Insects in the City: Evaluating Pollination and Biological Control in Urban Neighborhoods

Cities are a dynamically shifting entity with environmental disturbances and social and economic forces that affect plants and arthropods. Although a decline in habitat quality generally reduces arthropod biodiversity along a rural-urban gradient, researchers have only recently examined community-level patterns within urban boundaries. In this dissertation, I examined plant-pollinator interactions and prey suppression from natural enemies in residential neighborhoods and urban agriculture. Pollinators and natural enemies are desirable for crop productivity and the potential to reduce insecticide application against herbivores. In chapter 1, I investigated pollination services in an array of potted garden plants. This study found that several efficient pollinators remain in cities. While these pollinators partitioned visits uniquely among different plant species, yield was similar in each species. In chapter 2, I evaluated patterns of floral community and attributes in neighborhoods. The greatest floral species richness occurred in ethnically diverse neighborhoods and areas with intermediate development intensity. Most plant species in Chicago, IL are non-native and perennial, but I identified that most pollinator visits were restricted to a sub-group of plants belonging to weedy and perennial species (Chapter 3). These modified visitation patterns influenced network characteristics. In the final two chapters of this dissertation I focused on predatory-prey interactions in brassica, a commonly cultivated plant family in urban agriculture. I investigated if the resource concentration hypothesis applies in the urban setting by comparing cabbageworm and aphid pests in three scales of food production. Additionally, I analyzed the influence of top-down herbivore control by natural enemies. I identified a diverse natural community in each agricultural scale, which was a stronger force at regulating herbivores (Chapter 4). Prey suppression was similar in each scale and across the urban landscape (Chapter 5). Most sentinel cabbage looper items were attacked by predators. By researching patterns in urban biodiversity within cities, I identified how fine scale variation in landscape and local factors mediate plant, pollinator, and natural enemies in densely populated areas. This information can be used to identify areas for extra resources and conservation priority.