Local and Landscape Effects to Biological Controls in Urban Agriculture-A Review

Predatory Arthropods Associated with the Invasive Tipu Psyllid, Platycorypha nigrivirga, in Southern Spain

Platycorypha nigrivirga Burckhardt (Hemiptera: Psyllidae) is a neotropical invasive species strictly associated with the tipu tree, Tipuana tipu (Benth.) Kuntze (Fabaceae: Papilionoideae). This psyllid has rapidly spread to several temperate areas of Spain and Portugal causing considerable problems in urban landscapes. The aim of this study was to determine the arthropod predator complex of this exotic insect and report the possibility of its biological control. Three urban green areas were surveyed in southern Spain during 2018 and 2019. Platycorypha nigrivirga populations increased during the spring months and reached a maximum level between late May and mid-June, declining greatly during the summer. A large complex of generalist predator species was found to exert a certain natural control on the pest, belonging to Anthocoridae (68.53%), Coccinellidae (18.39%), Chrysopidae (5.67%), Miridae (4.39%) and Araneae (3.02%). Anthocoris nemoralis (Fabricius) (Hemiptera: Anthocoridae) was the most abundant predatory species, followed by Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) and Scymnus laetificus Weise (Coleoptera: Coccinellidae). High levels of abundance of anthocorids coincided with the highest abundance of the pest, showing a significant relationship with the psyllid density. Anthocoris nemoralis seems to be a promising candidate to control P. nigrivirga in the urban green areas of southern Spain, but more studies are needed to define the optimum management strategies.

Multiple ecosystem service synergies and landscape mediation of biodiversity within urban agroecosystems

Ecosystem services (ESs) are essential for human well-being, especially in urban areas where 60% of the global population will live by 2030. While urban habitats have the potential to support biodiversity and ES, few studies have quantified the impact of local and landscape management across a diverse suite of services. We leverage 5 years of data (>5000 observations) across a network of urban community gardens to determine the drivers of biodiversity and ES trade-offs and synergies. We found multiple synergies and few trade-offs, contrasting previous assumptions that food production is at odds with biodiversity. Furthermore, we show that natural landscape cover interacts with local management to mediate services provided by mobile animals, specifically pest control and pollination. By quantifying the factors that support a diverse suite of ES, we highlight the critical role of garden management and urban planning for optimizing biodiversity and human benefit.

Biological Control Services from Parasitic Hymenoptera in Urban Agriculture

Simple Summary

Our findings support the enemies hypothesis in urban agroecosystems. Local factors, including increased mulch coverage, crop richness, and percent of non-crop areas, are predictors of increased PH abundance and aphid parasitism rates. Our findings support and strengthen previous findings in UA research. Urban farmers should be encouraged to diversify urban agroecosystem spatial composition and implement APM practices to reduce pest impacts.

Abstract

Urban agriculture is practiced in spatially fragmented landscapes with unique characteristics that can impact species occurrence in time and space. As a result, biological control services, an ecosystem service from naturally occurring arthropod natural enemies, can be negatively impacted. Many urban farms forgo pesticides and utilize agroecological pest-management strategies that rely on natural enemies to help regulate pest populations. Understanding how these enemies are affected by landscape composition and on-farm management practices is critical to understanding agroecological pest management in UA and furthering our understanding of landscape-mediated population dynamics. Over two growing seasons, we sampled brassica crops in urban agriculture sites occurring on a spectrum of surrounding landscape imperviousness, spatial composition, size, and management practices to better understand parasitic Hymenoptera abundance, richness, and parasitism rates on the common cabbage aphid (Brevicoryne brassicae). We found that on-farm agroecological pest-management practices such as mulch coverage, floral richness, and overall crop-plant richness impacted parasitic Hymenoptera abundance. Larger proportions of on-farm noncrop area increased parasitoid abundance on urban farms. Aphid parasitism increased in relation to on-farm management practices, including increased crop-plant richness. These findings add to a growing understanding of urban agroecosystem function and support the enemies hypothesis in urban agroecosystems.

Application of UAV remote sensing and machine learning to model and map land use in urban gardens

Urban gardens are an integral part of urban agricultural systems, contributing to ecosystem services, biodiversity and human wellbeing. These systems occur at fine scales, can be highly complex and therefore offer the opportunity to test mechanisms of ecological patterns and processes. The capacity to confidently characterize urban gardens and their land uses is still lacking, while it could provide the basis for assessing ecosystem service provision. Land classifications from remote sensing platforms are common at the landscape scale, but imagery often lacks the resolution required to map differences in land use of fine-scale systems such as urban gardens. Here, we present a workflow to model and map land use in urban gardens using imagery from an unoccupied aerial vehicle (UAV) and machine learning. Due to high resolutions (<5 cm) from image acquisition at low altitudes, UAV remote sensing is better suited to characterize urban land use. We mapped six common land uses in 10 urban community gardens, exhibiting distinct spatial arrangements. Our models had good predictive performance, reaching 80% overall prediction accuracy in independent validation and up to 95% when assessing model performance per cover class. Extracting spatial metrics from these land use classifications, we found that at the garden and plot scale, plant species richness can be estimated by the total area and patchiness of crops. Land use classifications like these can offer an accessible tool to assess complex urban habitats and justify the importance of urban agriculture as a service-providing system, contributing to the sustainability and livability of cities.

On-Farm Spatial Composition, Management Practices and Estimated Productivity of Urban Farms in the San Francisco Bay Area

Urban areas are the fastest growing land type worldwide. By 2060, it is expected that approximately 70% of the human population will live in cities. With increased urban population growth, food sovereignty and security issues have gained more attention, resulting in a drastic increase in urban food production activities including, urban farming and gardening. The extent to which urban farms function, their social, ecological and economic composition, and their overall impact on local food security has become an often overlooked, but important topic. From 2014 to 2017, we partnered with 29 urban farms in the San Francisco Bay Area for a broad-scale survey of urban farm characteristics. Findings reported in this research focused on local (on-farm) characteristics, including management practices, on-farm spatial composition, and estimated productivity. We implemented open-ended surveys for farm managers to better understand management practices, measured on-farm elements, including yields, crop biodiversity, weed composition and abundance, and measured spatial characteristics such as area of production, non-crop area, and proportion of infrastructure to better understand how urban farms were spatially configured. We found trends regarding spatial composition, including a large proportion of farm area dedicated to infrastructure and underutilized potential production space. All farms surveyed had adopted a breadth of agroecological management practices, including cover cropping, crop rotations, intercropping, and a range of soil conservation practices. Measured farms are incredibly productive, with estimated seasonal yields of 7.14 kg/square meter. Estimated yields were comparable with actual yields as measured at two participating farms.

Plant Diversity Increased Arthropod Diversity and Crop Yield in Traditional Agroforestry Systems but Has No Effect on Herbivory

Improving agricultural production in response to the increasing food demand remains a major challenge in agroecology. The world has made significant efforts to meet this issue by developing several cultivation techniques, such as the use of chemical fertilizers and arable land conversion into agricultural land. However, most of these techniques have caused a significant loss of biodiversity and ecosystems services. Recent data suggest that biological conservation within and around agroforestry systems are potential solutions that can both reduce biodiversity loss and guarantee crop production. This logic is based on the hypothesis that increasing plant diversity in and around agricultural systems can limit the pest attack rate and increase crop yield. We tested this hypothesis using structural equation modeling on empirical data collected in agroforestry systems around the Pendjari biosphere reserve in West Africa. We measured crop diversity, crop yield, arthropod pest diversity, abundance, the rate of crop herbivory, and the diversity of plants in surrounding natural vegetation in 32 permanent plots. We estimated arthropod diversity and abundance using pitfall traps. We found a direct positive effect for plant diversity and a direct negative effect of arthropod herbivory on crop yield. The diversity of plants in surrounding natural vegetation had a direct positive effect on arthropod pest diversity but a marginal negative direct effect on the rate of crop herbivory. We found no significant direct or indirect effect for crop diversity. Our findings underline the important role of biodiversity conservation in agricultural production improvement. We suggest that the conservation of plant diversity around agroforestry systems may be an effective option to control herbivory damage. Its combination with other pest control techniques may further limit crop depredation and ensure the long-term conservation of wildlife.