Distribution and frequency of Culex pipiens and Culex torrentium (Culicidae) in Europe and diagnostic allozyme markers

The morphologically similar Culex pipiens sensu lato and Cx. torrentium are sympatric in much of Central, Eastern and Northern Europe. Since morphological separation of females of these mosquitoes is extremely difficult and uncertain, diagnosis depends upon time consuming microscopic examination of male hypopygial characters. Consequently the possible, or even probable, occurrence of Cx. torrentium has been ignored in numerous field studies which have recorded (perhaps erroneously) presence of Cx. pipiens only. As a consequence, knowledge of the true geographical distribution, frequency of occurrence and ecological characteristics of these mosquitoes is deficient or confused. In this study, the species diagnostic enzyme markers, adenylate kinase (AK) and 2hydroxybutyrate dehydrogenase (HBDH) were shown to discriminate between Cx. pipiens and Cx. torrentium larvae as well as male and female adults. Diagnostic allele and genotype differentiations were quantified. In total, 4,040 mosquitoes of Cx. pipiens sensu lato and Cx. torrentium from Germany and other countries were studied. Culex torrentium was shown to be frequently encountered in Central Europe. Though genetically and reproductively separated from Cx. pipiens, it exhibits similar ecological characteristics, and there is a high degree of association between these taxa in the breeding sites. Of 2052 specimens collected from ovitraps in South-West Germany, 54.8% were identified as Cx pipiens and 45.2% as Cx. torrentium. In 712 samples taken from natural and artificial breeding sites, 59% were identified as Cx. pipiens and 41% as Cx. torrentium. In contrast, of adult specimens caught in CO2-traps, only 3.9% were Cx. torrentium, and the other 96.1% were Cx. pipiens, indicating selective attraction exerted by the CO2-traps. Both species were also found in other parts of Germany. Neither Cx. torrentium nor Cx. quinquefasciatus were detected in samples obtained from Turkey, Cyprus, Greece, Serbia and South Eastern France, though all these contained Cx. pipiens. It was only in samples from Germany and Luxembourg that Cx. torrentium was frequent.