An entomological review of invasive mosquitoes in Europe.

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.

Changes in species richness and spatial distribution of mosquitoes (Diptera: Culicidae) inferred from museum specimen records and a recent inventory: a case study from Belgium suggests recent expanded distribution of arbovirus and malaria vectors.

Mosquito (Diptera: Culicidae) distribution data from a recent inventory of native and invading mosquito species in Belgium were compared with historical data from the period 1900-1960 that were retrieved from a revision of the Belgian Culicidae collection at the Royal Belgian Institute of Natural Sciences. Both data sets were used to investigate trends in mosquito species richness in several regions in Belgium. The relative change in distribution area of mosquito species was particularly important for species that use waste waters and used tires as larval habitats and species that recently shifted their larval habitat to artificial larval habitats. More importantly, several of these species are known as vectors of arboviruses and Plasmodium sp. and the apparent habitat shift of some of them brought these species in proximity to humans. Similar studies comparing current mosquito richness with former distribution data retrieved from voucher specimens from collections is therefore encouraged because they can generate important information concerning health risk assessment at both regional and national scale.

Nationwide inventory of mosquito biodiversity (Diptera: Culicidae) in Belgium, Europe.

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.

Bionomics of the established exotic mosquito species Aedes koreicus in Belgium, Europe.

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.

Human-induced expanded distribution of Anopheles plumbeus, experimental vector of West Nile virus and a potential vector of human malaria in Belgium.

For the majority of native species, human-created habitats provide a hostile environment that prevents their colonization. However, if the conditions encountered in this novel environment are part of the fundamental niche of a particular species, these low competitive environments may allow strong population expansion of even rare and stenotopic species. If these species are potentially harmful to humans, such anthropogenic habitat alterations may impose strong risks for human health. Here, we report on a recent and severe outbreak of the viciously biting and day-active mosquito Anopheles plumbeus Stephens, 1828, that is caused by a habitat shift toward human-created habitats. Although historic data indicate that the species was previously reported to be rare in Belgium and confined to natural forest habitats, more recent data indicate a strong population expansion all over Belgium and severe nuisance at a local scale. We show that these outbreaks can be explained by a recent larval habitat shift of this species from tree-holes in forests to large manure collecting pits of abandoned and uncleaned pig stables. Further surveys of the colonization and detection of other potential larval breeding places of this mosquito in this artificial environment are of particular importance for human health because the species is known as a experimental vector of West Nile virus and a potential vector of human malaria.

Introduction and establishment of the exotic mosquito species Aedes japonicus japonicus (Diptera: Culicidae) in Belgium.

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.

Identification of Belgian mosquito species (Diptera: Culicidae) by DNA barcoding.

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.