Evaluating parasitoids and biocontrol of brassica pests in urban food production sites

Blighted and underutilized spaces are increasingly being converted to agricultural use in Midwestern (USA) cities. Urban agriculture provides an economic benefit to local communities and can support arthropod communities. However, recently planted vegetable crops will also be susceptible to insect damage as pests locate new forage. We investigated natural enemies, including parasitoids, in brassica plants by placing yellow sticky cards at 29 food production sites in Chicago, IL. Cards were replaced bi-weekly for a 10 week period, and we counted aphids and caterpillar pests on brassica, when replacing sticky cards. Using cabbage looper larvae and egg masses (Trichoplusia ni) as sentinel prey items, we compared the rate of biological control between private residential gardens, community gardens, and urban farms. Larger urban farms had significantly greater populations of cabbage worm eggs and larvae and aphids than smaller residential gardens. Cabbage looper egg masses experienced 50% mortality, on average and were attacked by several predators and parasitoids. However, we did not record a significant association between parasitoid abundance and biocontrol rate. Although there was not a direct connection between natural enemies trapped on yellow cards and the rate of biocontrol, we speculate that surrounding habitat or garden management practices may affect the potential for biocontrol. We provided evidence that urban food production sites experience variable levels of pest pressure and suggest that natural enemies be further evaluated for their success at biocontrol in a highly disturbed environment.