GIS analysis of the spread and population density ofDiabrotica virgifera virgiferaLeConte and its impact on agricultural practice in Slovenia during the period from 2003 to 2007

Abstract

The western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is one of the most important maize pests, and was introduced to Slovenia in 2003 by natural spread from both the East and West. In Slovenia, as in other European countries, different patterns of spread and population growth of the WCR have been observed in maize growing areas, depending on the density of maize fields in the area and the frequency of maize in the crop rotation. In this study, the spread, population growth and impact on agriculture practice of the WCR have been analysed using GIS tools. In the period from 2003 to 2007, the spread and population growth were observed to be different between western and eastern Slovenia due to differences in population pressure from neighbouring areas and the portion of maize in the area. In the West, the distribution and prevalence of WCR has remained approximately unchanged since the first year of introduction, while in the East, both spread and population growth have become more progressive. However, both parameters showed only moderate progress up to 2006, while in 2007, conditions became more favourable for WCR development and spread. Spread was influenced significantly, although there were only 45 captured imagos per positive PAL pheromone trap per year after 4 years of presence, on average. Moderate growth of the WCR population was a consequence of the implementation of area-wide containment measures in a delimited area, which resulted in a considerable decrease of monoculture maize growth. This altered pattern of agricultural practice was confirmed with GIS analysis in areas that were demarcated in 2004 and 2005. In the maize growing area in the East, the portion of area under monocultural maize cultivation decreased from 28% to 5% in demarcated areas of WCR from 2004 and 2005, and decreased from 18% to 2% in 2007. In the area demarcated in 2004 in the West, the portion of monocultural maize is decreased in 2007 to only 3%, compared with 34% in 2003. Obviously Slovenian farmers have followed the legislation to a great extent and adopted crop rotation as the main WCR control measure. Implementation of area-wide containment measures from the first year of WCR infestation resulted in slower population growth and expansion.