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.

Diabrotica virgifera virgifera on South-Northern expansion drive?

As Wudtke and colleagues predicted and Hummel and colleagues later confirmed, the Western corn rootworm Diabrotica v. virgifera LeConte (Coleoptera: Chrysomelidae) (WCR) had shown the ability to expand northward from South and Eastern into Central Europe. Decades earlier WCR had done the same in North America. Yet, European entomologists erroneously assumed they would be somehow magically protected from such aggressive moves of WCR. Meanwhile we know better: Southern Germany is infested, and also many East European countries are victims of these Northern and also Eastern advances. In Germany, neither speed nor extent of such advances is well defined. Jumping advances similar to earlier spreading episodes may be the rule, but they are not well predictable. In this report, we argue for a persistent northbound trend of WCR.

Containment of the western corn rootworm Diabrotica v.virgifera: continued successful management 2008 in southern Switzerland by monitoring and crop rotation.

Diabrotica virgifera virgifera LeConte (Col.: Chrysomelidae), known as western corn rootworm (WCR) and endemic in North America, invaded Europe about two decades ago. Various unsuccessful attempts have been made to eradicate it from the Old World. Management with a variety of strategies is the option now remaining. WCR management in Southern Switzerland by a unique containment approach has been practiced successfully since 2003 using biotechnical means. Without any chemical pesticides or GMO input, the Swiss government mandated adherence to strict crop rotation. In addition to the economic benefits of this relatively simple approach, the environment was saved a considerable burden of pesticide applications. Other countries are invited to follow this example of sustainable pest management.

Experiences with population dynamics of Diabrotica virgifera virgifera LeConte in the Swiss canton of Ticino up to 2007.

The Western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is a vexing alien invasive insect pest. It occupies the attention of entomologists in most countries of Europe and beyond. In spite of numerous research advances (e.g., Diabrotica symposium at Engelberg, Switzerland 2004) its behavior is still incompletely understood and cannot be predicted for a specific growing season with any degree of certainty. Nonetheless, by comparing several years in sequence a somewhat consistent and coherent picture is emerging that is subject of this contribution. The Ticino province received first beetles from the major infestation in Lombardy in 2000 across the geographically open border at Chiasso. The rapid advance of WCR in northerly direction along the river valleys of Ticino and Misox posed a threat to cantons north of the mountain chain of the Alps and beyond, a scenario outlined by Bertossa (2004), Wudtke et al. (2005) and subsequent papers. Following the Swiss Federal rule of crop rotation obligation around infested regions introduced in 2001, the rapid increase in population density leveled off. Careful monitoring by both Metcalf type pheromone and kairomone baited sticky traps and Hungarian traps provided a reliable tool for judging the success of any quarantine measures taken up until 2007. (1) Trends in population development of 2006 were confirmed. (2) However, for reasons not well understood, the overall population encountered in 2007 was significantly smaller in Ticino and neighboring areas of Lombardy, Italy, but also in other areas south of the Alps. This may be a consequence of the rather mild winter 2006-2007. (3) At the mountain pass of Monte Ceneri (some 600 m above sea level) no beetles were trapped in 2007, while 3 WCR were seen in 2006. (4) No new WCR were encountered in Swiss cantons north of the main chain of the Alps. (5) Metcalf sticky traps proved to be 4-5 times as sensitive as Hungarian traps used for comparison. By and large, mandatory crop rotation was beneficial in reducing WCR populations in Ticino and avoided or delayed northbound spread of WCR.

Diabrotica virgifera virgifera in Switzerland: future invasion trend into Germany via transalpine, terrestrial routes.

The western corn rootworm Diabrotica v.virgifera (D.v.v.) (Coleoptera:Chrysomelidae) is endemic to the New World. On at least 3 occasions, it invaded Europe (Miller et al. 2005). The first of these invasions took place in or before 1992 (Baca 1993) to Belgrade, Serbia, and gave rise to a rapidly expanding beetle population in SE Europe. Its larvae are causing economic damage to Zea mays for the last ten years, with increasing severity both in acreage and density. Meanwhile Germany is still without proven infestations as of 2005, but is surrounded by countries invaded by D.v.v. It will be a matter of time and careful search efforts with efficient traps to detect D.v.v. on German territory as well. Three main terrestrial routes of future introduction are likely (Wudtke et al. 2005, Hummel et al. 2005 a and b; Baufeld and Enzian, 2005), one of them leading from Northern Italy through Southern and Northern Switzerland to Southwestern and Southern Germany.

The western corn rootworm diabrotica Virgifera virgifera en route to Germany.

The western corn rootworm Diabrotica virgifera virgifera LeConte (Col.:Chrysomelidae) (D.v.v.) is one of the most important maize pests in North America. Ever since its invasion into Europe and its detection near Belgrade airport by BACA in 1993 it quickly spread all over southeastern Europe and is now advancing towards central Europe. Up until summer 2004 considered free of D.v.v., Germany is, with the exception of its northern and northeastern borders, surrounded by countries with proven D.v.v. infestations. In addition to simultaneous spot introductions by airplanes, three main routes for terrestrial introduction into Germany are likely: 1. from south to north via Lombardy (Italy) through Switzerland to the State of Baden-Wuerttemberg in the southwest; 2. from south east to northwest via Croatia, Slovenia, Austria into the State of Bavaria; and 3. from Belgium and the Netherlands in southeasterly direction to the state of Northrhine-Westfalia. From these, progress of D.v.v. along route 1 is so far the most advanced. It follows the well established network of road and rail connections through Switzerland and underscores the active role mankind and its technology plays as an active distribution vector for D.v.v. Mandatory crop rotation in the Swiss Canton of Ticino did slow down but could not prevent the northbound advance of D.v.v. in 2004. Considering the recent discovery of D.v.vu near the South German border, its introduction into German territory is only a matter of time and may be ecologically unavoidable. In Slovenla, another relatively small southern transit state, the D.v.v. population density is still much lower than in Switzerland but with significantly increasing trend during 2004 and with special emphasis in its southeastern provinces. Considering its relatively short distance to southeastern Bavaria and the well developed transalpine rail, road and tunnel system, Slovenia as a transit state may provide another access route for D.v.v. of lesser but still significant importance to Germany.