Weevils and Bark Beetles (Coleoptera, Curculionoidea) Chapter 8.2

We record 201 alien curculionoids established in Europe, of which 72 originate from outside Europe. Aliens to Europe belong to fi ve families, but four-fi fths of them are from the Curculionidae. Many families and subfamilies, including some species-rich ones, have few representatives among alien curculionoids, whereas some others are over-represented; these latter, Dryophthoridae, Cossoninae and specially Scolytinae, all contain many xylophagous species. Th e number of new records of alien species increases continuously, with an acceleration during the last decades. Aliens to Europe originate from all parts of the world, but mainly Asia; few alien curculionoids originate from Africa. Italy and France host the largest number of alien to Europe. Th e number of aliens per country decreases eastwards, but is mainly correlated with importations frequency and, secondarily, with climate. All alien curculionoids have been introduced accidentally via international shipping. Wood and seed borers are specially liable to human-mediated dispersal due to their protected habitat. Alien curculionoids mainly attack stems, and half of them are xylophagous. Th e majority of alien curculionoids live in human-modifi ed habitats, but many species live in forests and other natural or semi-natural habitats. Several species are pests, among which grain feeders as Sitophilus spp. are the most damaging.


Introduction
Th e superfamily Curculionoidea encompasses the weevils and the bark and ambrosia beetles; here we will use "weevils" to refer to the entire superfamily. It is the most species-rich beetle clade, with more than 60,000 described species (Oberprieler et al. 2007). Four fi fths of all weevils are in the family Curculionidae. Curculionoids are distributed worldwide, everywhere vegetation is found. Th is is a rather homogeneous group, its members being generally easily recognizable despite various aspects. Adults are primarily characterized by the head being produced into a rostrum (snout) to which the antennae and mouthparts are attached. Th e rostrum is highly variable in size and shape, varying from as long as the body to very short or absent. Larvae, generally white and C-shaped, are catepillar-like (eruciform), soft-bodied, with legs being either vestigial or (usually) absent, except in some species of the primitive family Nemonychidae.
Except for a few rare species, adults and larvae of Curculionoidea are phytophagous. Larvae are mainly endophytic or subterranean. Weevils feed on a large variety of plants, attacking all parts. Many species are important pests for agriculture or forestry.
Th e Macaronesian islands 1 pose a special problem. While many of their weevils are only found on single islands or groups of islands and are thus clearly endemic, other species are shared between island groups, or between Macaronesian islands and the continental Europe or North Africa. For example, a number of scolytines specialized to Euphorbia are shared between the Canary Islands and Madeira, or between the Canary Islands and the Mediterranean and North Africa (Table 8.2.1). Given the diffi culties involved with dispersal by these tiny insects over vast expanses of salt water, we have chosen to interpret the distributions of non-endemic species as resulting from recent human transport. We are well aware that rare instances of natural dispersal do occur, at least on evolutionary time scales: after all, such natural dispersal has resulted in many instances of well documented species radiations (Emerson 2008, Juan et al. 2000. Because of the inherent uncertainty in distinguishing between recent anthropogenic spread and older natural dispersal, we classify nonendemic species of these archipelagos as presumed aliens (they are indicated in tables 8.2.1 & 8.2.2). Without contradictory data, we consider: 1) species known from Europe and found on a Macaronesian island as presumed alien in Europe; 2) species known from Africa (and not from Europe) and found in Macaronesia as presumed alien to Europe; 3) species from the Canary Islands which also occur further north on Madeira or the Azores as presumed alien 1 We include in our coverage the Macaronesian islands associated with European countries (Madeira, the Azores, the Canary Islands); we exclude the Cape Verde Islands. from the Canary Islands and presumed alien to Europe. Presumed alien are often considered below separately than others, due to the uncertainty attached to their status and the geographical and biogeographical diff erences between Macaronesia and Europe.
We consider that 201 alien curculionoids currently live in Europe, of which 72 species originate outside of Europe (aliens to Europe, Table 8.2.1; 20 presumed alien are included) and 129 species originate from other parts of Europe (aliens in Europe, Table 8.2.2; 60 presumed alien are included) 2 . Except where otherwise noted, our discussion of exotic curculionoids only pertains to alien to Europe.

Taxonomy and biology
Th e systematics of the superfamily Curculionoidea have long been controversial, in part due to the enormous number of taxa involved, in part due to extensive parallel evolution arising from the similar ecologies of unrelated clades (Alonso-Zarazaga andLyal 1999, Oberprieler et al. 2007). We follow here the current classifi cation of Fauna Europaea (Alonso-Zarazaga 2004), which notably considers the traditional Platypodidae and Scolytidae families as subfamilies of Curculionidae.
About 5,000 native curculionoids live in Europe, distributed among 13 families. Comparatively, the alien entomofauna is very limited with only 72 established spe cies recorded at this time ( Fig. 8.2.1). Th ese alien species belongs to fi ve families, all of which have native representatives.
Anthribidae. Principally present in tropical areas, these largely fungus-feeding curculionoids generally live primarily in fungus-infested wood. Th ere is only one alien species in Europe, Araecerus coff eae, which is a seed feeder, an exceptional biology in this family.
Apionidae. Characterized in part by their non-geniculate antennae and endophytous larvae, these tiny curculionoids are represented in Europe by three alien species, all living on alien ornamental Alcea (Malvaceae).
Dryophthoridae. Th is family contains large weevils mainly living on woody monocotyledons. Alien dryophthorids consist of woody monocotyledons borers and seed feeders. Th ey are particularly numerous compared with the world fauna ( Fig. 8.2.1) and especially with respect to the few native species in Europe (8 aliens vs 6 natives, according to Fauna Europaea (Alonso-Zarazaga 2004)). Th is situation could be explained fi rst by the few woody monocotyledons in Europe-native fl ora in contrast with the several woody monocotyledons introduced in Europe for ornamental or agricultural purpose. Th e human-mediated transport of seeds, and consequently seed feeders, is probably a further explanation. 2 Other aliens have been recorded, but have not been taken into account here because their establishment have not been confi rmed. We have also excluded some possible presumed aliens due to the uncertainty about their distribution.

Erirhinidae.
Curculionoids of this small family mainly live on herbaceous monocotyledons, often aquatic ones. With two alien species, they are relatively well represented in Europe.
Curculionidae. Th is huge family encompasses more than 80% of weevils and notably includes the bark beetles and pinhole borers (Scolytinae and Platypodinae). Curculionids have a large variety of habits, but are all phytophagous. Th e European species are distributed in 16 subfamilies. Th e alien species belong to 10 subfamilies, all having native representatives. Many subfamilies, including the world's largest (Entiminae, Curculioninae and Molytinae), are under-represented among alien curculionoids compared with their world importance in the superfamily (Fig. 8.2.1). On the other hand, the subfamily Cossoninae, which mainly contains wood-boring weevils, are over-represented, but the most remarkable result is the over-representation of Scolytinae. Scolytinae are small, cylindrical wood borers, without a rostrum or with only a very reduced one; they include some of the most important forest pests in the world. Th e majority are phloeophagous, breeding in the inner bark. Most others are xylomycetophagous, feeding on symbiotic fungi which they cultivate in tunnels in the wood (ambrosia beetles). Th e scolytines represent about 10% of world curculionoids but almost half of curculionoids alien to Europe. Alien bark beetles represent more than 12% of all bark beetle species in Europe. Th e over-representation of Scolytinae is related to the frequency with which they are transported in wooden packing material, pallets, and timber (Haack 2001, Brockerhoff et al. 2006. All stages of these beetles can survive long voyages well, since both adults and larvae are in tunnels under bark or in wood and not directly exposed to temperature extremes or dessication. Th e importance of a stable, protected microenvironment is illustrated by the high prevalence of ambrosia beetles in the Scolytinae plus Platypodinae (35%) among successful aliens to Europe (Table 8.2.1), compared with the prevalence of ambrosia beetles in these groups in temperate climates generally (below 20%: Kirkendall 1993). Th e establishment of ambrosia beetles in Europe is further facilitated by polyphagy (11/12 spp.) and inbreeding (10/12 spp.), as is generally believed to be the case for ambrosia beetles globally (Kirkendall 1993, Haack 2001. Th e curculionoids alien in Europe are more representatives of Europe-native fauna. Scolytines (25% of aliens in Europe) are also over-represented compared with their importance among European curculionoids (5%), but not cossonines (3% of aliens in Europe). On the other hand, Entiminae (26% of alien in Europe, mostly Otiorhynchus and Sitona) are under-represented compared with the European fauna, but less so than among aliens to Europe.

Temporal trends
Of the fi ve families considered in this chapter, the fi rst information concerning an alien species in Europe was probably the description by Ratzeburg in 1837 of Xyleborus pfeilii based on specimens from southern Germany 8 . Th e curculionid Pentarthrum huttoni was introduced to Great Britain from New Zealand in 1854, and has subsequently become naturalized in many European countries (Table 8.2.1). Only three other introduced species were recorded in the second half of 19 th century.
With the beginning of the 20 th century, alien species began to be discovered more frequently, though this was limited to sporadic introductions (about 2 species per decade) confi ned to southern Europe -which perhaps provided more favourable climatic conditions -and along the main routes of international trade. Since the 1920s the rate of new introductions has slightly increased ( Fig. 8.2.2), with a mean of nearly three species every decade, but remaining stable until middle of 1970s.
Despite the European laws regulating the trade of plant material, the number of records of new exotic species introduced to Europe has increased rapidly since 1975 and especially since 2000, reaching worrying levels with an average of more than one species per year (16 new species from 2000 to 2009: Table 8.2.1), and a peak of fi ve new species per year in 2004 (8 species in 2003-2004). It is too early to say if the relatively low number of establishments observed since 2005 will be confi rmed or is only due to stochastic variations. However, if the trend towards increasing rates of introduction continues unabated, in a few decades the mean number of alien species becoming established in Europe could reach several per year.
Th e temporal trend of alien curculionoids establishment is very similar to that observed in Europe for all alien terrestrial invertebrates , but see also Smith et al. 2007 for contradictory (more limited) data). On the other hand, this trend varies among weevils. Aliens from Asia follow the general trend (half of them have been recorded after 1975, a third after 2000), but the increasing of establishment rate is faster for those from North and South America (two-thirds of them have been recorded after 2000) while it is slower for those from others continents (half of them have been recorded before 1950, and none after 2000). Regarding feeding habits, all aliens follow the general trend except those with spermatophagous larvae, which show no trend. Th is particularity of the formers seems related to the oldness and intensity of human-mediated seed transport.
Unfortunately, for many alien species spread over large parts of Europe, data on the place and time of introduction are lacking, and generally the data on time of arrival of exotic species are very weak. Often, introduced species -especially those which are not pests -are fi rst noticed only many years after arrival, or following subsequent and repeated introductions. As prompt communication of new fi ndings is extremely important for the application of specifi c monitoring and eradication programs, the poor quality of these data is a major obstacle to aliens management.  Table 8.2.1.

Origin of alien species
All presumed aliens probably come from Africa (among which 35% from the subregion Macaronesia). Th ese species are not included in further discussion due to uncertainty of their status and specially because their arrival modes have probably been diff erent from other aliens due to proximity of the source region.
A probable region of origin could be specifi ed for 51 of the 52 curculionoid species alien to Europe. Th ere is one species, Sitophilus zeamais (Dryophthoridae), whose region of origin is uncertain (cryptogenic). Cryptogenic species are thus rare in this group compared to all alien terrestrial invertebrates (14%: Roques et al. 2009). Sitophilus zeamais is associated with maize crops, Zea mays, and feeds on maize grain stores, and it is likely that this species is American.
More than one-third (40%) of the exotic curculionoid species originate from Asia. Central and South America represents the second most important region of origin, with 19% of the species coming from this area. North America and Australasia both represent 14% of the contributing regions. Africa is a minor region of origin (6%), and the remaining species (6%) arrived from tropical or subtropical areas but the region of origin could not be precisely identifi ed (Figure 8.2.3). Th is distribution is rather similar to that for all alien terrestrial invertebrates ). Th e main diff erences are the under-representation of African aliens (6% vs. 12%) and the overrepresentation of South American (19% vs. 11%) and Australasian (14% vs. 7%) ones. A rather surprising result is that species originated from areas with tropical or subtropical climates all around the world represent about half of alien curculionoids.
Th irteen out of the twenty-one alien species originating from Asia are from the family Curculionidae, twelve species belonging to the subfamily Scolytinae and one species to the subfamily Cyclominae. Other families consist of Dryophthoridae (4 spp.), Apionidae (3 spp.) and Anthribidae (1 sp.). Scolytines originate from very different parts of this large continent. For example Cyclorhipidion bodoanus is native to Siberia and temperate northeast Asia, Phloeosinus rudis to Japan, and the three species of the genus Xylosandrus to Southeast Asia. In contrast, all the weevils of the Dryophthoridae family originate from tropical Asia. Th is group includes the banana root weevil Cosmopolites sordidus, the coconut weevil Diocalandra frumenti, the palm weevil Rhynchophorus ferrugineus and the rice weevil Sitophilus oryzae. Th e introduced apionids, Alocentron curvirostre, Aspidapion validum and Rhopalapion longirostre, all feed on fl owers and seeds of Alcea rosea and other Malvaceae species (Bolu and Legalov 2008); these all originate from central Asia. Finally, the anthribid Araecerus coff eae originates from India.
Th e ten curculionoid species coming from Central and South America consist of curculionids (8 spp.) and dryophthorids (2 spp.). Curculionids originating from this region are as highly diverse taxonomically (they are distributed in six subfamilies) as in feeding habits. Th e native ranges of many species largely extend through the continent (including sometimes part of North America), though those of others are more narrow as for Rhyephenes humeralis (central Chile and neighboughring area of Argentina) and Paradiaphorus crenatus (Brazil).
Seven alien curculionoids are known to originate from North America. Th ey include fi ve species of the family Curculionidae and two of Erirhinidae. Many curculionids introduced from North America are xylophagous sensu lato 7 , feeding on several broadleaved or coniferous hosts. Th e exceptions are the ash seed weevil Lignyodes bischoffi and Caulophilus oryzae, originally from the southeastern USA, which feeds on seeds. In contrast, the two Erirhinidae species feed externally on weed roots and ferns, respectively.
Seven curculionoid species come from Australasia, all curculionids: four cossonines, two molytines and one cyclomine. Th ree woodboring weevils ( Pentarthrum huttoni, Euophryum confi ne and E. rufum, all from Cossoninae), feeding on decaying wood, originate from New Zealand. Th e four other species were unintentionally introduced from Australia. All feed inside plant material (xylophagous or herbiphagous), except the Eucalyptus snout beetle, Gonipterus scutellatus, a defoliator of Eucalyptus trees originated from Southern Australia.
Only three curculionoid species are known to originate from Africa, a curculionine and two scolytines. Th e palm fl ower weevil, Neoderelomus piriformis, probably originates from North Africa; it feeds on but also pollinates fl owers of palms like Phoenix canariensis. Th e scolytines both originate from Canary Islands; Dactylotrypes longicollis breeds in Phoenix canariensis seeds, while Liparthrum mandibulare is a highly polyphagous phloeophage.
Th ree cosmopolitan curculionoid species originate from undetermined areas of the tropical and subtropical parts of the world: the tamarind seed borer, Sitophilus linearis (Dryophthoridae), and the palm seed borers Coccotrypes carpophagus and C. dactyliperda (Scolytinae). As seed-feeders, they are readily distributed through commerce, which probably explain the uncertainty about their origin. Concerning the curculionoids alien in Europe, nine-tens of these (114 spp. among 129, Table 8.2.2) are introduced from mainland Europe to islands (mainly the Canary Islands, the Azores, the British Isles and Madeira). Th ey are often widespread continental species which have been introduced to islands by human transport. Other cases are mainly species of southern and western regions which were introduced into northern Europe (as Otiorhynchus corruptor), especially to Denmark and Sweden. However, some species have moved westwards (as Otiorhynchus pinastri and Phloeotribus caucasicus) and even southwards ( Ips duplicatus).

Distribution of alien species in Europe
As for the other arthropod groups, alien curculionoid species are unevenly distributed throughout Europe, which may partly refl ect diff erences in sampling intensity (Fig. 8.2.4,Table 8.2.1). In continental Europe, mainland Italy and France host the largest number of species alien to Europe, with 28 and 26 introduced curculionoid species, respectively. Th ese countries are followed by continental Spain (17 spp.), Austria (15 spp.), and Germany, Switzerland and United Kingdom 3 (13 spp.). Th is distribution is similar as that of all alien terrestrial invertebrates ). Th e number of aliens per country signifi cantly decreases eastwards (y=12 -0.29*longitude, R 2 =0.21, F 1,31 =8.08, p=0.008), but it is mainly correlated with human variables, country population (y=-1.5 + 3.7ln(population), population in million inhabitants, R 2 =0.39, F 1,31 =19.6, p=1*10 -4 ) and country importation values (y=-32 + 3.5ln(value), value 2003-2007 in million USD: Th e World Factbook 2009, R 2 =0.53, F 1,29 =32.4, p=4*10 -6 ) 4 . Th e best model integrates importations and latitude (y=-19 + 3.6ln(value) -0.28*latitude, value in million USD, R 2 =0.60, F 2,28 =20.6, p=3*10 -6 ), indicating that alien establishment is favored by human trade and warm climate. Th e abundance of aliens in mainland Italy and France is not fully explained by the model (predicted values 17 and 16 alien species, respectively); it is likely related to a combination of the diversity of habitats and plants present with the favorable climate and the importance in international shipping.
Islands have a rather rich alien curculionoid fauna, especially Macaronesia: 29 (of which 14 presumed), 18 (8 presumed) and 10 (2 presumed) species in the Canary Islands, Madeira and the Azores, respectively. Th ese islands are followed by Sicily (10 spp.), Corsica (8 spp.) and Malta (6 spp.). As it has been found for other alien terrestrial invertebrates ), the number of alien curculionoids per km 2 in European islands is higher than in continental countries (on average 2.8 vs 0.17 3 Concerning species alien to Europe, United Kingdom characteristics are closer to those of continental countries than to those of other islands, so we consider it as part of continental Europe. Th is is likely related to its large size and population. alien/1000km 2 , R 2 =0.10, F 1,58 =6.56, p=0.013). Aliens density is specially high in Madeira and Malta (23 and 19 alien/1000km 2 , respectively), perhaps because these tiny islands are stopping places on trade routes. Islands show no global trend of alien distribution. However, cold nordic islands (Greenland, Iceland, Svalbard) host few aliens, and in Macaronesia alien number (specially presumed alien number) decreases when distance to continent increases.
Near half of alien curculionoid species (33 spp.) have been observed in only one country, most of them (31 spp.) in a peninsular region or on islands: Italy, Iberia, Macaronesian islands, Malta or the British Isles. Aliens introduced to such areas are less likely to move to nearby countries in comparison with aliens in other mainland regions, but Austria and Russia also host each an own alien species. As examples, Syagrius intrudens from Australia is encountered only in Great Britain, Naupactus leucoloma, from South America, is found only in the Azores, and Paradiaphorus crenatus, from Brazil, is known only from the Canary Islands. After the Canary Islands, Italy hosts the highest number of alien species unique to one country, eight in total, of which six are from subfamilies Scolytinae and Platypodinae. Also, the recent arrival of these species, most of them having fi rst been discovered later than 2000, may in part explain their currently restricted distribution.
Ten alien species (14%) are limited to two countries. In almost all cases, the species are found in neighbour countries, as with the scolytine Dryocoetes himalayensis in France and Switzerland, and Macrorhyncolus littoralis in Great Britain and Ireland. One alien species, Scyphophorus acupunctatus, occurs in two distinct regions, Sicily and France, suggesting the possiblity of multiple introductions (this suggestion is supported by the previous interceptions of this species in diff erent european countries: EPPO 2008).
At the other extreme, the rice weevil Sitophilus oryzae has been found in 34 European countries, and two other seed feeders, Sitophilus zeamais and Rhopalapion longirostre, occur in 23 and 21 countries. Th eir feeding habits in association with frequently transported seeds or stored products presumably explain this broad distribution. Another eleven species are found in 10 or more countries. Th ese include several longestablished species: Xyleborus pfeilii 8 , the wood-borer Pentarthrum huttoni, the palm seed borer Coccotrypes dactyliperda and the parthenogenetic weevil Asynonychus godmani. However, the relatively recently introduced (1993) palm weevil Rhynchophorus ferrugineus is also widely distributed, occurring in most of the Mediterranean region, which attests their high dispersal capabilities (natural and human-mediated). Overall, alien weevil species are more widespread in Europe than other alien terrestrial invertebrates, with 40% of species distributed in more than two countries vs. only 22% ).

Main pathways and factors contributing to successful invasions
Th ere are two components to successful invasion, dispersal and establishment. Dispersal to new continents by phytophagous arthropods is now almost entirely due to human transport, the magnitude of which has inceased exponentially in recent decades. Plant feeding arthropods are carried in and on live plants and fruits, in wood, and as stowaways in shipments and baggage. Deliberate introductions of arthropods are less frequent, and most involve exotic organisms imported for biological control. Establishment of new arrivals depends on availability of appropriate habitats near sites of introduction, ability to compete with similar species already present, and on a reasonable tolerance for the local climate.
All exotic species of Curculionoidea have been introduced accidentally in Europe, vs. only 90% for all alien terrestrial invertebrates . Th e lack of intentional introductions of weevils could be related to their poor potential for biological control. One exotic weevil species (Stenopelmus rufi nasus) has been used successfully for biological control of the American water fern Azolla fi licoides in South Africa and to a less extent in the British Isles, but its fi rst introduction in Europe was accidental (Sheppard et al. 2006, Baars andCaff ery 2008).
As is the case for other regions in the world, many of Europe's alien curculionoids have presumably arrived via the shipping of wooden materials: pallets, crating, and barked or unbarked timber (Brockerhoff et al. 2006, Haack 2001. Bark and wood boring species make up half of all alien weevils (50%); these have almost certainly been introduced with wood transport and solid wood packaging materials. Logs with bark are ideal for transporting bark beetles and other weevils. However, even debarked logs can contain live wood borers such as ambrosia beetles. Although some wood-boring beetles have more restrictive requirements (e.g. high humidity and decayed wood: Euophryum confi ne, E. rufum, Pentarthrum huttoni), even these can often survive a few days or even weeks of transport. Th e east Asian ambrosia beetle X. germanus provides a typical example for entry by wood-borers. It was introduced to the USA (1932), where it was discovered in imported wine stocks in greenhouses; the species spread rapidly and has become an important nursery pest in warmer parts of eastern North America (Ranger et al. 2010). In Europe, it was fi rst recorded after World War II, in Germany, where the species probably had been introduced with wood imported from Japan to southern Germany early in the 20th century; the present distribution area includes twelve European countries (Table 8.2.1).
Seed feeders (20%) are introduced with the seeds, which are also an excellent way for transporting insects. Several of these species are associated with agricultural products (e.g. Caulophilus oryzae, Sitophilus oryzae and S. zeamais), however most species feed on ornamental or forest seeds (e.g. Rhopalapion longirostre on Alcea, Lignyodes bischoffi on ash seeds, Dactylotrypes longicollis on palm seeds).
Other alien species (30%) live on or inside leaves and nonwoody stems, or in the soil. Th e formers can be introduced with their host plants or with host plant products (e.g. Gonipterus scutellatus with eucalyptus, Listroderes costirostris with plants such as tobacco); weevils living around roots (e.g. Asynonychus godmani) are transported with living plants. Th ese feeding habits (plus root boring, which doesn't exist among aliens to Europe) are more frequent among presumed aliens to Europe and among aliens in Europe (52%); both cases result from a rather short distance transport, which likely allows survival of less protected insects (among wood boring scolytines, phloeophagous species are similarly much more frequent than xylomycetophagous species among presumed aliens to Europe and among aliens in Europe, contrary to what is observed among other aliens to Europe).
Currently, most introductions are due to international trade, but the increasing movement of fruits and plants by travelers, which is much more diffi cult to check, may contribute to the future diff usion of new alien species.
Newly arrived phytophages must fi nd suitable hosts. Th e likelihood of success is greatly enhanced if the species is not too host specifi c, or if its preferred hosts are abundant. Not surprisingly, the majority of established exotic weevils in Europe are polyphagous, and the hosts of others are often widespread and abundant plants (Table 8.2.1).
Parthenogenesis and inbreeding further increase the chances for successful colonization. When an exotic species is fi rst introduced to a new area, it faces a varie-ty of problems associated with low density which reduce the likelihood of successful establishment and slow the rate of invasion (Tobin et al. 2007, Liebhold and Tobin 2008, Contarini et al. 2009). New populations create problems for mate fi nding; parthenogenetic females do not mate, and inbreeding females mate with brothers while in the natal nest, before dispersal (Jordal et al. 2001); in both cases, there is no problem of mate location and new populations can be established by single females. Very small populations (such as those in recent colonizations) may suff er from high levels of inbreeding depression (Charlesworth and Charlesworth 1987); however, regular inbreeding species such as the invasive scolytines have presumably purged their genomes of the deleterious alleles responsible for inbreeding depression (Charlesworth and Charlesworth 1987, Jordal et al. 2001, Peer and Taborsky 2005. Only a few invasive curculionoid species are parthenogenetic: Asynonychus godmani, Lissorhoptrus oryzophilus, Listroderes costirostris (Morrone 1993) and Naupactus leucoloma, whose males are unknown outside its native range (Lanteri and Marvaldi 1995). However, over half of the alien scolytines inbreed (59%, presumed aliens excluded), compared with less than a third of scolytines native to Europe and about a fourth of Scolytinae species worldwide (Kirkendall 1993).

Most invaded ecosystems and habitats
All alien curculionoid species are phytophagous, as are nearly all curculionoids worldwide. Most of the species have a cryptic way of life, at least during larval stage, fee ding inside plant tissues such as stems or seeds, or living in the soil; only 9% are leaf/stem browsers. Stems and trunks is the major feeding niche of most alien curculionoids (65%). Most of these are bark beetles, ambrosia beetles or other wood borers (50%); herbiphagous (15%) comprise the remaining. Seeds are the second most important feeding niche (18%), followed by leaves (9%; some species could also attack non woody stems) and roots (6%). Last species, Neoderelomus piriformis, feeds on fl owers, and acts as pollinator in palm trees.
Near half of the alien curculionoid species established in Europe colonize urban and peri-urban habitats, primarily parks and gardens (27%) and around buildings (11%). Woodlands is also a frequent habitat for the alien curculionoids (27%), beyond natural heathlands (16%), cultivated agricultural lands (9%) and greenhouses (5%). Only three species occur in wetland habitats, one in coastal and two in inland surface water ( Fig. 8.2.5). Th e importance of natural heathlands is in fact mainly limited to specifi c areas, most of the species recorded in these habitats being presumed aliens attacking euphorbias in Macaronesian xerophytic heathlands.
Th is pattern diff ers from the average value observed for all arthropods, where only a fourth of the species is recorded in natural or semi-natural habitats, and where agricultural lands and greenhouses contain more alien species than woodlands. Th at could be obviously related to the high frequency of xylophagous sensu lato 7 habits in alien curculionoids. Both deciduous trees, such as Populus sp. and Fraxinus sp, and conifers in the genera Picea and Pinus are colonized by several alien curculionoid species utili zing trees. Eucalyptus plantations are also aff ected by a defoliating curculionid, Gonipterus scutellatus, both host and weevil originating in Australia. In urban and suburban areas such as gardens and parks, other trees species, mainly exotics and in particular palm trees, are also aff ected by alien curculionoids.

Ecological and economic impact
Ecological impacts of alien insects are poorly known in general (Kenis et al. 2009), and the impacts of Curculionoidea species alien to Europe seem not to have been documented at all.
Th eir economic impact is better known, refl ecting the economic importance of many of these alien species. A third of the Curculionoidea species alien to Europe (26 species) have a known economic impact, a much higher proportion than for native weevils, even though the latter contain numerous pests. Nevertheless, this high proportion may partly be an artefact, since pests have a higher probability of being detected.
Th e most damaging species are the four attacking stored products. Th e rice weevil Sitophilus oryzae and the maize weevil S. zeamais are among the main pests of stored grains worldwide, destroying signifi cant amounts and incurring high pest management costs 5 (Balachowsky 1963, Pimentel 1991. Larvae develop in cereal seeds and adults feed on these seeds as well as on a wide variety of stored products, products derived from cereal grains and even dried vegetables. Damages is exascerbated by incompletely dried stored products (Balachowsky 1963). In addition to their direct damage, these species facilitate attacks of grains by other pests. Caulophilus oryzae, a less widespread species, sporadically causes the same kind of damages, while Araecerus coff eae attacks grains but mainly less common products such as stored coff ee and cocoa beans.
Five species attack native or introduced cultivated plants. Listroderes costirostris attacks a wide range of vegetables and weeds; adults can also damage foliage of fruit trees. Th e recently established whitefringed weevil, Naupactus leucoloma, is also highly polyphagous; its soil-inhabiting larvae are a serious pest of many agricultural crops. Th e banana root weevil, Cosmopolites sordidus, and Paradiaphorus crenatus are important pests of tropical cultures (banana and pineapple, respectively). Th eir economic impact is currently limited in Europe due to the limited distribution of their hosts in this area and a rather low aggressiveness in its climate, but it could increase later in the future according to the global warming. Th e last species is the rice water weevil, Lissorhoptrus oryzophilus. Recently introduced in Europe, it is a major pest of rice, but also attacks indigenous Carex.
Eight species damage diff erent ornamental plants and trees, mainly introduced tropical or subtropical species. Th e palm weevil Rhynchophorus ferrugineus is a dangerous pest of palms which has rapidly colonized the Mediterannean basin. On the Canary Islands, palms are also attacked by the lesser coconut weevil Diocalandra frumenti. Even if damage are mainly esthetic, they are worrying because this insect princi-5 Damages are also due to the grain weevil S. granarius, probably alien too, but not taken into account here because it has been established in Europe at least since Antiquity. pally attacks Phoenix canariensis, an endemic palm which is emblematic of the Canary Islands where it is widely used for landscaping and is a major element of coastal landscape. Asynonychus godmani attacks roots of a large variety of ornamental shrubs and fruit trees, native or introduced. Others species are monophagous or oligophagous on introduced hosts: the tamarind seed borer Sitophilus linearis on Tamarindus indica, Demyrsus meleoides on cycadophyts, Scyphophorus acupunctatus on Agavaceae species, Phloeotribus liminaris on Prunus serotina, Phloeosinus rudis on Cupressaceae species.
Five species have an impact on forests or related habitats. Th ree attack live exotic or native trees. Th e Eucalyptus snout beetle Gonipterus scutellatus is an important pest of Eucalyptus everywhere it has been introduced (see factsheet 14.12). Th is defoliator causes severe damage and wood loss, particularly on E. globulus, the major cultivated Eucalyptus species in southern Europe. Rhyephenes humeralis attack another introduced tree, Pinus radiata, but causes less damage. Megaplatypus mutatus is one of the few platypodine beetles which breeds in live trees; it is highly polyphagous, but in Europe it has thus far only been found to damage Populus plantations in Italy (Alfaro et al. 2007). Th e two other species depreciate wood stock. Gnathotrichus materiarius is a common pest of a large variety of conifer wood, and Xylosandrus germanus sporadically attacks mainly broadleaf wood.
Pentarthrum huttoni and the two Euophryum species live in rotting wood, so their economic impact is generally low, though they do attack wood of historically signifi - cant artefacts or buildings. Finally, as opposed to all previous species, the introduced frond-feeding weevil Stenopelmus rufi nasus has a positive impact due to its hability to control the invasive red water fern Azolla fi liculoides.

Conclusion
Th e superfamily Curculionoidea is well represented among alien species now established in Europe. Alien weevils show specifi c characteristics comparing both native and world ones, which seem result from a selection of species having high capabilities to human-mediated dispersal and establishment in a new habitat. Th us, they have often cryptic habits, as seed boring or wood and plant boring, leading to over-representation of bark and ambrosia beetles and other xylophagous sensu lato 7 species; alien weevils are consequently more numerous in natural areas than other terrestrial invertebrate aliens. Seed feeders are the major alien pests. Alien species are mainly originated from Asia, which is related to the importance of trade with this continent, and many of them come from diff erent tropical or subtropical areas.
Th e more worrying observation is the fast increase in the invasion rate during last decades, as noticed for all terrestrial invertebrate aliens. Without appropriate control, the invasive pressure will probably continue to increase in the future, further threaten- ing European people and ecosystems, more especially as global warming may allow the naturalization of more tropical and subtropical species accidentally introduced into Europe and particularly the Mediterranean. Platypodines and scolytines adults generally feed as larvae, as do adults of many other species with spermatophagous or xylophagous sensu lato 7 larvae. Otherwise adults generally feed externally on leaf and stem regardless of the larval habits. Adults are often more polyphagous than larvae, except platypodines and scolytines.

Family / subfamily Species
Th e presence of X. xylographus on all Canary Islands species lists (Schedl et al. 1959, Oromi and Garcia 1995, Machado and Oromi 2000, Izquierdo et al. 2004, and the absence of X. saxesenii, seems to stem from an early mistaken treatment of X. saxesenii as a junior synonym of X. xylographus (Schedl 1970). To verify this, Kirkendall located one specimen recently determined as X. Xylographus (Oromi and Garcia 1995), and confi rmed that it is X. saxesenii.