Gert van der Hoek
In Memoriam - Editor, Senior Moderator
Journal of Vector Ecology 35(1):210-212. 2010
First Evidence for Presence of Culex pipiens Biotype Molestus in the Netherlands, and of Hybrid Biotype Pipiens and Molestus in Northern Europe
Mosquitoes (Diptera: Culicidae) are the principal vectors of West Nile virus (WNV). The likely introduction pathway of WNV into northwestern Europe is by infected migratory birds from WNV-endemic regions like Africa and central Europe.
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RESULTS AND DISCUSSION
A total of 29 adult specimens, collected at three different underground stations in Amsterdam were morphologically identified as members of the Cx. pipiens complex and were further typed by PCR. Figure 1 shows a typical result for typing Cx. pipiens specimens at the biotype level (Bahnck and Fonseca 2006). Of the analyzed specimens, two were identified as biotype pipiens, 18 specimens as biotype molestus, and nine specimens as hybrid forms. These results were confirmed by sequencing of the PCR products from two biotype molestus specimens, one biotype pipiens specimen, and two hybrid specimens. No other polymorphisms were observed in the amplified region of the CQ11 gene (data not shown).
In this study, we provide the first evidence for the presence of Cx. pipiens b. molestus and b. pipiens hybrids in northern Europe and Cx. pipiens b. molestus in the Netherlands. Interestingly, the different biotypes and hybrids co-existed in the same underground breeding sites.
Sympatric occurrence of biotype molestus and pipiens in surface habitats has been observed before in southern Europe and the U.S.A. (Chevillon et al. 1995, Fonseca et al. 2004, Gomes et al. 2009) but never for underground habitats as observed in this study.
The distinction among the members of the Cx. pipiens complex is essential for understanding local WNV epidemiology. The two biotypes and hybrid form of the Cx. pipiens complex are thought to have different feeding preferences and, consequently, different vectorial capacities. Observations on hybrids in the U.S.A. suggest a genetic basis for feeding preferences of members of the Cx. pipiens complex.
Biotype pipiens females that fed upon mammals, in particular humans, had a significantly higher proportion of biotype molestus ancestry than females that fed upon birds (Huang et al. 2008, Kilpatrick et al. 2007). In the field, hybrids appeared to bite readily both humans and birds as an opportunistic feeder (Fonseca et al. 2004).
Therefore, hybrids between the molestus and pipiens biotypes may act as bridge vectors with a major contribution to human WNV epidemiology. It has been hypothesized that the presence of these opportunistic feeders in the Cx. pipiens complex in combination with a susceptible bird population and highly concentrated human populations have created conditions for human epidemics. This is illustrated by the rapid spread and severity of the WNV epidemic in the U.S.A. since 1999 (Fonseca et al. 2004).
By analogy with the circumstances in North America, the presence of hybrids in northern Europe might be an important determinant for the dynamics of WNV in northern Europe. For risk assessment purposes, information on the geographic distribution, proportion within the Cx. pipiens complex population, and phenotypic properties of the European (Dutch) hybrids in more detail is essential.
The public transport company has intensified the treatments and is improving the basins built in order to prevent development of larvae and possible entrance or escape of adults.
Full article
First Evidence for Presence of Culex pipiens Biotype Molestus in the Netherlands, and of Hybrid Biotype Pipiens and Molestus in Northern Europe
Mosquitoes (Diptera: Culicidae) are the principal vectors of West Nile virus (WNV). The likely introduction pathway of WNV into northwestern Europe is by infected migratory birds from WNV-endemic regions like Africa and central Europe.
- snip -
RESULTS AND DISCUSSION
A total of 29 adult specimens, collected at three different underground stations in Amsterdam were morphologically identified as members of the Cx. pipiens complex and were further typed by PCR. Figure 1 shows a typical result for typing Cx. pipiens specimens at the biotype level (Bahnck and Fonseca 2006). Of the analyzed specimens, two were identified as biotype pipiens, 18 specimens as biotype molestus, and nine specimens as hybrid forms. These results were confirmed by sequencing of the PCR products from two biotype molestus specimens, one biotype pipiens specimen, and two hybrid specimens. No other polymorphisms were observed in the amplified region of the CQ11 gene (data not shown).
In this study, we provide the first evidence for the presence of Cx. pipiens b. molestus and b. pipiens hybrids in northern Europe and Cx. pipiens b. molestus in the Netherlands. Interestingly, the different biotypes and hybrids co-existed in the same underground breeding sites.
Sympatric occurrence of biotype molestus and pipiens in surface habitats has been observed before in southern Europe and the U.S.A. (Chevillon et al. 1995, Fonseca et al. 2004, Gomes et al. 2009) but never for underground habitats as observed in this study.
The distinction among the members of the Cx. pipiens complex is essential for understanding local WNV epidemiology. The two biotypes and hybrid form of the Cx. pipiens complex are thought to have different feeding preferences and, consequently, different vectorial capacities. Observations on hybrids in the U.S.A. suggest a genetic basis for feeding preferences of members of the Cx. pipiens complex.
Biotype pipiens females that fed upon mammals, in particular humans, had a significantly higher proportion of biotype molestus ancestry than females that fed upon birds (Huang et al. 2008, Kilpatrick et al. 2007). In the field, hybrids appeared to bite readily both humans and birds as an opportunistic feeder (Fonseca et al. 2004).
Therefore, hybrids between the molestus and pipiens biotypes may act as bridge vectors with a major contribution to human WNV epidemiology. It has been hypothesized that the presence of these opportunistic feeders in the Cx. pipiens complex in combination with a susceptible bird population and highly concentrated human populations have created conditions for human epidemics. This is illustrated by the rapid spread and severity of the WNV epidemic in the U.S.A. since 1999 (Fonseca et al. 2004).
By analogy with the circumstances in North America, the presence of hybrids in northern Europe might be an important determinant for the dynamics of WNV in northern Europe. For risk assessment purposes, information on the geographic distribution, proportion within the Cx. pipiens complex population, and phenotypic properties of the European (Dutch) hybrids in more detail is essential.
The public transport company has intensified the treatments and is improving the basins built in order to prevent development of larvae and possible entrance or escape of adults.
Full article