Appearance and migration of the horse-chestnut leafminer Cameraria ohridella in relation to city size and leaf-raking, using the example of two cities in Western Poland

Abstract

Possible differences in the size and dynamics of the appearance of particular generations of Cameraria ohridella were studied at two city sites of different size and character. The differences in the degree of infestation of Aesculus hippocastanum by the horse chestnut leafminer in the two towns are interpreted as a result of the differences in the size of food resources. The greater degree of infestation of trees in Mosina relative to trees in Poznan´is most probably a result of the difficulty of aerial dispersion and thereby much stronger competition for food. This conclusion confirms a positive correlation of the distance between localities with the degree of tree infestation in a small town and the lack of such a correlation in a big city. The presence of refuges in the city outskirts at which no raking and removal of leaves is performed does not seem to have a significant effect on the degree of horse chestnut infestation in the centre.

Spatial variability in the level of infestation of the leaves of horse chestnut by the horse chestnut leaf miner, Cameraria ohridella (Lepidoptera: Gracillariidae) and in the number of adult moths and parasitoids emerging from leaf litter in an urban environment

“…density of C. ohridella at a site is not associated with the density at neighbouring sites. Similar fi ndings are reported by Baraniak et al (2004Baraniak et al ( , 2005 who found a positive correlation of the distance between localities with the degree of infestation of trees only in a small town and only during the third generation of C. ohridella larvae. These authors conclude that the presence of refuges in the city outskirts, where there was no raking and removal of leaves, did not seem to have a signifi cant effect on the degree of horse chestnut tree infestation in the centre.…”

“…This indicates a persistent and long-standing problem at individual sites. This fi nding is supported by many other studies (Kehrli & Bacher, 2003;Baraniak et al, 2004Baraniak et al, , 2005.…”

“…Their results indicate a strong spatial dependence of infestation level up to a distance of about 1 and 2 km in Bern and Brussels, respectively, and quantitatively demonstrate that the amount of leaf litter left at a site is the main factor explaining the variability in the level infestation by C. ohridella. In contrast, studies carried out in Poland indicate that the mean distance between horse chestnut trees has a signifi cant effect on the infestation level only in the third generation of C. ohridella larvae and only in small towns (Baraniak et al, 2004) while in large towns it has no effect (Baraniak et al, 2005). In both studies the correlation between infestation and distance to uncontrolled sites, i.e.…”

“…Gilbert et al (2003) and Baraniak et al (2005) report that the level of infestation by C. ohridella is correlated with the amount of leaves recorded at a site overwinter. Maintenance of green public areas thus has a signifi cant effect on the horse chestnut leaf miner and the only effective way to regulate the damage caused by C. ohridella in spring is raking and removing leaf litter in autumn or early spring (Kehrli & Bacher, 2003).…”

“…However, this prediction does not take into consideration outbreaks of horse chestnut leaf miner occurring close by (Baraniak et al, 2005). Spatial analysis based on Moran's index describes the degree of spatial autocorrelation among sites (Chen, 2013).…”