climatic conditions. Winter conditions in Western Europe are not the limiting factor for establishment.

Temperatures in the growing season are responsible for the successful finishing of a generation, increase of population and finally the establishment of the species. Because this species is more adapted to continental climate with hot summer time in the growing season, this season has a stronger influence on the development, abundance and finally on the damage potential of WCR.

There are great differences in the calculated development time of the single stages of WCR between the southern (e. g. Italy), and northern countries (e. g. the Netherlands and Germany) considered. In Italy, development conditions are good because of the warmer temperatures in the growing season. In the temperature sum model, the first 50% of egg hatching would be expected on 24th of April in the south and in average on 28th of May for Italy. But in the south, there could be a mortality in the development of eggs because of lower temperatures for diapause are missing. On the other hand, maize growing in the south of Italy is not so important as in the north with high maize concentration areas (e. g. Lombardia, Piemonte and Veneto).

In contrast to Italy, the model calculated for the Netherlands and Germany averaged 50% egg hatching for 10th of July beginning on 5th of July and 20th of June and ending on 20th of July and 30th of July, respectively. In France, the emergence of 50% of first instar has a wide range from 21st of May in the south to 25th of July in the north. The third instar as the most damaging stage of WCR is expected to hatch between 16th of June in Italy and 29th of July in the Netherlands. The earliest emergence for the third instar was calculated for the south of Italy (14th of April) and latest for the north of Germany (28th of August). Beside Italy (14th of May to 27th of July), France would cover a wide range from 11th of June in south to 19th of August in the north. For the emergence of the short pupa stage the relations would be the same (e. g. France).

First adults of WCR would appear in Italy between 27th of May and 10th of August and on average on 28th of June. In Italy, with optimal climatic conditions for the development of WCR, there exist first data for the catching of adults in pheromone traps from 2001.

In contrast to Italy, in Germany the adults would appear between 16th of July and 7th of October and on average on 10th August. In the Rhine valley (Southwest of Germany, federal land Baden-Wurttemberg), there are also favourable conditions for development in the growing season and in addition a high concentration of maize. In this area the development of high abundance and economic loss is probable. In the north of Germany (e. g. federal land Schleswig-Holstein), hatching of the beetle would be very late so that the conditions for feeding and egg laying already would be unfavourable. In extremely cold years in the north of Germany (Flensburg), populations would not be able to finish the generation. The north of Germany (Flensburg region) and furthermore Denmark could form the climatic barrier to build up a damaging abundance of WCR.

In France, which has a wide temperature spectrum from Mediterranean to moderate climate, the emergence of the adult beetle would range from 23rd of June to 9th of September. With the exception of some unfavourable areas where maize growing is not favoured, most areas of France provide good conditions for the development of WCR as do Austria, Switzerland and Luxembourg, too. In the Netherlands and Belgium not optimal conditions for WCR development are expected.

Reported by

Biologische Bundesanstalt fur Land- und Forstwirtschaft
Stahnsdorfer Damm 81
14532 Kleinmachnow
Germany
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