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Abstract
We present a food-web study of the parasitoid wasps and their fly hosts found in the nests of cavity-nesting songbirds. This birds' nest parasitoid web is different from all parasitoid webs studied comprising exclusively non-phytophagous host species. A total of 490 nests were examined for host occurrence, abundance and parasitism rates. Thirty-two species of potential hosts and 10 species of parasitoid wasps were recorded in nests from 25 sites in northern Germany and from two additional sites in south-western Germany. Most of these species were rare and unspecialized. The only very common parasitoid was Nasonia vitripennis (Chalcidoidea: Pteromalidae). The records of 14 regular host species from northern Germany, which are connected to all 10 parasitoid species, were used for further calculation of food-web statistics. The parasitoid communities in birds' nests were compared with other known parasitoid communities. The birds' nests exhibited a lower species richness compared with communities of phytophagous hosts, but showed similarities with communities of necrophagous or coprophagous hosts, or of parasitoid hosts. The parasitism rate was comparable in all host–parasitoid-systems, supporting the idea that the parasitism rate is independent of species richness.
Acknowledgements
The authors would like to thank the numerous nest donors and individuals who gave access to nest boxes, especially Karl Staiber (Bad Arolsen) and Helmut and Frieder Klöpfer (Bad Mergentheim). We thank Bernhard Misof (Hamburg) for helpful comments on earlier drafts of this manuscript and Andrew Polaszek and an anonymous referee for reviewing the manuscript. We thank Kees van Achterberg (Nationaal Natuurhistorisch Museum, Leiden) for identification of Alysia manducator and Gérard Delvare (CIRAD, Montpellier) for his assessment of the Eurytoma sp.