Review article
ALIEN PHYTOPHAGOUS INSECT AND MITE SPECIES ON WOODY PLANTS IN CROATIA
Dinka Matošević
orcid.org/0000-0001-7380-688X
; Zavod za zaštitu šuma i lovno gospodarenje, Hrvatski šumarski institut, Jastrebarsko
Ivana Pajač Živković
orcid.org/0000-0002-0775-7327
; Zavod za poljoprivrednu zoologiju, Agronomski fakultet, Sveučilište u Zagrebu
Abstract
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
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 the lack of a comprehensive and regularly updated inventory of alien species they have not been listed before. This also makes this up-to-date list of alien phytophagous insects in Croatia valuable. Our results have shown that Asia is the main region of origin of alien insects established in Croatia (33 %), followed by North America (27 %). The trends are similar in other European countries and Europe in general. A rapid increase in the number of new alien species introduction per year in Croatia is noticeable from the years 2007–2012 (6.4 species/year) compared to 2002–2007 (1.8 species/year) (Figure 3). 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 2000–2007 (6.3 species) compared to 1960–1979 (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 (Figure 4). 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 then timber and that ornamental plants constitute "miniature" ecosystems which may host a large variety of insects that have the potential to damage other woody plants as well. Almost 90 % of alien invertebrates in Europe were introduced unintentionally through human activities, mostly as contaminants of a commodity. In Europe, ornamental plant trade contributes significantly more than forestry products to the invasion of alien forest insects. As interception data have not been analysed in this paper, a research of such data for alien insect species and trade volumes in horticultural plants in Croatia is strongly needed. There is a strong suspicion that ornamental plants are one of main pathways of introduction of alien insects to Croatia due to the increase of the imported volumes from year to year. Alien insect species are known for being serious pests worldwide and they can impact habitats which they invade in several ways. Alien insects can affect native biodiversity through direct actions: phytophagous insects feeding on plants, a predator or a parasitoid attacking host, an alien species hybridizing with a native species or indirect actions: vectoring diseases, competing for food, or sharing natural enemies with native species. This research has shown that dangerous pests that can cause direct economic costs have invaded and are spreading in Croatia (Table 1). Due to high percentage of alien insect on agricultural lands (outdoor and in glasshouses) in Croatia (Figure 4) the yield losses of alien insect species on agricultural crops in Croatia must be considerable. Alien insects can have serious negative impact on forests, woodlands and urban parks. Some potentially damaging forest and urban pests have already established themselves in Croatia. In countries where the percentage of forest cover is high (Croatia around 44 %) the damage from alien insects is expected to be considerable. Most introductions of alien insects are unintentional and unpredictable. Less than 20 % of the alien invertebrates in Europe have been intercepted before their arrival. There are several harmful phytophagous alien species 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 colonisation 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 on the Mediterranean coast. One of the main factors, globalisation, will definitely influence the upward trend of introduction and spread of new alien species in Croatia which will negatively influence economy and ecosystems.
Keywords
invasive species; alien species inventory; taxonomy; geographic origin; establishment rate; habitat; damage
Hrčak ID:
101870
URI
Publication date:
30.4.2013.
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