Biological Control of Aphids in Spain’s Urban Green Spaces

Green spaces in urban areas, such as parks and gardens, provide recreational, social, and health benefits for more than half of the world’s inhabitants. Arthropods in urban vegetation may cause some disruption to humans but also provide vital ecological services such as biological control and pollination. However, little is known about the ecology of urban pests, their natural enemies, and how to manage them in an ecofriendly manner, especially in Southern Europe. In this review article, we consider the information available concerning the biological control of aphids in the urban green areas of Spain, mainly focusing on the different aphid species, their natural enemies (and how to enhance them), and the sampling methods used to study them. A wide range of aphid species is found in Spain, but only a few are responsible for the majority of damage (so-called k-aphids, most of which are holocyclic species), and these show two distinct injury profiles (short and long) that determine monitoring and control strategies. Urban aphids have numerous natural enemies, including more than 20 species of ladybeetles, as well as predatory hoverflies, midges, lacewings, bugs, and other groups. More than 40 species of aphid parasitoids and their tritrophic aphid plant associations have been reported. The availability and usefulness of commercially reared aphid natural enemies is discussed, and two methods to enhance natural enemies are described. We also review aphid sampling methods developed for urban green spaces. The studies provide basic information on the ecology of aphids to support conservation biological control as a reliable strategy in the urban green areas of Spain.