Abstract
Urban gardens are a prominent part of agricultural systems, providing food security and access within cities; however, we still lack sufficient knowledge and general principles about how to manage pests in urban agroecosystems in distinct regions. We surveyed natural enemies (ladybeetles and parasitoids) and conducted sentinel pest removal experiments to explore local management factors and landscape characteristics that influence the provisioning of pest control services in California, USA, and Chiapas, Mexico. We worked in 29 gardens across the two locations. In each location, we collected data on garden vegetation, floral availability, ground cover management, and the percentage of natural, urban, and agricultural land cover in the surrounding landscape. We sampled ladybeetles, Chalcidoidea, and Ichneumonoidea parasitoids with sticky traps, and monitored the removal of three different pest species. Ladybeetle abundance did not differ between locations; abundance decreased with garden size and with tree cover and increased with herbaceous richness, floral abundance, and barren land cover. Chalcicoidea and Ichneumonoidea parasitoids were more abundant in Chiapas. Chalcicoidea abundance decreased with herbaceous richness and with urban cover. Ichneumonoidea abundance increased with mulch and bare ground cover, garden size, garden age, and with agriculture land cover but decreased with tree richness and urban cover. Predators removed between 15–100% of sentinel prey within 24 h but prey removal was greater in California. Generally, prey removal increased with vegetation diversity, floral abundance, mulch cover, and urban land cover, but declined with vegetation cover and bare ground. Although some factors had consistent effects on natural enemies and pest control in the two locations, many did not; thus, we still need more comparative work to further develop our understanding of general principles governing conservation biological control in urban settings.
Highlights
Scientists, peasant organizations, and the UN Food and Agriculture Organization recognize that agroecology is essential to the production of healthy, culturally appropriate and abundant food [1,2]
Understanding the relationships underlying biological pest management is especially critical for urban gardens, given that the alternative—the use of chemical pesticides—may be especially damaging or risky for human populations living in close proximity
Urban gardens may serve as a refuge for a high diversity of biological control agents such as ladybeetles, parasitic wasps, carabids, spiders, ants and syrphid flies [6,7]
Summary
Scientists, peasant organizations, and the UN Food and Agriculture Organization recognize that agroecology is essential to the production of healthy, culturally appropriate and abundant food [1,2]. Agroecological practices promote pest prevention in part by managing crop diversity and plot and landscape design to conserve and increase biological control agents [3,4]. Urban gardens may serve as a refuge for a high diversity of biological control agents such as ladybeetles, parasitic wasps, carabids, spiders, ants and syrphid flies [6,7]. Populations of pests and natural enemies respond to site and landscape factors [8], but comparative work exploring how these relationships vary among geographic regions has been lacking. Such studies are essential to advance the development of general principles of urban ecology [9]
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