Sessions

Wasps play an essential role in ecosystem services, particularly biological control through predation and parasitoidism, as well as pollination. They are severely understudied, and we know little about how they respond to urbanisation, a prominent driver of recent entomofauna loss. Therefore, in this study, we focused on how urbanisation affects cavity-nesting solitary wasps. For this, we used trap nests, a powerful tool to study abundance, species richness, prey composition and natural enemies, and compared four habitat types: urban parks, suburban parks, forest edges and agricultural field margins, with the former two representing different extents of urbanisation, and the latter two serving as control areas. We sampled eight Hungarian cities: Debrecen, Kaposvár, Miskolc, Pécs, Szombathely, Tatabánya, Veszprém and Zalaegerszeg.

We investigated the effect of urbanisation on total abundance and the abundance of the three feeding guilds: herbivore hunters, spider hunters, and parasitoids of other cavity-nesting Hymenopterans, alongside total species richness. Local diversity was assessed based on species richness and abundance, while differences in community composition between habitat types were examined using PERMANOVA. In addition, a food-web analysis was conducted to assess linkage density and Shannon’s diversity index between cavity-nesting wasps and their parasitoids in each habitat type, as indicators of food-web complexity. Lastly, we studied the host composition of the spider-hunting Trypoxylon species, whose prey mostly consisted of adult female or juvenile spiders, and investigated whether there was any pattern of preference towards either of the two in any of the habitats.

Our results show that in all aspects, the urban parks appear to be substantially more disturbed than all of the other habitats: they had the lowest abundances in case of both total and feeding guild abundances, the lowest species richness, as well as the least complex food-web. However, we found no significant difference between the habitats regarding community composition. As for the prey composition of the Trypoxylon species, we found that in urban parks there was an overwhelming preference for the adult female spiders, whereas field margins had more juveniles, despite other studies reporting a general preference towards juveniles. We hypothesised that this may be a consequence of the disturbance of the urban landscape, probably resulting in less ideal reproductive conditions for the spiders.

As this study mainly focused on determining whether urbanisation has any notable effects on cavity-nesting wasps, we examined this effect in a combined manner, without placing much emphasis on the individual factors that may cause decline in urban areas. Therefore, we could only formulate hypotheses, which may serve as topics of interest for further research, not only to understand why wasps are declining, but what we could do to conserve them.