Pieris rapae L., an invasive crop pest, may have recently begun using Alliaria petiolata Bieb. (Cavara & Grande), a European invasive biennial. We investigated how P. rapae uses forest habitats for nectar and oviposition and examined larval performance on A. petiolata in the field and laboratory. Being known primarily to occupy open habitats, we found that P. rapae regularly uses forest edge habitats, most surveyed A. petiolata plants had P. rapae damage, and P. rapae successfully used both stages of A. petiolata for larval development.