Lorenzo FURLAN⁽¹⁾ , Marco VETTORAZZO⁽²⁾, Carlo FRAUSIN⁽³⁾, Lanfranco DONANTONI⁽⁴⁾, Alessandra GOMIERO^(4)
1 Institute of Agricultural Entomology, University of Padova Agripolis, Via Romea 16, LEGNARO PD; Italy
² Phytosanitary Service of Veneto, Venice Office, via Poerio 34, 30173 MESTRE VE; Italy
³ Phytosanitary Service of Pordenone, via B. Odorico 13, PORDENONE; Italy
⁴ Phytosanitary Service of Veneto, Venice Office, freelance

Abstract:
Due to the discovery of the first specimens of Diabrotica virgifera virgifera Le Conte near the International Airport of Venice in 1998, an attempt to eradicate or at least to contain the newly arrived population was implemented by using different strategies in 1999. The methods chosen and the first results are reported.

HISTORY AND PLANNED STRATEGIES
After it was clear that Diabrotica virgifera virgifera Le Conte (WCR) had started to spread quickly from Serbia to the surrounding European countries, a monitoring program has been in action in the north-eastern part of Italy since 1995 by using chromotropic traps in the first years, sex pheromone traps in 1997 and 1998. Maize fields were selected in areas where maize is often grown for multiple years and also in potential introduction areas (such as near airports, customs areas, etc.). In 1998 the first 7 specimens of WCR were trapped in Tessera, a site near the Marco Polo International Airport in Venice (Furlan et al.., 1998). Since possible future WCR damage to maize cultivation’s in Italy might be caused by:
a) the establishment of a conspicuous population in the area where the first specimens were captured and the species spreading widely from this area to the surrounding ones,
b) further accidental introduction from regions where high populations are already present (eastern Europe countries, USA);
c) progressive natural expansion of WCR populations to north-eastern Italy from eastern Europe;
the immediate-implementation of eradication and protection strategies was considered essential. First of all it was proposed that a focus area be identified (1100 ha) where the species is present and a safety area be defined just around the focus area (extending 7 - 14 km from the border of the latter, 35.000 ha wide). In order to decrease the likelihood of successful mating and, as a consequence, of egg laying we suggested that maize monoculture be prohibited in the focus area and that treatments be applied against the adults in the focus area and in the safety area too, just around traps which possibly would have captured specimens. In fact, corn monoculture proved to be the key factor in allowing WCR populations to increase in Europe (Camprag et al., 1998) as it was observed in USA. Experiments carried out in the USA have shown that significant reductions in adult populations (close to 100%) can be obtained by implementing post-emergency insecticide treatments against the adults (Chandler and Sutter, 1997; Chandler, 1998). On the contrary, soil insecticides proved to be of no or little effectiveness for reducing WCR population levels despite the fact that they can be useful in decreasing root damage where high larval populations occur (Sutter et al., 1991; Gray et al., 1992). The proposed strategy can be synthesized as follows:

FOCUS AREA: with presence of WCR in 1998 plus 1 - 2 km beyond

• population monitoring by using sex pheromone traps (trapping grid 0,5 km X 0,5 km)
• 1 or more adults caught:
  treatment of all the maize within the area; if no adults were captured early in the season in any case treatments should start in the beginning of July;
• continuous maize cultivation prohibited;

SAFETY AREA: 5 - 10 km beyond focus area

• population monitoring by using sex pheromone traps (trapping grid at least 1 km X 1 km)
• 1 or more adults caught:
  treatment of maize fields within 1 km from the trap
  addition of sex pheromone traps further away and continuation of the procedure as above.

IMPLEMENTATION
a)Eradication program: it was implemented thanks to a specific Ordinance of the Veneto region based on:

• prohibition to plant maize in the fields where corn was cultivated in 1998: taking into account the documents supplied by the farmers to receive EU aid for cultivation, all the .fields which had been planted with maize in 1998 in the focus area were identified. For small fields specific inspections were carried out. The owners of these fields were informed about the prohibition of planting maize again. By May 1999 all the fields planted with maize in 1998 were checked for the crop actually planted in 1999; out of 88 hectares, none were found to have been re-planted with maize. Most of the other fields were planted with soybeans. Farmer who decided to plant maize (about 3 5 hectares) as a second crop after barley or winter wheat sown in fall 1998 just after maize harvesting, were obliged to sow after July 5 , since by this date all WCR eggs should have hatched and the young larvae should have died not having found maize roots available;
• obligation to apply chemical treatment against WCR adults on corn: in order to have reliable information regarding adult swarming, 60 pheromone traps (Cloak type produced by the Plant Protection Institute of Budapest) were placed out in the maize fields of the focus area and 250 traps in, the maize fields of the safety area. New traps were added a few meters away from each of these traps after 45 days. All the maize fields were treated twice by using a bridge tractor; in the first phase, from July 12th to July 27th, fenithrothion was applied at the rate of 625 g / ha of a.i.; in the second phase, from August 1st to August 15th, Dursban 75 WG was sprayed at the rate of 825 g / ha of the a. i. chlorpyrifos. The shift to chlorpyrifos was decided because the product was registered for application against Diabrotica virgifera virgifera on maize crops (it is the only insecticide registered for Diabrotica in Italy so far). The first treatment began later than forecast due to technical problems with the sprayer. Since the trap which captured 2 males was located at the border of the focus area, 11 hectares of maize in the nearby safety area were also treated. Furthermore, the monitoring grid around this trap was thickened;
• prohibition to move fresh corn or soil in which corn was grown the previous year, outside the focus area;
• prohibition to thresh corn before October 1st (in order to avoid possible adult spreading);

RESULTS
Only 2 males of Diabrotica virgifera virgifera were captured despite the fact that 6 times more traps. were placed out in the focus area in 1999 than in 1998. The 2 males were trapped on July 6th and July 26th in the same trap set up few meters outside the western part of the Airport facilities. Therefore the eradication strategies implemented appear to have been really effective for controlling WCR populations. There was no increase in the number of males captured in comparison to 1998 and no spreading outside the focus area was observed.