Cultural diabrotica containment strategy in Switzerland: until now a convincing success story

Ever since 2000 Switzerland belongs to the 22 European countries where the quarantine pest Diabrotica virgifera virgifera LeConte, Western corn rootworm (WCR), has been detected. It is reported to be the most important maizepest worldwide with an economic damage reaching 1.5 billion US$. In Switzerland it is constantly present in the southern part of the Alps while only few beetles are sporadically found in the northern part. Observations from 2000 up to 2012 support the hypothesis that the populations in the southern part of the Alps are generated by yearly migrations from principal foci situated in neighbouring Italian areas of Lombardy. Neither the tight correlation between travel distance and time of first arrival at various points from South to North, nor the steady decline of population along the route can be explained otherwise. Control measures enacted by Swiss authorities were principally based on a tightly enforced crop rotation scheme without chemical inputs as usually practiced in parts of the European Union. The effectiveness of crop rotation has been tested in a 5 year field trial comparing a continuous maize cropping system with a croprotation system and a maximum of one year of maizewithin a two year period (1:1). Population density was measured using synthetic pheromone baited traps and observations of root damage. Results showed that no economically relevant population built up during this period in the crop rotation treatment, whereas in the statistical evaluation of continuous maizecropping root damages could be detected after 4 years. One to one (1:1) year crop rotations are a common practice since 2001 in Southern Switzerland and are well accepted by farmers. Consequently, not a gram of pesticide has been employed against WCR in Switzerland up to now. The low level population density also helped to avoid the introduction of WCR populations into Cantons north of the Alps and thus prevented further spreading towards the state territories of northern neighbours.