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ŠUMARSKI LIST 3-4/2013 str. 78     <-- 78 -->        PDF

Alien species are defined as species living outside of their natural range and outside of their natural dispersal potential. When an alien species enters a novel environment and has negative ecological and economical impact it becomes invasive species. Alien species are considered as one of the major threats to biodiversity after habitat destruction and enormous damage is done by them to ecosystems and economies. They have been described as an outstanding global problem. Economic damages associated with alien species in several countries in the world amount to about 5 % of the world GNP. Numerous alien insect species, many introduced only in the last 200 years, have become successfully established in various ecosystems in Europe, 1541 species of alien invertebrates are already present, 94 % of them are arthropods and 90 % of them are insects. More than half of the alien invertebrates are phytophagous (52 %) and 30 % of them infest trees and shrubs. Basic knowledge of the identity, origin, pathway, time of introduction of alien species is essential for assessing the threats from alien species and the first requirement when assessing the impact of alien species on ecosystems is to make an alien species inventory of a certain territory or country. Such studies are needed to assess which taxonomic or bio-ecological groups of alien insects are more successful invaders or more harmful to environment and economy. Croatia lacks such an inventory. Even though Croatia was included in most recent and comprehensive study of alien terrestrial arthropodes in Europe, Croatian references with first records were totally missing. There is no up-to-date list of phytophagous alien insect species on woody plants in Croatia. The aim of this paper is to provide up-to-date comprehensive list of known phytophagous alien insect and mite species on woody plants in Croatia with all relevant Croatian references.
The starting point for compiling the list of alien species of phytophagous insects on woody plants in Croatia was a book "Alien Terrestrial Arthropodes of Europe" and database DAISIE. These are primary online resources on alien insect species available to the public and first qualified reference system on invasive alien species for the European region. We compiled the list by searching many sources of forestry, agricultural and taxonomic entomological peer-reviewed literature in Croatia, checklists and primary research publications on alien insect species. The references in these sources were examined for additional relevant publications.
A total of 101 phytophagous alien species (98 insect species from 6 orders and 3 mite species form subclass Acarina) on woody plants were recorded (Table 1) and they are already present in Croatian entomofauna. They were dominated by Hemiptera (56.4 %), Lepidoptera (14.9 %), Hymenoptera (12.9 %), followed by Diptera (5.9 %) and Coleoptera (5.9 %), Acarina (3 %) and Thysanoptera (1 %)(Figure 1). One third (33.7 %) of the alien species in Croatia originate from Asia, 26.7 % from North America while 12.9 % are of tropical origin (Figure 2). From the 101 established alien insect species in Croatia, an increase in the number of introductions can be noted in the first decade of 21st century (Figure 3). Agricultural lands are the most frequently invaded habitats by alien phytophagous insects in Croatia (56.4 %), followed by parks and gardens (28.7 %) and woodlands and forests (14.9 %)(Figure 4).
Order Hemiptera clearly dominates as it includes some of the most successful invaders (57 %) on woody plants in Croatia. Similar results were obtained at a country level for Hungary, Great Britain, Italy, Slovenia and Europe in general. This outcome can be attributed to the fact that species of this order remain undetected and are easily transported due to their tiny size in concert with the intensive trade in agricultural commodities. The occurrence of other orders (Lepidoptera 14 %, Hymenoptera 13 %, Diptera 6 %, Coleoptera 6 %, and Thysanoptera 1 %) is slightly different from other European countries. Results from several investigations have shown strong positive correlations between the number of alien insects per European country and the volume of manufactured and agricultural imports, road network size, the GDP and the geographic size. In contrast, alien species richness was not correlated with the total or percentage of forest cover. The number of alien insects is positively correlated with country surface area, and bordering the sea does not influence the number of alien insect species which is quite important for Croatia. There is a strong correlation between the number of alien insect species and the total amount of imports and level of international trade of the country. It can be predicted that the number of established alien insect species will grow as Croatia shows constant increase of traded commodities with other European and non-European countries. In this review we have listed alien insect species that have not yet been recorded for Croatia on European level. These are Oxycarenus lavaterae; Massilieurodes chitendeni; Adelges (Dreyfusia) nordmannianae; Pineus (Eopineus) strobi; Protopulvinaria pyriformis; Dryocosmus kuriphilus; Platygaster robinae; Aproceros leucopoda; Rhyzobius lophanthae; Rodolia cardinalis; Harmonia axyridis; Xylosandrus germanus; Caloptilia roscipennella; Caloptilia azaleella; Phyllocnistis citrella; Argyresthia thuiella; Cydalima perspectalis; Dasineura gleditchiae; Ceratitis capitata; Rhagoletis cingulata