Jasminka Igrc Barcic, Renata Dobrincic, Milan Maceljski
Agricultural faculty HR 10000 Zagreb, Svetosimunska 25, Croatia;

Monitoring the Western Corn Rootworm (Diabrotica virgifera virgifera LeConte) started in Croatia in 1995 and was continued the following years.

In 1995 cucurbitacin traps, and in all following years Hungarian pheromone traps and various yellow sticky traps were used. The traps were placed in average on 130 - 150 sites.

In 1999 the traps were placed on 117 sites. On each site one pheromone and one yellow sticky trap were placed at least 100 m apart. They were replaced by fresh ones each 25 days, thus 4 pheromone and 4 yellow sticky traps were used on each site. 70% of sites were situated in previously infested areas and 30% in areas which were not infested in June 1999.

The spread of the WCR in the direction to west was in average 20- 50 km per year. The spread was faster along both great rivers which are flowing from west to east: the river Dravaalong the Hungarian border and the river Sava along the border of Bosnia and Herzegovina. The mountain region (600-800 m) between these rivers was overrun by the WCR with some delay. It is interesting to point out that in some sites infested for the first time this year the number of beetles reached: even 25 beetles.

In spite of a very strong traffic from east to west no spread of the WCR by vehicles was registered.

The most farest point of the WCR spread toward west along the river Sava is about 120 km from Slovenia and along the river Drava only 100 km from Austria.

The population density of the WCR was in 1999 much higher than in the previous year.

Altogether, before disposing with all results, we evaluate that the increase factor in the earlier infested areas for 1999 is at least 4 - 5. The increase factor for the years 1997 and 1998 was about 2.8.

In our insecticide trials conducted at a site on the border with Yugoslavia, the highest root damage registered by the Iowa University scale on some plants was 5.5. In this trial on some plants minor goose neck symptoms appeared. The yield losses due to root damages in this trials were 15-20%. No damages caused by the WCR were reported by the corn growers.