Research & reports

Emilie E. Ellis, S. Campbell, Jill L. Edmondson · Proceedings of the Royal Society B Biological Sciences · Global

A large-scale assessment across three cities found up to a 43% reduction in species richness of bees, hoverflies, and nocturnal moths in urban horticultural sites along urbanization gradients. These declines are driven by taxon-specific landscape changes like reduced tree canopy and semi-natural habitat. Moths and hoverflies were particularly sensitive to urbanization compared to bees, indicating a wide range of pollinators are under threat in urban landscapes.

Johanna Bock, Márcio Zamboni Neske, Martin Krauß, Andrea Dombrowski, Jörg Oehlmann · Environmental Sciences Europe · Europe

Focusing on small water bodies in private urban gardens, this study examined whether chemical pollution limits insect diversity, given that gardens make up a significant share of urban green area and can serve as important habitats and stepping stones for insects, while pesticides, fertilizers and chemical run-off from building materials can strongly affect habitat quality and insect biodiversity. Garden pond toxicity was assessed using in vitro and in vivo methods and chemical screening. Of 17 ponds examined, only one water sample and one sediment sample were found non-toxic in a bioluminescence assay with Aliivibrio fischeri. Enhanced dioxin-like activity was measured in seven water and ten sediment samples using a reporter gene assay with Saccharomyces cerevisiae, and most water extracts showed mutagenic potential in the Ames fluctuation assay (Salmonella typhimurium strains YG1041 and YG1042), while most sediment extracts were not mutagenic. Increased larval mortality of Chironomus riparius occurred in five water-sediment systems built from pond samples, correlating positively with in vitro water toxicity and with concentrations of benzothiazole derivatives measured by LC-HRMS, likely originating from EPDM rubber pond liners. Substance composition differed significantly between house and allotment gardens, with higher concentrations measured in allotment ponds. The study concludes that chemical pollution in private urban gardens may have been underestimated to date, and that pond toxicity can severely affect insect populations, warranting further study.

Joan Casanelles‐Abella, Simone Fontana, Bertrand Fournier, David Frey, Marco Moretti · Ecological Applications · Switzerland (Zurich)

This study in 23 urban gardens in Zurich, Switzerland, examined feeding niche partitioning between wild bees and honeybees. Researchers found that feeding niche partitioning increased with wild bee species richness and in sites with lower landscape-scale resource availability, which also had lower honeybee abundances. However, beekeeping intensity at local and landscape scales did not directly influence community feeding niche partitioning or wild bee species richness, suggesting direct competition for resources was not a main driver for the wild bee community.

Kit Prendergast · Pacific Conservation Biology · Australia

The African carder bee, Pseudoanthidium (Immanthidium) repetitum, first recorded in Queensland in 2000, has now been found in Western Australia, marking a significant distribution expansion. Three confirmed and one unconfirmed localities were identified in the Mandurah region, with abundant female specimens observed in one garden. The presence of this introduced species necessitates vigilance due to known negative impacts on native fauna and flora.

J. Scott MacIvor, Laurence Packer · PLoS ONE · Global

This study modeled the occupancy probability of six solitary bee species using nest boxes set along an urbanization gradient over three consecutive years. Native M. pugnata showed decreased occupancy with increasing building footprint, and a similar but not significant pattern was found for native O. pumila. Conversely, introduced M. rotundata and M. centuncularis, along with native M. campanulae, exhibited increased occupancy with rising urbanization.

Amanda E. Nelson, Andrew A. Forbes · PLoS ONE · Global

This study sampled two plant-herbivore-parasitoid systems across 250 sites in a 360 km2 urban/agricultural landscape to investigate the impact of human development on trophic interactions. It found that herbivorous insect densities were decoupled from host tree densities in urban landcover types at several spatial scales. Furthermore, a parasitoid species was absent from all urban/suburban landcover in one system, even where its herbivore host was common, indicating that human land use patterns limit specialist insect distributions due to dispersal constraints.

Karin Ahrné, Jan Bengtsson, Thomas Elmqvist · PLoS ONE · Sweden (Stockholm)

This study investigated bumble bees in allotment gardens along an urbanization gradient from inner Stockholm to rural areas. Findings showed that bumble bee diversity decreased with increasing urbanization, from approximately eight species in rural areas to five to six species in urban allotment gardens. Higher variability in the abundance of certain species in the most urban areas suggested a potentially weaker reliability of the pollination ecosystem service in areas strongly influenced by human activity.