Present situation of Diabrotica virgifera in Central Europe
The situation of Diabrotica virgifera in Central Europe was reviewed during the joint meeting of the 2nd EPPO ad hoc Panel and 4th International IWGO Workshop which took place in Gödöllo (HU) on 1997-10-29/30. In short, the spread of Diabrotica virgifera (EPPO A2 quarantine pest) continues in Central Europe at a rather rapid pace, adults being trapped over a wider and wider area. However, except in the parts of Serbia where the pest was first found, no economic damage has yet been seen on maize. Because the adults can fly considerable distances, it is difficult to decide which parts of the ‘potentially infested’ areas where adults are trapped in fact contain breeding populations.
An FAO project has been set up to monitor the spread of D. virgifera by placing traps in several countries (including some permanent trapping points), and also to try to control and contain the pest by intense trapping and area-wide management (aerial treatments with SLAM® : bait + insecticide (carbaryl).
A survey on D. virgifera was initiated in July 1997 using pheromone traps in the cantons of Tuzla-Posavina and Zenica-Doboj which are situated in the region near the borders of Croatia and Serbia (Yugoslavia). D. virgifera was trapped in the region around Tuzla (but the situation towards the west where the pest is progressing, or toward the south, is not exactly known). This report confirms earlier records of D. virgifera in Bosnia-Herzegovina.
D. virgifera was first found in the east part of Croatia in 1995 (EPPO RS 95/005). 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 (EPPO RS 97/033). In 1997, many traps (both yellow sticky traps and pheromone traps) were placed in this area, along its border line and at the west of it. Approximately 3500 beetles were trapped from July to October 1997 (mainly in pheromone traps). The area where adults are trapped has now reached 9000 km² and the front line of the outbreak is situated 100 km from the Yugoslav border. Larval damage to maize roots was seen in an insecticide trial (root damage was rated at 5 on a scale from 1 to 9), but no yield reduction on maize was noted.
D. virgifera was first found in Hungary in 1995 (EPPO RS 95/157) in the south of the country. As in previous years, the monitoring programme continued in 1997. The results showed that D. virgifera continues to spread towards the north (up to 100-120 km from the Yugoslav border). In 1996-1997, it is estimated that the pest has moved 40 km to the north. More than 4000 beetles were caught in pheromone traps. The pest is now 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 general, populations are more abundant in places where maize is grown as a monoculture. It is estimated that approximately 10 000 km² are now potentially infested by D. virgifera in Hungary, and it is expected that the pest will continue its progression towards the north of the country. In southern Hungary, aerial treatments on wide areas have been initiated using Slam®(a commercial product which contains a bait and carbaryl in a special formulation).
The first find of D. virgifera was made in 1996 (EPPO RS 96/165) in Nadlac (district of Arad – west of the country near Hungary) on yellow sticky traps. In 1997, a monitoring programme started in July with 240 pheromone traps located in the western part of the country (Arad, Timis, Caras-Severin, Bihor). In August, more traps (pheromone and yellow sticky traps) were placed in four other districts (Mehedinti, Alba, Hunedoara and Dolj). Approximately, 40000 adults have been trapped in Romania. D. virgifera was caught mostly in Arad, Timis and Caras-Severin districts. In August and September, adults started to be caught in Mehedinti district which is situated near Bulgaria. The present situation in Bulgaria is not known. In Romania, it is estimated that approximately 10000 km² are now potentially infested, but no root damage was seen. No insects were trapped in the other districts studied (Alba, Bihor, Dolj, and Hunedoara).
It must be recalled that D. virgifera was reported for the first time in Europe in Surcin, near Belgrade airport in 1992-1993 (EPPO RS 94/001 and 94/062). A monitoring programme was done in 1997 and showed that the pest continues to spread towards the south of Serbia, as it can now be found in places near Kragujevac. 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, and 10 787 ha in 1996. It is felt that the total potentially infested area in 1997 has been multiplied by 2 compared to 1996. However, damage was only reported near Belgrade, Pozarevac and Vrsac (an area of 50 km from south to north and 130 km from west to east around Belgrade). Damage in 1997 was not as severe as in 1996, as with abundant rains in summer, maize plants were able to recover. The pest has not been found in Montenegro.
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.
Surveys will continue in countries where the pest is present and in neighbouring countries. During the meeting, it was pointed out that pheromone traps are probably the best available tool to follow the progression of the pest, whereas yellow sticky traps are to be used in places where the pest has been present for a sufficient time to reach a certain population level. Many studies are being done on the efficacy on plant protection products applied as soil treatments against larvae or aerial treatments against the adults, and the establishment of control strategies. Finally, pest risk analysis studies on D. virgifera are being carried out, and as an oversimplification it may be suggested that wherever maize can be grown in Europe, the pest is likely to survive and develop.
Abstracts of papers presented at the 2nd Meeting of the EPPO ad hoc Panel and 4th International IWGO Workshop on Diabrotica virgifera virgifera LeConte, Gödöllo¨(HU), 1997-10-28/30