Laboratory and field experiments were conducted to evaluate the potential role of 2 species of wild crucifers (Nasturtium heterophylium and Cardamine hirsuta) in the preservation of Diadegma eucerophaga, an introduced parasitoid of Plutelia xylostelia. In the laboratory, the ichneumonid developed well on P. xylostella larvae reared on leaves of N. heterophyllum and C. hirsuta, suggesting that both may serve as food and oviposition sites for the yponomeutid. In the field, N. heterophyllum and C. hirsuta provided refuge for the ichneumonid when planted adjacent to insecticide-treated cabbage plots. none