Diabrotica virgifera virgifera in eastern Slovenia: increasing population trend 2005.

The first invasion of the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) into Slovenia was recorded in 2003. A few beetles were found in the western province of Slovenia near Italy. More beetles were detected in the eastern district of Prekmurje bordering Austria, Hungary and Croatia. While the western population remained the same in 2005, the eastern population increased considerably. By means of the very sensitive Metcalf sticky trap baited with the female sex pheromone, early infestations could be recorded. At corn fields, Zea mays L., near the villages of Dolina, Gornji Lakos and Pince, Diabrotica flights were observed in 2005 which had their maxima during the first week of August and yielded, respectively, 57, 112, and 45 beetles/trap per 3-4 day trapping interval. The increase from 2004 to 2005 in this eastern most district of Slovenia is noteworthy. Generally in the western and central part of Slovenia, most maize is grown in rotation, typically every second year. It is estimated that about 10 % of the surface of maize is grown as monoculture, typically on farms with intensive cattle production. In eastern Slovenia, a higher proportion of maize is grown in monoculture (about 30 % in the 3-year period from 2002-2004); this percentage decreased in 2005 due to official requirements by the Slovenian Phytosanitarian Administration.