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ŠUMARSKI LIST 7-8/2013 str. 30     <-- 30 -->        PDF

pests (Grapputo et al. 2005; Rubinoff et al. 2010; Bray et al. 2011). Europe has suffered several invasions of exotic insect species, some of which have become serious pests that cause considerable damage (Matson et al. 2007; DAISIE 2009; Kenis et al. 2009, Blank et al. 2010).
One of the latest insects that invaded Europe is Dryocosmus kuriphilus Yasumatsu (Hymenoptera; Cynipidae), which is a global pest of chestnut (Castanea). The chestnut gall wasp is a univoltine species, that reproduces parthenogenetically laying eggs in the buds of Castanea spp. during summer. A direct consequence of this modus vivendi is that even a single female is capable of establishing a population (Nohara 1956; Askew 1984). In addition to that, eggs and first instars that grow in chestnut buds, render this species practically undetected (Panzavolta et al. 2011). By attacking vegetative buds D. kuriphilus disrupts twig growth and reduces fruiting that can ultimately lead to losses of up to 70 % (Dixon et al. 1986; EPPO 2005). Being under this stress, chestnut trees exhibit a gradual decline in biomass coupled with a decline in the aesthetic and the amenity value (EFSA 2010).
Even though it is native to China, D. kuriphilus was first recorded in Japan in 1941 (Murakami 1980). This was the first invasion of the chestnut gall wasp, that occurred rapidly (in 25 years) (Oho & Umeya 1975) and had serious impact on chestnut production. In the years that followed, D. kuriphilus expanded into Korea and South Korea in 37 years (Aebi et al. 2006). Not late afterwards, it was introduced in America (Payne et al. 1975), putting at risk the American chestnut production (Cooper & Rieske 2007). In Europe, chestnut gall wasp was first reported from Piedmont in noth-west Italy in 2002 (Brussino et al. 2002), introduced with chestnut cultivars from China (Quacchia et al. 2008). Since then, D. kuriphilus expanded rapidly taking actually Europe by storm. By 2005 it has spread in Sicily, south eastern France and Corsica (Aebi et al. 2006) as well as in Slovenia (Knapič et al. 2010). A year later it was found in Hungary (Csóka et al., 2009) and Switzerland (Forster et al. 2009), arriving in Netherlands and Croatia (Matošević et al. 2010) in 2010.
As genetic polymorphisms accumulate over time, they enclose valuable information regarding the invasion history of a species, a reason that explains the wide application of molecular techniques in studies of invasive species (Fitzpatrick et al. 2012). Among different markers available, mitochondrial DNA markers are broadly selected in such investigations (Cognato et al. 2005; Bray et al. 2011), as they are expected to evolve rapidly, something that adds to their sensitivity (Avise 1994). Here, we employ a mtDNA marker, to study the genetic variability of D. kuriphilus for the first time after its introduction in Europe. Comparing our data, with previous results from China reveals not only the origin of the source population, but also the expanding potential of this pest species. Though preliminary, our research offers a first insight into the on-going invasion of Europe by D. kuriphilus, providing information that can be used to plan and improve management strategies.
Materials and Methods
Materijali i metode
Following the expanding distribution of D: kuriphilus in Europe, 96 specimens belonging to 9 different locations were sampled in two successive years (namely 2011 and