Factors restricting the abundance of wasp colonies of the European hornet <i>Vespa crabro</i> and the Saxon wasp <i>Dolichovespula saxonica</i> (Hymenoptera: Vespidae) in an urban area in Poland
Various factors affecting the reproductive success of Vespacrabro and Dolichovespula saxonica (Vespinae), including their parasitoids, parasites, pathogens and other micro organisms accompanying their nests in the city of Lódz in Poland were investigated. Sphecophaga vesparum, Aphomia sociella and especially Quedius brevicornis, whose larvae cause destruction of wasp nests, were recorded. Totally 19 species or groups of bacteria, including pathogens like Pseudomon aeruginosa, Enterobacter cloacae, Staphylococcus aureus and Enterococcus faecalis, and 5 species of fungi were identified. Cities create very good conditions for wasp societies. Unfortunately, their presence can cause specific but important risks to humans, which lead to massive destruction of wasp nests. However, this does not cause considerable decrease in the number of colonies of common wasp species but less abundant species may be endangered in cities by this practice. It is thus recommended to limit the number of all wasp nests destroyed and to discriminate between the species.