Edmondson, J. L. | Search bioRxiv

bioRxiv2025

Experimental wildflower additions increase pollination in urban agroecosystems

O_LIThe addition of nectar-rich flower patches in human-modified ecosystems is a common practice to mitigate pollinator declines and boost pollination. However, the benefits of these additions for pollinator communities and pollination services are rarely tested, especially in urban environments. C_LIO_LIIn a city-scale experiment we added floral resources to urban allotments and monitored the effects on bees, hoverflies and moths, and tested for improved seed set in a model crop (tomato, Solanum lycopersicum). C_LIO_LIThe addition of wildflowers did not benefit all insect communities. Only social bee abundance (Bombus and Apis) benefitted from increasing floral resource area whereas other insect taxa showed no changes in abundance potentially due to the divergence in foraging patterns of moths, hoverflies, social bees and solitary bees. The addition of wildflower patches enhanced pollination by supporting a 25.3% increase in tomato seed set, providing evidence that wildflower interventions can improve urban pollination. Seed set was higher in more urban sites, suggesting an "oasis effect" where pollinating insects are concentrated into limited greenspaces. This highlights the precarity of pollination services in highly urban areas. C_LIO_LIOur results suggest that the practice of planting wildflower patches can positively affect pollination services in urban areas. The continued promotion of flower patch addition is likely to benefit some key insect taxa, however, the common wildflower species in seed mixes may not benefit hoverflies and moths compared to bees. The taxon-specific foraging patterns we observed should inform the design and development of pollinator-friendly wildflower seed mixes. C_LI Societal impact statementEnhancing urban greenspaces for pollinator communities by planting wildflower patches is increasingly common, but their efficacy for different groups of insects (bees, hoverflies and moths) is unclear. Our city-scale experiment demonstrated that wildflower patches benefitted the abundance of social bees, but did not increase other groups. Wildflower addition increased pollination services, with an increase in seed-set in our model crop, particularly in more urban areas. Wildflower patches do benefit pollinator communities and in turn humans, through the pollination services, but the species mix may not benefit some insect groups. This suggests there is potential to improve the benefit provided by wildflower patches by redesigning pollinator-friendly seed mixes.

ecology↗

bioRxiv2024

Supplementing floral resources does not mitigate the negative effects of urbanisation on cavity-nesting bees and wasps.

O_LICavity-nesting bees and wasps provide essential ecosystem services such as pollination and pest control. Within urban environments, it is likely that cavity-nesting insects are using greenspaces to forage for food and nesting resources, and thus may benefit from urban greenspace management interventions, such as the addition of flower patches and "bee hotels" (trap nests). C_LIO_LIIn contrast to the relatively large body of work demonstrating the effects of wildflower provisioning on bees in an agricultural context, there have been few studies testing the benefits of floral provisioning, or the relative importance of nest site and food constraints on urban cavity-nesting bees and wasps. Consequently, we lack an empirical evidence base for optimising and informing conservation interventions for these taxa. C_LIO_LITo understand how the addition of floral resources influences cavity-nesting insect communities, we conducted a 2-year study in urban greenspaces used for horticulture (allotments). We manipulated floral and nesting resources by adding nectar-rich flower patches and artificial trap nests, and compared nest colonisation by cavity-nesting bees and wasps in sites with floral additions and where no additions were made. Our sites were configured along an urbanisation gradient, allowing us to examine how surrounding urbanisation influenced these patterns. C_LIO_LIContrary to our predictions, we found no significant difference in trap nest uptake in sites where floral resources were added, compared to control sites. However, cavity-nesting insect abundance showed a 6-fold decrease over our urbanisation gradient. The addition of floral resources did not mitigate the negative effects of urbanisation on cavity-nesting insects. C_LI Synthesis and Applications: Although enhancing floral resources in urban systems is a recognised strategy for conserving key pollinators such as social bees, our findings suggest that this approach alone does not address the challenges faced by cavity-nesting bees or wasps in urban landscapes. Our results suggest that accounting for the diversity of resource requirements and incorporating landscape-scale analysis is essential to ensure local conservation interventions will benefit a diversity of insect communities.

ecology↗