There has been growing interest in Europe in recent years in the establishment and spread of invasive mosquitoes, notably the incursion of Aedes albopictus through the international trade in used tires and lucky bamboo, with onward spread within Europe through ground transport. More recently, five other non-European aedine mosquito species have been found in Europe, and in some cases populations have established locally and are spreading. Concerns have been raised about the involvement of these mosquito species in transmission cycles of pathogens of public health importance, and these concerns were borne out following the outbreak of chikungunya fever in Italy in 2007, and subsequent autochthonous cases of dengue fever in France and Croatia in 2010. This article reviews current understanding of all exotic (five introduced invasive and one intercepted) aedine species in Europe, highlighting the known import pathways, biotic and abiotic constraints for establishment, control strategies, and public health significance, and encourages Europe-wide surveillance for invasive mosquitoes.

Among the invasive mosquitoes registered all over the world, Aedes species are particularly frequent and important. As several of them are potential vectors of disease, they present significant health concerns for 21st century Europe. Five species have established in mainland Europe, with two (Aedes albopictus and Aedes japonicus) becoming widespread and two (Ae. albopictus and Aedes aegypti) implicated in disease transmission to humans in Europe. The routes of importation and spread are often enigmatic, the ability to adapt to local environments and climates are rapid, and the biting nuisance and vector potential are both an ecomonic and public health concern. Europeans are used to cases of dengue and chikungunya in travellers returning from the tropics, but the threat to health and tourism in mainland Europe is substantive. Coupled to that are the emerging issues in the European overseas territorities and this paper is the first to consider the impacts in the remoter outposts of Europe. If entomologists and public health authorities are to address the spread of these mosquitoes and mitigate their health risks they must first be prepared to share information to better understand their biology and ecology, and share data on their distribution and control successes. This paper focusses in greater detail on the entomological and ecological aspects of these mosquitoes to assist with the risk assessment process, bringing together a large amount of information gathered through the ECDC VBORNET project.

The establishment of the potential vector species Aedes (Finlaya) japonicusjaponicus (Theobald) (Diptera: Culicidae) in southern Belgium is reported. The species was most likely introduced through the international trade in used tires. It was first collected in 2002 on the premises of a second-hand tire company and was sampled using different sampling methods in the two consecutive years (2003-2004). It was only in 2007 and 2008, during a national mosquito survey (MODIRISK), that its presence as adults and larvae at the above-mentioned site and at another tire company in the area was confirmed based on morphological and molecular identification. This discovery is the first record for Belgium of an exotic mosquito species that established successfully and raises the question on the need for monitoring and control. Considering the accompanying species found during the surveys, we also report here the first observation of Culex (Maillotia) hortensis hortensis (Ficalbi) in Belgium.

Adults of an exotic mosquito, Aedes (Finlaya) koreicus (Edwards) (Diptera: Culicidae) were identified by morphology and genotyping from one site in Belgium in 2008. In late summer of that year, the occurrence of adults and immature stages reconfirmed its presence. This is the first record of this species outside its native range and in particular in Europe. Two subsites of the original location were prospected from April until October 2009 with different traps to evaluate the extent of its presence and establishment in the area and to understand the dynamics of the species' population. Next to Ae. koreicus, 15 other mosquito species were collected. Adult individuals of Ae. koreicus were found from May to September and larvae were still found early October. Larvae were mainly retrieved from artificial containers both in 2008 as in 2009. Containers with eggs and/or larvae were found up to 4 km away from the initial location, indicating the species is spreading locally. Though the introduction route is unknown, it may have occurred via international trade as a large industrial center was located nearby. A comparison of different climatic variables between locations in Belgium with Ae. koreicus and putative source locations in South Korea, revealed similarities between winter temperatures and the number of freezing days and nights in four consecutive years (2004-2008), while humidity and precipitation values differed strongly. The introduction of a new potential disease vector into Europe seems to be a result of proper entrance points, created by intense worldwide trade and suitable environmental conditions.

To advance our restricted knowledge on mosquito biodiversity and distribution in Belgium, a national inventory started in 2007 (MODIRISK) based on a random selection of 936 collection points in three main environmental types: urban, rural and natural areas. Additionally, 64 sites were selected because of the risk of importing a vector or pathogen in these sites. Each site was sampled once between May and October 2007 and once in 2008 using Mosquito Magnet Liberty Plus traps. Diversity in pre-defined habitat types was calculated using three indices. The association between species and environmental types was assessed using a correspondence analysis. Twenty-three mosquito species belonging to traditionally recognized genera were found, including 21 indigenous and two exotic species. Highest species diversity (Simpson 0.765) and species richness (20 species) was observed in natural areas, although urban sites scored also well (Simpson 0.476, 16 species). Four clusters could be distinguished based on the correspondence analysis. The first one is related to human modified landscapes (such as urban, rural and industrial sites). A second is composed of species not associated with a specific habitat type, including the now widely distributed Anopheles plumbeus. A third group includes species commonly found in restored natural or bird migration areas, and a fourth cluster is composed of forest species. Outcomes of this study demonstrate the effectiveness of the designed sampling scheme and support the choice of the trap type. Obtained results of this first country-wide inventory of the Culicidae in Belgium may serve as a basis for risk assessment of emerging mosquito-borne diseases.

Since its introduction in 2003, DNA barcoding has proven to be a promising method for the identification of many taxa, including mosquitoes (Diptera: Culicidae). Many mosquito species are potential vectors of pathogens, and correct identification in all life stages is essential for effective mosquito monitoring and control. To use DNA barcoding for species identification, a reliable and comprehensive reference database of verified DNA sequences is required. Hence, DNA sequence diversity of mosquitoes in Belgium was assessed using a 658 bp fragment of the mitochondrial cytochrome oxidase I (COI) gene, and a reference data set was established. Most species appeared as well-supported clusters. Intraspecific Kimura 2-parameter (K2P) distances averaged 0.7%, and the maximum observed K2P distance was 6.2% for Aedes koreicus. A small overlap between intra- and interspecific K2P distances for congeneric sequences was observed. Overall, the identification success using best match and the best close match criteria were high, that is above 98%. No clear genetic division was found between the closely related species Aedes annulipes and Aedes cantans, which can be confused using morphological identification only. The members of the Anopheles maculipennis complex, that is Anopheles maculipennis s.s. and An. messeae, were weakly supported as monophyletic taxa. This study showed that DNA barcoding offers a reliable framework for mosquito species identification in Belgium except for some closely related species.

In 2008, specimens resembling Aedes (Finlaya) koreicus (Edwards) (also Ochlerotatus koreicus or Hulecoeteomyia kore-ica) were found in Belgium during a national mosquito survey (MODIRISK). Small but consistent differences were, how-ever, observed between the specimens described from Peninsula Korea and those found in Belgian. To achieve the correctidentification a detailed morphological comparison was made between the Belgian specimens and reference material fromKorean mainland and island populations housed at the Smithsonian Institution (Walter Reed Biosystematics Unit (WR-BU), Washington, USA). The identification was furthermore supported by molecular evidence based on the ND4 region(mtDNA) of available Korean and Belgian mosquito specimens. Morphological and molecular comparison confirmed theinitial identification of Aedes koreicus. Based on morphological characteristics, the species collected in Belgium mostlikely originated from Jeju-do, an island south of the Korean Peninsula. The observed dissimilarities between Korean andBelgian specimens resembled a number of morphological differences mentioned previously between female adults col-lected on the Korean Peninsula and Jeju-do. This is the first report of Aedes koreicus outside its natural distribution range.A correct and rapid identification of new invading and spreading vector species is crucial for the implementation of effec-tive control measurements. Hence a correct and easy accessible description of all possible variations of species arrivingin new areas is highly recommended. Therefore, a comparative morphological study on the Smithsonian material of thespecies from Korean mainland, island population and from Belgium is given, pictures of the main aberrant characteristicsand scanning electron microscope images of all stages of the species are included and molecular confirmation of the identification based on the mtDNA ND4 region is provided.

BackgroundThe tick species Ixodes ricinus and I. persulcatus are of exceptional medical importance in the western and eastern parts, respectively, of the Palaearctic region. In Russia and Finland the range of I. persulcatus has recently increased. In Finland the first records of I. persulcatus are from 2004. The apparent expansion of its range in Finland prompted us to investigate if I. persulcatus also occurs in Sweden.MethodsDog owners and hunters in the coastal areas of northern Sweden provided information about localities where ticks could be present. In May-August 2015 we used the cloth-dragging method in 36 localities potentially harbouring ticks in the Bothnian Bay area, province Norrbotten (NB) of northern Sweden. Further to the south in the provinces Västerbotten (VB) and Uppland (UP) eight localities were similarly investigated.Results Ixodes persulcatus was detected in 9 of 36 field localities in the Bothnian Bay area. Nymphs, adult males and adult females (n = 46 ticks) of I. persulcatus were present mainly in Alnus incana - Sorbus aucuparia - Picea abies - Pinus sylvestris vegetation communities on islands in the Bothnian Bay. Some of these I. persulcatus populations seem to be the most northerly populations so far recorded of this species. Dog owners asserted that their dogs became tick-infested on these islands for the first time 7–8 years ago. Moose (Alces alces), hares (Lepus timidus), domestic dogs (Canis lupus familiaris) and ground-feeding birds are the most likely carriers dispersing I. persulcatus in this area. All ticks (n = 124) from the more southern provinces of VB and UP were identified as I. ricinus.ConclusionsThe geographical range of the taiga tick has recently expanded into northern Sweden. Increased information about prophylactic, anti-tick measures should be directed to people living in or visiting the coastal areas and islands of the Baltic Bay.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1658-3) contains supplementary material, which is available to authorized users.