Dispersal and larval hosts of the zigzag sawfly Aproceros leucopoda (Hymenoptera) in Slovakia, Central Europe

Background and purpose The zigzag elm sawfly, Aproceros leucopoda (Hymenoptera), originating from Asia is being considered as one of the major pests of elm trees ( Ulmus spp.) within Europe where it was first recorded in 2003. Recent investigations document the fast spread of this invasive species in many European countries. In Slovakia, A. leucopoda was first recorded in 2009 but its occurrence here has not been reported since 2009. Herein, we summarize the data from the two consecutive years about the current distribution of A. leucopoda and its hosts in Slovakia, Central Europe, focusing on infestation of elm trees by this successful invader in different altitudes. Material and methods In 2014 and 2015 the investigations of A. leucopoda were conducted at 101 different plots across the country. At each plot, characteristic symptoms of leaf damage, occurrence of larvae, cocoons or adults were recorded along with the geographical coordinates and the altitude, and the host trees of A. leucopoda were identified at the species level. The distribution map of A. leucopoda was drawn using the field data. The infestation of elm trees along the altitudinal gradient was analyzed with Kruskal-Wallis non-parametric analysis of variance followed by post-hoc Dunn's test for multiple comparisons. Results and conclusions The zigzag elm sawfly A. leucopoda was observed at 31 plots (30.7%, n = 101). In elm trees examined, generally, a low level of infestation by this pest was observed. A. leucopoda was found at plots between 107 and 701 m a.s.l. The result show that the infestation level of elm trees was decreasing with increasing altitude. Although we had only a small sample of data, we assume that the altitude has a significant effect on distribution of this pest. The field elm ( Ulmus minor Mill.) was the most frequently utilized host. Data collected document the establishment of this successful invader in Slovakia.