Ambrosiodmus rubricollis (Eichhoff, 1875)

Faccoli, Massimo, Frigimelica, Gabriella, Mori, Nicola, Toffolo, Edoardo Petrucco, Vettorazzo, Marco & Simonato, Mauro, 2009, First record of Ambrosiodmus (Hopkins, 1915) (Coleoptera: Curculionidae, Scolytinae) in Europe, Zootaxa 2303, pp. 57-60 : 57-59

Ambrosiodmus rubricollis (Eichhoff, 1875)

Diagnosis. Ambrosiodmus rubricollis is the only Ambrosiodmus species known to Europe, and it is easily distinguished from other European species of the tribe Xyleborini by the asperities covering the entire surface of the pronotum, where extend from anterior to base, including most of discal area ( Figs. 1 a, b) ( Wood 1986; Maiti & Saha 2004). Other features concern the antennal club, which has the first segment rounded on both faces ( Figs. 1 d, 2a), extending to subapical area of posterior face, and the second segment conspicuous on anterior face ( Rabaglia et al. 2006). The anterior margin of the pronotum is never armed by a definite row of serrations ( Figs. 1 a, b, d), whereas the lateral margins of protibiae and metatibiae are armed by 7–8 and 8–11 denticles, respectively ( Fig. 2 b). Females (2.4–2.7 mm) ( Fig. 1 a) are always larger than males (1.6–1.8 mm) ( Fig. 1 c).

Distribution. The species is widespread in Asia ( China, India, Japan, Korea, Malaysia, Taiwan, Thailand, Vietnam) ( Wood & Bright 1992). It was then introduced in Australia ( Wood & Bright 1992) and North America ( Bright 1968), where now it is commonly found in 11 mid-Atlantic and south-eastern states ( Rabaglia et al. 2006), indicating its quick spread into new regions, probably aided by its inbreeding mating system and its polyphagy ( Kirkendall & Jordal 2006).

Hosts. As for all Xyleborini , Ambrosiodmus species are ambrosia beetles ( Wood 1986). Ambrosiodmus rubricollis is extremely polyphagous on broadleaved trees and shrubs, and is occasionally reported also from conifers. The recorded host trees, arranged in alphabetical order, include: Abies fabri , Acacia sp., Alnus sibirica , Biota orientalis , Carya glabrata , Carya sp., Castanea sp., Cinnamomum sp., Cornus sp., Cunninghamia lanceolata , Diospyros kaki , Fraxinus chinensis , Hovea sp., Ilex sp., Juglans nigra , Ligustrum lucidum , Machilus sp., Morus alba , Myrica sp., Pinus merkusii , Populus sp., Prunus sp., Quercus sp., Rhus sp., Schima superba , Sophora japonica , Terminalia myriocarpa , Vitex negundo ( Wood 1986; Wood & Bright 1992; Bright & Skidmore 1997). The Italian records add horse chestnut ( Aesculus hippocastanum ).

Genetic analysis. Some individuals freshly collected from infested trees of Padova and Verona were singly stored in 70% ethanol until DNA extraction. Nucleic acid extraction was performed on single specimens following a salting out protocol ( Patwary et al. 1994). A segment of the mitochondrial COI gene was amplified using the universal primers HCO1490 and LCO2198 ( Folmer et al. 1994). The purified fragment was sent to sequencing with the HCO1490 primer at BMR Genomics, University of Padova. Finally, the sequence was submitted to GenBank with the accession number GQ331107 . The insects collected from the two localities belong to the same species, A. rubricollis , and they share the same haplotype.

As adults of A. rubricollis were found in three different localities separated by more than 100 km, and because the infested tree found in the botanic garden of Padova in spring 2009 was hosting overwintering adults, it is clear that the species is now established in Italy. This conclusion arises from the high number (thousand of individuals) of overwintering and breeding adults found in the infested trees in different localities. The first infested tree found (from Padova) was attacked in summer 2008 whereas the insect finding occurred in spring 2009, indicating the possibility for A. rubricollis to survive to the Italian winter. However, it is impossible to determine from where the species began to spread and how it reached Europe. The botanic garden of Padova has hundreds of woody plants from each continent, including species coming from the native regions of A. rubricollis (Asia) , or from territories where the insects has been introduced (North America). Nevertheless, it is more likely that A. rubricollis came to Europe with dead wood or wood packing material, rather that by purchase/exchange of exotic plants performed by the botanic garden, or by international trades of tree species. In this respect, the species was found very close to the international airport of Verona and in the international harbour of Venice. In both cases, the amount of exotic wood passing every year through these ports is very huge. An interesting question arises whether the species has been directly imported from the Orient, or secondarily from the USA. Future DNA analyses performed on different populations might sort this out.

Ambrosiodmus rubricollis joins eight other exotic ambrosia beetles established in Italy ( Xylosandrus germanus , X. crassiusculus , X. morigenus , Monarthrum mali , Xyleborus atratus , X. affinis , X. pfeilii and Gnathotrichus materiarius ) in the last decades (Kirkendall & Faccoli, submitted). Although A. rubricollis cannot be considered an aggressive species, because it develops only in dead wood, it can be regarded as an invasive species with a very high expansion rate, spreading in 11 US states in less than 40 years. In this respect, the New Zealand National Plant Protection Organisation reports A. rubricollis among the species submitted to measures to prevent their entry and establishment. Such measures include visual inspection of produces and associated packaging, and treat, reship or destroy of the consignments in case of interception ( Herrera 2005). A successful colonisation of new territories has also been correlated with polyphagy, as recorded in A. rubricollis and in many other wood-boring insects moving among continents ( Ric et al. 2007). Thus, reporting the first finding of Monarthrum mali in Europe, Kirkendall et al. (2008) attributed the success of ambrosia beetles as alien species to their lack of host specialization. In addition, as for all Xyleborini , Ambrosiodmus species inbreed ( Wood 1986; Kirkendall & Jordal 2006); newly matured females mate with siblings before emerging from the host ( Kirkendall 1983), and the establishment of new populations can occur also from very few individuals ( Jordal et al. 2001). The high proportion of females emerging from the infested wood reflects this reproductive system.

Nothing is known about how widespread the Italian population of A. rubricollis occurs, nevertheless we know nothing that could hinder the species spreading throughout Italy and eventually Europe. Scolytids considered as harmless in their native countries occasionally can become aggressive pests into new territories ( Atkinson et al. 1990; Knizek 2007). The strong infestation recorded in the peach orchard close to Verona could be a first indicator of the potential harmfulness of this exotic species acclimatised in a new continent. A specific monitoring program would be necessary to establish the real distribution of A. rubricollis and the occurrence of other exotic bark and ambrosia beetles in Europe.

Figures

FIGURE 1. Ambrosiodmus rubricollis (Eichhoff, 1875): a, female, dorsal habitus; b, female pronotum, dorsal view; c, male, dorsal habitus; d, female pronotum, lateral view.

FIGURE 2. Ambrosiodmus rubricollis (Eichhoff, 1875): a, antenna, showing anterior face of club; b, protibia.