Culicidae (Diptera) in the diet of predatory stages of anurans (Amphibia) in humid biotopes of the Rhine Valley in Germany

A three-year field study was conducted during 1993 to 1995 to determine the importance of mosquitoes in the diet of anurans. The study was aimed to assess the impact of biological mosquito control on the populations of amphibia in the Rhine Valley, Germany. Sampling took place in two areas with stands of different deciduous trees at the western bank of the Rhine (north of Karlsruhe, Germany) from early May to late October. The frequency and species composition of the terrestrial stages of Amphibia was monitored by hand catches and by live pitfall trapping. A total of 2,419 Amphibia were caught in the three years. Of these, 95.8% were anurans, consisting of 77% Ranidae, with 25.5% Rana arvalis, and 4.2% were Urodela, Salamandridae. All anura caught were subjected to "stomach flushing" to yield their stomach contents before they were released again. The stomachs of 2,163 anuran specimens contained an average of 7.7 prey items, of which only 0.16% were Culicidae. In R. arvalis the total diet consisted of 33% Collembola, spiders and beetles; 0.1% of the specimens in the diet were Culicidae. The most common culicid species in the study area, Aedes vexans, was also most often found in the anuran stomachs. However, no correlation existed between the number of mosquitoes and their number as prey of Anura. It is concluded that anurans will not be negatively affected by biological mosquito control in the Rhine Valley. Furthermore, the impact of anurans on Culicidae seems to be negligible.