Agroecological Pest Management in the City: Experiences from California and Chiapas

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.

Biological Control Services from Parasitic Hymenoptera in Urban Agriculture

“…Confirming these findings are an abundance of patch-matrix literature suggesting that the quality of the habitat patch itself, its size, and the composition of the matrix surrounding it are determining factors for species occurrence in fragmented landscapes [ 20 , 25 , 29 , 30 ]. Specific to UA, higher imperviousness surrounding urban farms has been related to decreased parasitoid abundance and richness [ 31 , 32 ], decreased predator abundance and richness [ 33 , 34 , 35 ], and even decreased predation on sentinel prey [ 36 ].…”

“…Abundance of perennials, height of herbaceous cover, and amount of seminatural or noncrop area on urban farms have been measured in UA and have been shown to positively impact a wide diversity of natural enemies [ 18 ]. Area of ground cover, especially mulch cover, has been correlated with increased natural enemy abundance [ 31 , 32 , 37 ] and richness [ 31 , 39 ]. Increased proportions of complex ground covers have been associated with increased rates of prey removal in sentinel prey trials in urban gardens [ 36 ].…”

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

“…The selected articles were published between 2006–2018; most studies were from Europe or the Northern Hemisphere, with only one of the studies occurring in the Southern Hemisphere [31]. Studies varied by level of taxonomic classification, with most identifying arthropod taxa to morphospecies or family/superfamily.…”

Social Context Influence on Urban Gardener Perceptions of Pests and Management Practices

“…Agroecological principles, where external inputs are replaced by natural processes, have been applied to improve small scale agriculture for years (Altieri, 1995) and the same principles can be applied to urban gardens and farms (Gregory et al, 2016;Altieri and Nicholls, 2018). In particular, agroecological practices for preventing pests (i.e., avoiding that herbivore populations reach damage thresholds in the first place), can be implemented in urban agroecosystems by managing farms or gardens and surrounding landscapes to conserve biological control agents and minimize herbivore damage (Morales et al, 2018). There is a growing number of studies in urban gardens that investigate the local and landscape factors that affect insect predators and parasitoids (pest control agents or natural enemies) (Gardiner et al, 2014;Egerer et al, 2017Egerer et al, , 2018aPhilpott and Bichier, 2017;Lowenstein and Minor, 2018;Morales et al, 2018), providing valuable information that could be disseminated to urban gardeners (Arnold et al, 2019).…”

“…In particular, agroecological practices for preventing pests (i.e., avoiding that herbivore populations reach damage thresholds in the first place), can be implemented in urban agroecosystems by managing farms or gardens and surrounding landscapes to conserve biological control agents and minimize herbivore damage (Morales et al, 2018). There is a growing number of studies in urban gardens that investigate the local and landscape factors that affect insect predators and parasitoids (pest control agents or natural enemies) (Gardiner et al, 2014;Egerer et al, 2017Egerer et al, , 2018aPhilpott and Bichier, 2017;Lowenstein and Minor, 2018;Morales et al, 2018), providing valuable information that could be disseminated to urban gardeners (Arnold et al, 2019). Because of its high levels of socio-economic and ecological complexity, where top-down approaches have been shown to have little to no impact (Van Veenhuizen et al, 2001;Prain, 2006), the promotion of agroecological methods for pest control in UA should incorporate participatory methods (Morales and Perfecto, 2000).…”