Non-Native Insects in Urban and Forest Areas of Slovenia and the Introduction of Torymus sinensis with Dryocosmus kuriphilus

We survey non-native insects species in whole territory of Slovenia. Data on non-native species were collected in field, and we also used results of projects in which we participated and with overview of literature data in scientific pub-lications. Correspondence Analysis (CA) of data was carried out with the soft-ware Statgraphics Centaurion XVI, U.S.A. Up to 254 non-native insect species are present: around 83% are phytophagous (43% feed on woody plants, 40% on other plants);around 12% are non-phytophagous;and 5% are parasitoids or predators of other insects or mammals. Among the phytophagous species, Hemiptera predominates (with 38.2%), followed by Coleoptera (29.8%) and Lepidoptera (14.5%). Non-native insects that do not feed on plants include Coleoptera (80%), Lepidoptera (6.5%), Hymenoptera (6.5%) and Diptera (6.5%). Most of phytophagous species are associated with introduction of plants on which they are specialists, but some have also shifted from introduced to native plant hosts. 36 non-native phytophagous species (14.17% of all non-native insects) have become harmful plant pests of urban trees and crops. 20 appear on woody plants, but only Dryocosmus kuriphilus, appears in urban forest areas. In the past decades species such as D. kuriphilus, Leptoglossus occidentalis, Xylosandrus germanus, Gnathotrichus materiarius, Dasineura gledichiae, Phyllonorycter issikii, Cinara curvipes, Ophiomyia kwansonis have been recorded in parks and forests. Some non-native species are spreading in Slovenian urban forests and affect economic, ecological and other forest and urban forest functions. The number of harmful insects in forests is extremely small probably due to high diversity of the forest ecosystem, where close-to-nature forest management is practiced, which retains forest’s self-regulatory ability to control pests. Such management enables for example the reduction of D. kuriphilus with expansion of its parasitoid, Torymus sinensis. We attempt to explain this phenomenon: we assume that T. sinensis was introduced in Slovenia as diapaused eggs in its host, D. kuriphilus.

Diversity and surge in abundance of native parasitoid communities prior to the onset of Torymus sinensis on the Asian chestnut gall wasp(Dryocosmus kuriphilus) in Slovenia,Croatia and Hungary

Since the rapid spread of the Asian chestnut gall wasp(ACGW) throughout south-east Europe in the last few years,the possibilities of its control have been increasingly investigated.Due to constraints in available suppression measures in forest stands,biological control is recognized as the most suitable action to lower the abundance of the new invasive pest.Torymus sinensis,as a specialized parasitoid chalcid wasp of ACGW,was introduced to suppress the pest in Italy in 2005,and later in Croatia,Hungary(2014) and Slovenia(2015).We investigated the native parasitoid complex associated with ACGW in Slovenia,Croatia and Hungary over 8 years of sampling.We found 41 species of native parasitoids,eight of which are the first records on ACGW in Europe,adding up to a total of 51 species known to parasitize ACGW.These findings represent a large complex of cynipid-parasitoid fauna.Moreover,the abundance of native parasitoid populations on ACGW have demonstrated a temporal surge between the invasion of a new alien host(ACGW) and the onset of its specialized parasitoid,T.sinensis.Our results indicate that the introduced parasitoid acts as a very successful biocontrol of ACGW,outcompeting native parasitoids.This outcome should be considered as beneficial through the maintenance of ecological balance in affected forest ecosystems.