Biology of the parasitic wasp nest beetle, Metoecus paradoxus (Coleoptera: Ripiphoridae), in Finland
Parasitoids and predators can cause marked mortality in their host species. I studied the occurrence, abundance, and biology of the wasp nest beetle Metoecus paradoxus (Ripiphoridae), inhabiting the nests of the common wasp Vespula vulgaris (Vespidae) in Central Finland. I also compiled phenological data of the species in Finland. The proportion of parasitized nests was 80%. The abundance of the beetle was generally some tens of individuals (max. = 130) per nest, and the parasitism rate 1–18% of the sealed cells, which are typical for the species in temperate Europe. The beetle occurred in several combs but was absent or rare in the oldest and newest combs. Sex ratio was female biased. Females were larger than males, and individuals from large cells were larger than from small cells. Adult beetles were observed rather steadily from early August to late September. The study shows that M. paradoxus is a common inhabitant of V. vulgaris nests in Central Finland, but due to a low frequency of parasitized cells its impact on wasp populations is likely to be minor.