Evaluating Biological Control of Brassica Pests in Urban Land Repurposed for Farming

Student Investigator: David Lowenstein, Department of Biological Science, University of Illinois-Chicago, [email protected]

Faculty Advisor: Emily Minor, Department of Biological Science, University of Illinois-Chicago, [email protected]

Project period: 2014-2016


Urban farms bring economic and ecological productivity to underdeveloped spaces in Midwestern (USA) cities. As planted row and vegetable crops are added, there is increased susceptibility to plant damage by herbivorous pests. We surveyed urban farm managers on perceived risks of crop damage from insect pests. Based on the survey results, we investigated the effects of surrounding landscape and production type on natural enemy and pest populations. We investigated natural enemy and pest populations in urban agriculture and the potential of insect predators and parasitoids to control cabbageworms and aphids in community gardens and urban farms. In a laboratory assay, we measured the efficacy of natural enemies at suppressing cabbage looper. In another experiment, we investigated the impact of supplemental floral resources on natural enemies and brassica production. Urban agriculture contains a diverse community of natural enemies, dominated by parasitoid wasps and several predator groups. Cabbageworms and aphids were present at low, but similar, densities at community and urban farms. Brassica defoliation was less than 20%, on average, across sites. The lab study identified lady beetles as the most effective predator of cabbageworm eggs. In gardens, we found greater mortality in cabbage loooper eggs compared to larvae. Natural enemy abundance did not affect mortality rates, and variation in cabbage looper mortality was poorly explained by within-garden or landscape factors. The diverse natural enemy community in urban farms provides a positive outlook for growers relying on biological control as a tool in pest management. Our results confirm the roles of generalist predators in suppressing pest populations in urban agriculture.