Germ line transformation is a powerful research tool to probe and manipulate gene function but currently the number of insect species transformed is small and biased towards Diptera. Here we develop transgenic techniques for a butterfly in the family Pieridae, the widely-studied cabbage white butterfly (Pieris rapae L; Lepidoptera: Pieridae). Germ line transformation of pierids is useful because butterfly wing patterns have become model systems in evolutionary developmental biology, and the previously transformed butterflies are members of a different family, the nymphalids. We used a piggyBac[3xP3-EGFP] construct as a marker for germ line transformation and obtained a single transformed adult that did not reproduce but which displayed fluorescence in its eyes. After identifying the genomic insertion site for the construct we conclude that this individual was likely transgenic. However, short of longer-term inheritance data, we discuss two less likely alternative possibilities for our data.