Situation of Diabrotica virgifera in the EPPO region: first reports in Bulgaria and Montenegro (YU)
The situation of Diabrotica virgifera (EPPO A2 quarantine pest) in Central Europe was reviewed during the meeting of the ad hoc Panel on Diabrotica virgifera held jointly with the IWGO International Workshop (Rogaëka Slatina, SI, 1998-11-27/28). In summary, the spread of D. virgifera continues in Central Europe but at a slower pace than was observed in previous years. Nevertheless, the numbers of adults trapped in all infested countries indicate that population densities are increasing. As in previous years, except in the parts of Serbia where the pest was first found, no economic damage has yet been seen on maize. But the numbers of insects caught in some parts of Romania or Croatia (close to the area in Serbia where economic damage are seen) tend to suggest that economic damage may be expected in the near future. New features in the spread of D. virgifera are its first records in Bulgaria and Montenegro (YU), and indeed the capture of 7 adults in Italy (see EPPO RS 98/161), which represents a major 'jump' of the insect towards the western European countries. Extracts from the report of the meeting are presented below.
44 pheromone traps have been placed along the borders with Slovenia and Hungary and all gave negative results.
Bosnia ; Herzegovina
In Bosnia ; Herzegovina, maize is an important crop covering approximately 200.000-250.000 ha, mainly in the north and north-east parts of the country. D. virgifera was first found in 1997 in areas bordering Serbia and Croatia. In the Federation of Bosnia ; Herzegovina, a survey on D. virgifera was initiated in July 1998 using pheromone and yellow sticky traps in the cantons of Posavina, Tuzla-Podrinje (which are situated in the north near the borders of Croatia and Serbia) and of Una (western part). D. virgifera was only trapped in the cantons of Posavina and Tuzla-Podrinje. The pest was found in the region around Tuzla (near Doboj, Gracanica and around Zvornik) and in the north along the river Sava (near Orasje). Populations have increased compared to last year and particularly in the region near the river Sava (border with Croatia). It is felt that D. virgifera is spreading along rivers and roads, from eastern and northern parts towards the centre of the country. No larval damage has been seen. Minor damage caused by adults on maize silks has been observed near Orasje (along river Sava).
In the Serbian areas of Bosnia ; Herzegovina in 1998, traps were placed near the following localities: Bijeljina, Zvornik, Br¹ko, Pelagicevo, Doboj and Banjaluka. In total, 2858 adults were caught. The greatest numbers were found in the eastern part (Bijeljina, Br¹ko). Only one adult was found in a single locality near Banjaluka. It is felt that the insect is spreading more rapidly along the river Sava towards the west than southwards. Considering the numbers of insects caught in the eastern part, it is supposed that populations have probably reached the economic level, however no indication of damage was given.
Maize is an important crop in Bulgaria and it is grown particularly in the north of the country. In 1987, 480.000 ha of maize was grown. After the first IWGO Workshop in Graz (AT) in 1995, a trapping programme was initiated in Bulgaria. Cucurbitacin traps were used in 1995 and 1996, and pheromone traps were used in 1997. Field inspections were also carried out. During the period 1995-1997, results were all negative. In 1998, 220 pheromone traps and 180 yellow sticky traps were placed along the northern and western borders of Bulgaria. Traps were inspected once or twice a week. The first three adults of D. virgifera were trapped on August 7th (the last one was caught in September 30th). In total 156 adults were caught. The insects were found in the north-west near the borders with Serbia (YU) and Romania (along the Danube). The highest numbers of insects were caught near Bregovo. It is estimated that the infested surface in 1998 is 200 km2. This is the first report of D. virgifera in Bulgaria.
D. virgifera was first found in the east of Croatia in 1995. One adult was caught in a cucurbitacin trap, but now it is considered that the pest was probably already present on an area extending about 30 km from the Yugoslav border and situated to the south of the river Bosut. In 1996, the pest spread westwards (80 km from the Yugoslav border) and adults were trapped in approximately 6000 km². In 1997, the area where adults were trapped reached 9000 km² and the front line of the outbreak was situated 100 km from the Yugoslav border. In 1998, pairs of pheromone and yellow sticky traps were placed at 138 sites. 64 sites were located in previously infested land, 37 along the line of spread (according to 1997 data) and 37 deep in the non-infested area. Monitoring started on June 25th , the first catch was made in June 26th and the last in September 21st. A total of 3368 beetles was caught (but this number is likely to increase as all data is not available yet). It is felt that the increase in population density in 1998 compared with 1997 is approximately 1.3. In 1998, D. virgifera spread towards the west (found in two new localities Nova Gradiëka and Gornji Varoë) and over a distance of 37 km along the river Sava (up to the village Gornji Varoë, situated at 150 km from the Yugoslav border and 150 km from Slovenia). In the middle part of the front line (in the middle of Croatia), D. virgifera spread only 8 km to the west. In the northern part of Croatia, along the border with Hungary, no further spread was observed. In the north of Croatia, there is a marshland area (Kopa¹ki Rit) near Hungary were beetles have been found for the first time in 1998. This marshland may have slowed down the spread of D. virgifera but it has not prevented it. At present, it is estimated that D. virgifera can be trapped in an area of approximately 9.500 km2 (in which 200.000 ha of maize are grown). In 1998, damage on maize roots was assessed in Otok (Slavonia, east of Croatia near Serbia). In an untreated plot the average damage rated 3 (using a scale from 1 to 9). However, no impact was seen on yield. It must be stressed that in Croatia no economic damage has been observed in 1998.
D. virgifera was first found in Hungary in 1995 in the south of the country. In 1997, D. virgifera spread towards the north (up to 100-120 km from the Yugoslav border). In 1996-1997, it was estimated that the pest has moved 40 km to the north and that approximately 10;000 km² were potentially infested by D. virgifera. The pest was present in the following counties: Baranya (Villány, Boly), Bács-Kiskun (Kecskemét), Csongrád (Szeged, Csanádpalota, Maroslele-Makó) and Békes (Mezökovacsháza, Mezöhegyes, Battonya, Csnádapáca). The highest population numbers were found in Békes and Czongrád counties. Larvae were seen for the first time, slightly damaging maize roots near Szeged (Czongrád county), but without any impact on maize yield. In 1998, the monitoring programme was carried out in infested areas, non-infested areas (according to 1997 results) and along the front line of the spread. It showed that the spread was very slow in 1998 but that populations increased. Increase of populations was registered in the following areas: Baranya (Villány, Boly), Bács-Kiskun (Kunbaja, Bácsalmás), Csongrád (Szeged, Csanádpalota, Nagylak) and Békes (Mezöhegyes). In the area of Szeged, slight larval damage was observed but no impact on yield was recorded. D. virgifera did not spread towards the north in 1998 (the front line is still approximately at 120 km from the Yugoslav border), but it has slowly moved towards the west.
Following the establishment and spread of D. virgifera in Yugoslavia, an alert programme was set up in Italy in order to be able to take containment and eradication measures as soon as the pest is found. A monitoring programme was set up in the north-eastern part of Italy with 12 trapping sites in 1997 and 20 sites in 1998 (1 to 10 pheromone traps per site). Maize field were selected in regions where maize is often grown continuously and also near potential points of entry (airports, firms trading with infested countries etc.). In 1997, no D. virgifera was found. In 1998, the first 7 specimens of D. virgifera were trapped between 21st July and 13th August in maize fields in Tessera, near the international airport of Venezia (Marco Polo). 3 adults were caught in one trap and the others in 4 separate traps. The shortest distance from the trapping sites to the airport was 500 m. Measures have been applied to try to eradicate or prevent the spread of the pest. In the area where D. virgifera has been found (1000 ha) and in its surroundings (5-10 km around the focus), a trapping grid (1 km x 1 km) will be set up and treatments will be applied if D. virgifera is found (however, it must be noted that no registered products are available), and the continuous cropping of maize will be prohibited. 10 km beyond this first trapping area, another trapping grid (5 km x 5 km) will also be established. In addition, it is prohibited to move fresh parts of maize and soil from the infested area. This is the first report of D. virgifera in Italy (see EPPO RS 98/161). It is unexpected in the sense that, if the pest is spreading westward from the outbreak in the Danube basin, it would have been expected to occur first in Slovenia, Austria or western Croatia. In fact, the origin of this introduction is not known. Air-borne transport from USA or road-borne transport from the Danube basin are both possibilities.
The first find of D. virgifera was made in 1996 at Nadlac (district of Arad – west of the country near Hungary) on yellow sticky traps. In 1997, D. virgifera was caught mostly in Arad, Timis, Caras-Severin and Mehedinti districts and it was estimated that an area of approximately 10000 km² was potentially infested. In 1998, the monitoring programme started in June 25th in 11 districts on 240 trapping sites (each site having both pheromone and yellow sticky traps). Insects were caught in small numbers in two new districts: Bihor and Hunedoara, showing that the pest still continues to spread towards the east, and north-east, particularly along the rivers Mureê, Dun²rea (Danube) and Timiê. It is estimated that an area of approximately 12000 km² is potentially infested. Increase in population densities has been recorded. Although it was noted that in some areas the numbers of adults caught were approaching the economic thresholds (according to US experience), no economic damage has yet been observed in Romania.
In 1998, 37 traps were placed along the border with Hungary and no D. virgifera were caught.
A monitoring programme has been in place in Slovenia since 1995 in the north-east and south-east of the country, which are two intensive maize-growing areas near Hungary and Croatia. So far, D. virgifera has not been found in Slovenia. Due to the findings in Italy, the monitoring programme will be intensified next year.
It must be recalled that D. virgifera was reported for the first time in Europe in Sur¹in, near Belgrade airport in 1992-1993. By using 900 pheromone traps, it was observed in 1998 that D. virgifera continues to spread towards the south. It is estimated that in Serbia the infested area was respectively: 0.5 ha in 1992, 6 ha in 1993, 60 ha in 1994, 275 ha in 1995, 10.787 ha in 1996, 15.695 ha in 1997 and 21.230 ha in 1998. However, damage was only reported near Belgrade, Pozarevac, Novi Sad, and Vrëac. This area has increased since last year and is now extending towards the borders with Croatia (on the west) and Romania (on the east). It is estimated that the area on which damage is observed covers approximately 10.000 ha. Results of surveys done in southern Backa (region around Novi Sad) showed that populations levels are still increasing. High infestations occurred in the eastern part of southern Backa as in 1997, and differences previously observed between the east and west parts of this region tend to disappear. Symptoms in maize fields were visible ("gooseneck" symptoms).
It is important to note that D. virgifera has now been found for the first time in Montenegro. A few adults have been trapped at three localities (near Bijelo Polje in the north of Montenegro) along a railway track.
EPPO Secretariat, 1998-11.