Alien phytophagous insect and mite species on woody plants in Croatia.
This review listed alien insect species that have not yet been recorded for Croatia on European level. These are Oxycarenus lavaterae, Massilieurodes chittendeni, Adelges (Dreyfusia) nordmannianae, Pineus (Eopineus) strobi [Cinara 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 and Drosophila suzukii. Some of them are novel and only recently introduced alien species whereas some of them are present for decades in Croatia but due to lack of a comprehensive, regular, and updated inventory of alien species, they have not been listed before. Results have shown that Asia is the main region of origin of alien insects established in Croatia (33%), followed by North America (27%). A rapid increase in the number of new alien species introduction per year in Croatia is noticeable from 2007 to 2012 (6.4 species/year) compared to 2002-07 (1.8 species/year). In Europe, an average of 17.5 new species of insects per year was recorded between 2000 and 2007, while this value was only 8.1 from 1950 to 1974. In Europe, twice as many new insect species were observed per year on trees and shrubs during the period 2000-07 (6.3 species) compared to 1960-79 (3.4 species). The differences between the number of new alien species/year in Europe and Croatia are probably due to differences in sampling efforts, country surface, volume of traded goods etc., but the rapidly increasing trend is obvious. More than 80% of alien insect species in Croatia (57% on agricultural lands and 28% in parks and gardens) have been established in man-made habitats. Only 15% of alien insect species in Croatia have established themselves in natural environments (forests and woodlands), which is almost the same percentage as on European level. It is a common observation that simple, disturbed, man-made habitats are more easily invaded by insects and other invaders than complex, undisturbed, natural habitats. Alien insects linked to human environments and activities (e.g., ornamental plants, bonsais, seeds, large potted trees, cut flowers, vegetables, fruits) are more likely to be carried by human transports into a new region than insects living in natural areas. A study has shown that bonsais carry a more diverse alien insect fauna than timber and that ornamental plants constitute 'miniature' ecosystems which may host a large variety of insects that also have the potential to damage other woody plants. Almost 90% of alien invertebrates in Europe were introduced unintentionally through human activities, mostly as contaminants of a commodity. This research shown that dangerous pests that cause direct economic costs have invaded and are spreading in Croatia. Several harmful phytophagous alien species are approaching the borders of Croatia: Agrilus planipennis, which could pose serious threat to Croatian lowland oak ecosystems, Anoplophora sp. which is spreading rapidly in Northern Italy. Some of the most polyphagous alien insect species, such as Drosophila suzukii, have only recently been discovered in Croatia. This study has also shown a time lag between arrival and first record of an alien species which has direct implications on successful eradication measures. Climate change may directly influence establishment and colonization of alien insect species in new territories- from other continents to Europe and from warmer European regions of Europe further north. Global warming is likely to influence establishment and spread of alien insect species from subtropical and tropical areas (24% found in Croatia) especially in the Mediterranean coast. Further, globalization, definitely influence the upward trend of introduction and spread of new alien species in Croatia.