Influence of urbanisation and plants on the diversity and abundance of aphids and their ladybird and hoverfly predators in domestic gardens

Urban gardens can harbour a high diversity of insects, which are critically important components of urban ecosystems.In this work, we investigate the richness and diversity of a major taxon of economic and ecological importance, the aphids (Hemiptera: Aphididae), and their main insect predators, the hoverfl ies (Diptera: Syrphidae) and ladybirds (Coleoptera: Coccinellidae), inurban gardens. We examined how variation in environmental factors associated with urbanisation (garden host plant abundance,garden plant richness, garden size, proportion of impervious surfaces in the surrounding area) directly and indirectly (via preyand predator abundance) infl uence the local diversity and abundance of aphids, ladybirds, and hoverfl ies. Sixty-seven domesticgardens located in southern England were surveyed during the peak period of aphid abundance, and the numbers and identityof aphids and their predators were recorded. We observed 45 aphid species (179917 individuals in total), 15 hoverfl y species(494 individuals) and 8 ladybird species (173 individuals). We found that aphid species richness and abundance were positivelyassociated with utilised host plant abundance and garden plant species richness. Hoverfl y abundance was positively correlatedwith garden plant richness. The abundance of ladybirds was positively correlated with aphid abundance and garden plant speciesrichness, and negatively associated to the proportion of impervious surfaces in the surrounding environment. The difference inresponses between the two major taxa of aphid predators may refl ect differences in their behaviour and natural history. Our resultsindicate that overall increases in urban land cover are not favourable for ladybirds as a group, and that fi ne scale habitat variablesthat are determined by garden owners have the potential to greatly affect the diversity of aphids and their primary predators.