M. BERTOSSA
Swiss Federal Research Station for Plant Production, Centre of Cadenazzo, Switzerland
J. DERRON
Swiss Federal Research Station for Plant Production, Changins-Nyon, Switzerland
L. COLOMBI, R. BRUNETTI
Phytosanitary Service Canton of Ticino, Bellinzona, Switzerland

After detecting four (4) western corn rootworm (WCR) adults on sex pheromone traps (Csalomon^®) near the airport of Lugano-Agno in 2000, measures were taken to eradicate the supposed hazard to maize within the region. It was easy to believe that this infestation occurred at this location since flights into the Lugano Airport from Serbia took place in the early summer 2000.

METHODS
The measures that have been taken as a result of 2000 WCR catches, among others, was the use of an increased number of traps for 2001. A total of 74 traps were placed in 37 selected sites of the Swiss territory: 10 sites in the German part, 13 in the French section, and 14 in the Italian part (Ticino), including the Lugano Airport site. The traps were primarily placed along the main transportation routes in the main maize growing regions. Ticino is a territory that accounts for about 1200 ha of maize in small structured fields. The topography of Ticino shows three distinguishable maize regions, each separated by mountains and lakes. These include the border region in the south, hereinafter called Zone A; the Lugano region in the middle, Zone B; and the Magadino plain region 40 km northward, Zone C. All the traps were attached to a stake and placed approximately at ear height. They were set out in pairs within 20 m distance of each other near the edge of maize fields. The traps were monitored once per week from the 5^th July until the end of September, with the pheromone being changed every 30 days, or 2 times for the sampling period (except 2 sites with a third exchange).

RESULTS
Italian part of Switzerland: Ticino
Zone A:
in the four trapping sites during the 12-week trapping period, an average of 143 adults per week was found. The first beetles were observed the 5^th of July. a total of 1710 insects were trapped with 75 % coming from one  maize field. the rest were equally distributed in the remaining locations and a relevant number of adults appeared there only 3 weeks later.
Zone B:
During the same period, an average of 39 adults per week was found. However, catch numbers for July were not significant. The main flight period occurred within the August 2^nd and 22^nd time period with an average of 108 beetles trapped per week. A total of 462 WCR were captured. The distribution over all sites was almost equal.
Zone C:
Only 2 WCR beetles per week were trapped over the same monitoring period

French and German parts of Switzerland:
In the remaining 23 locations no WCR beetles were found over the 12 weeks.

CONCLUSIONS
The number of Diabrotica detected in 2001 would indicate that a population of WCR is established near the border zone of Chiasso. In the Lugano zone, where in 2000 the first specimens were found near the airport, it’s not clear whether an established resident population is involved. Time delay in appearance, number of trapped WCR in 2000 and 1999 near Lugano Airport, equal distribution between the locations, and crop rotation regulations that have been enacted indicate a possible migrant population. But there is no certainty that the traps were located at sites that would prove this.

The four adults captured in 2000 possibly have an origin other than arriving by airplane. They easily could have migrated by themselves from zone a or from the bordering area of Italy. As the most prolific trap is only few meters away from the border and very near to the main railway station, it is possible that the beetles arrived one or more years before 2000 and became established in the region. In the maize field where beetles were first captured, which has a surface area of one hectare, maize has been grown five times in eight years with 2 interruptions.

For next year, authorities have decided to forbid the growing of maize in the same field in Zones A and B. The transport of silage from Zones A and B to C are also forbidden. An eradication strategy seems inappropriate since the insect is well established in Northwestern Italy and would serve as a source for reintroduction of WCR no matter the steps taken by Switzerland to eradicate it.